Hans-Joachim Wunderlich (i.R.)

Abstract

Small Delay Faults (SDFs) due to weak defects and marginalities have to be distinguished from extra delays due to process variations, since they may form a reliability threat even if the resulting timing is within the specification. In this paper, it is shown that these faults can still be identified, even if the corresponding defect cell is deeply embedded into a combinational circuit and its observability is restricted. The results of a few delay tests at different voltages and frequencies serve as the input to machine learning procedures which can classify a circuit as marginal due to defects or just slow due to variations. Several machine learning techniques are investigated and compared with respect to accuracy, precision, and recall for different circuit sizes and defect scales. The classification strategies are powerful enough to sort out defective devices without a major impact on yield.

Abstract

Reconfigurable Scan Networks (RSNs) are widely used for accessing instruments offline during debug, test and validation, as well as for performing sys-tem-level-test and online system health monitoring. The correct operation of RSNs is essential, and RSNs have to be thoroughly tested. However, due to their inherently sequential structure and complex control dependencies, large parts of RSNs have limited observability and controllability. As a result, certain faults at the interfaces to the instruments, control primitives and scan segments remain undetected by existing test methods. In the paper at hand, Design-for-test (DfT) schemes are developed to overcome the testability problems e.g. by resynthesizing the initial design. A DfT scheme for RSNs is presented, which allows detecting all single stuck-at-faults in RSNs by using existing test generation techniques. The developed scheme analyzes and ensures the testability of all parts of RSNs, which include scan segments, control primitives, and interfaces to the instruments. Therefore, the developed scheme is referred to as a complete DfT scheme. It allows for a test integration to cover multiple fault locations can with a single efficient test sequence and to reduce overall test cost.

Abstract

Innovative manufacturing processes allow the integration of billions of transistors into a single chip, and the implementation of extremely dense designs, but they also come with increased variability and new reliability threats. Both, new processes and more complex designs introduce a higher degree of indeterminism which challenges logic diagnosis and defect classification. Design techniques like selective hardening, fault masking, and error masking or adaptive voltage and frequency scaling (AVFS) increase reliability, but make test, diagnosis, and defect classification even more difficult. This chapter presents machine learning techniques for distinguishing variations from reliability threats due to defects, for identifying different defect types during diagnosis, and for distinguishing transient errors covered by hardening or masking from intermittent faults.

Abstract

Adaptive Voltage Frequency Scaling (AVFS) is an important means to overcome process-induced variability challenges for advanced high-performance circuits. AVFS requires and allows determining the maximum speed Fmax(Vdd) reachable under a set of certain operation voltages Vdd. In this paper, it is shown that the Fmax(Vdd) measurements contain relevant data to identify some hidden defects in a chip which are reliability threats and can cause device failures, but pass the speed binning procedure within the given specifications. Static Timing Analysis (STA) is applied to a circuit designed by using standard cell libraries in which the underlying transistors along with process variations have been carefully calibrated against industrial 14nm FinFET measurement data, and instances with and without injected small resistive open defects are generated. From the slope of the function Fmax(Vdd), a machine learning procedure can identify some defects with high accuracy and few false positives. These chips can be then discarded without any further need and cost for testing. It has to be noted that this reliability information comes for free from the data which is already generated, and does not need any additional measurements.

Abstract

Reconfigurable Scan Networks (RSNs) access embedded instruments throughout the whole system lifecycle. To support dependability management by means of RSNs, RSNs themselves must be continuously tested. The paper-at-hand presents the first online periodic test method for RSNs. The developed algorithm generates a short sequence of test patterns, which tests all parts of an RSN. The generated sequence is uploaded on-chip and is applied periodically to avoid fault accumulation in RSNs. The overall test application time is minimized to comply with the timing requirements of the well-known safety standards. The experimental results show that the method is efficient for all considered RSN designs and is scalable with the increasing size and complexity of RSNs.

Abstract

Both process variations and defects in cells can lead to additional small delays within specifications, while the latter must be identified because they may degrade soon into critical faults for circuits and result in threat to reliability. Therefore, discriminating small delays due to defects from those due to variations has drawn increasingly attention in the test community over the recent years. One promising research direction is to formulate the task into binary classification by using delays under a few supply voltages as the only variables for datadriven algorithms. However, many approaches often assume the availability of delay information from both defective and nondefective cells or combinational circuits. This assumption implies a large time consumption for simulation, and considerable costs for manufactured defective devices. To address the issues above, this paper proposes to use unsupervised deep learning technique to train an recognizer on non-defective data only but still can identify defects during inference. Specifically, we have proposed weighted autoencoder with a novel data augmentation technique to solve this problem. Experiments show that our approach has comparable detection capability as supervised learning schemes, while our method does not require any defective data. Moreover, our approach is more robust to unbalanced datasets and to nontarget defects than other methods.

Abstract

Reconfigurable Scan Networks (RSNs) access the evaluation results from embedded instruments and control their operation throughout the device lifetime. At the same time, a single fault in an RSN may dramatically reduce the accessibility of the instruments. During post-silicon validation, it may prevent extracting the complete data from a device. During online operation, the inaccessibility of runtime-critical instruments via a defect RSN may eventually result in a system failure. This paper addresses both scenarios above by presenting robust RSNs. We show that by making a small number of carefully selected spots in RSNs more robust, the entire access mechanism becomes significantly more reliable. A flexible cost function assesses the importance of specific control primitives for the overall accessibility of the instruments. Following the cost function, a minimized number of spots is hardened against permanent faults. All the critical instruments as well as most of the remaining instruments remain accessible through the resulting RSNs even in the presence of defects. In contrast to state-of-the-art fault-tolerant RSNs, the presented approach does not change the RSN topology and needs less hardware overhead. Selective hardening is formulated as a multi-objective optimization problem and solved by using an evolutionary algorithm. The experimental results validate the efficiency and the scalability of the approach.

Abstract

Reconfigurable Scan Networks (RSNs) enable an efficient reliability management throughout the device lifetime. They can be used for controlling integrated instruments, such as aging monitors or built-in self-test (BIST) registers, as well as for collecting the evaluation results from them. At the same time, they may impose a security threat, since the additional connectivities introduced by the RSN can possibly be misused as a side-channel. This paper presents an approach for Security Compliance Analysis and Resynthesis (SCAR) of RSNs to integrate an RSN compliant with the security properties of the initial design. First, the reachability properties of the original design are accurately computed. The connectivities inside the RSN, which exceed the allowed connectivity of the initial design, are identified using the presented Security Compliance Analysis. Next, all violations are resolved by automated Resynthesis with a minimized number of structural changes. As a result of SCAR, any information leakage due to the RSN integration is prevented, while the accessibility of the instruments through the RSN is preserved. The approach is able to analyze complex control dependencies and obtains a compliant RSN even for the largest available benchmarks.

Abstract

Safety-critical systems have to follow extremely high dependability requirements as specified in the standards for automotive, air, and space applications. The required high fault coverage at runtime is usually obtained by a combination of concurrent error detection or correction and periodic tests within rather short time intervals. The concurrent scheme ensures the integrity of computed results while the periodic test has to identify potential aging problems and to prevent any fault accumulation which may invalidate the concurrent error detection mechanism. Such periodic built-in self-test (BIST) schemes are already commercialized for memories and for ran- dom logic. The paper at hand extends this approach to inter- connect structures. A BIST scheme is presented which targets interconnect defects before they will actually affect the system functionality at nominal speed. A BIST schedule is developed which significantly reduces aging caused by electromigration during the lifetime application of the periodic test.

Abstract

Runtime/reconfigurable architectures based on Field-Programmable Gate Arrays (FPGAs) are a promising augment to conventional processor architectures such as Central Processing Units (CPUs) and Graphic Processing Units (GPUs). Since the reconfigurable parts are typically manufactured in the latest technology, they may suffer from aging and environmentally induced dependability threats. In this chapter, strategic online test methods for dependable runtime-reconfigurable architectures as well as cross-layer optimizations for high reliability and lifetime are developed. Firstly, two orthogonal online tests are proposed that ensure reliable configuration of the reconfigurable fabric and aid fault detection. Secondly, a novel design method called module diversification is presented that enables self-repair of the system in case of faults caused by degradation effects as well as single-event upsets in the configuration. Thirdly, a novel stress-aware placement method is proposed that aims for slowing down system degradation by aging effects. The combined methods ensure reliable operation across architectural and gate level and allow to prolong the lifetime of dependable runtime-reconfigurable architectures.

Abstract

Small Delay Faults (SDFs) due to defects and marginalities have to be distinguished from extra delays due to process variations, since they may form a reliability threat even if the resulting timing is in the specification. In this paper, it is shown that these faults can still be identified, even if the corresponding defect cell is deeply embedded into a combinational circuit and its behavioral features are affected by several masking impacts of the rest of the circuit. The results of a few delay tests at different voltages and frequencies serve as the input to machine learning procedures which can classify a circuit as marginal due to defects or just slow due to variations. Several machine learning techniques are investigated and compared with respect to accuracy, precision, and recall for different circuit sizes and defect scales. The classification strategies are powerful enough to sort out defect devices without a major impact on yield.

Abstract

The reliable operation of integrated systems issupported by Reconfigurable Scan Networks (RSNs) which allow to access efficiently the embedded instruments throughout the life-cycle. However, the RSN integration may introduce additional connectivities into a Device-under-Test (DUT), and the RSN might be misused for information leakage. Structural methods resynthesize the RSNs and add hardware components such that certain instruments are physically separated, while functional approaches add filters to prevent certain access patterns. Both methods have certain limitations. This paper presents an effective approach to maximize the benefits and to overcome the limitations of the existing solutions by a hybrid combination of structural and functional protection schemes. A minimized number of structural changes is identified in order to resolve violations which cannot be handled by using sequence filters. The remaining violations are resolved functionally by using filters and a flexible protection can be enabled for multiple user groups with different access permissions. Since the majority of the violations are resolved using a filter, the hardware overhead for structural changes is drastically reduced. The efficiency of the approach is supported by experimental results.

Abstract

Reconfigurable Scan Networks (RSNs) have to be tested before they can be used for post-silicon validation, diagnosis or online reliability management. Even a single stuck-at fault in the switch logic of an RSN can corrupt the scan paths and make instruments inaccessible. Testing the switch logic of an RSN is a complex sequential test problem. The existing test schemes for RSNs rely on the assumption that a fault in the switch logic will be detected by the altered length of the erroneously activated scan path. However, often this assumption does not hold and faults in the switch logic remain undetected. In this paper, an automated testability-enhancing resynthesis is presented. First, the testability of the initial RSN is accurately analyzed. If any single fault in the switch logic is undetectable by the altered path length, a small number of scan cells is inserted into the RSN. The presented scheme is applicable to arbitrary RSN designs and is compliant with state-of-the-art test methods and the applicable standards. The experimental results show the efficacy, the efficiency and the scalability of the approach.

Abstract

Self-aware and safety-critical hardware/software systems rely on a variety of embedded instruments, sensors, monitors and design-for-test circuitry to check the system integrity. The access to these internal instruments is supported by standards commonly called iJTAG and employs so called reconfigurable scan networks (RSNs), which are more and more used at runtime, too. They collect periodically and also concurrently the information on the circuit’s health state and deliver it to some dependability management unit. The integrity of RSNs is essential for the dependability of selfaware systems and can be ensured by a combination of periodic and concurrent test methods of the RSN itself. The paper at hand presents the first concurrent online test method for RSNs by adding a brief integrity test to each access operation. The presented scheme includes a hardware extension of negligible size, supports offline test, diagnosis and post-silicon validation as well, and is further referred as ROSTI : RSN Online/Offline SelfTest Infrastructure. It exploits the original RSN control signals and does not require any modification of the underlying RSN. The hardware costs are independent of the size of the RSN, and ROSTI is flexible for generating different test sequences for different types of faults. The experimental results validate these characteristics and show that ROSTI is highly scalable.

Abstract

Reliable operation, test, debug and diagnosis of complex integrated systems are ensured by em-bedded instruments, such as sensors, aging monitors or Built-In Self-test (BIST) registers. Reconfigurable Scan Networks (RSNs) offer a flexible and efficient way to access such test instruments throughout the whole life-cycle. However, improper RSN integration might introduce additional connectivity properties to the device under test (DUT), which can be exploited to perform unauthorized access or cause information leakage. The existence of such additional connectivity through the RSN can compromise the security of the DUT and is considered as a security threat.In this paper, a method is presented to resolve all such security compliance violations. The problem is formulated in terms of Integer Linear Programming (ILP) as a minimum cut problem in multicommodity flow. An efficient heuristic is presented, which, to our knowledge, for the first time allows to consider the whole set of violations simultaneously and thereby to find a minimized number of changes to the RSN structure in order to make it compliant with the initial security requirements of the DUT and prevent the information leakage through the scan chain.

Abstract

Timing validation of systems with adaptive voltage-and frequency scaling (AVFS) requires an accurate timing model under multiple operating points. Simulating such a model at gate level is extremely time-consuming, and the state-of-the-art compromises both accuracy and compute efficiency.This paper presents a method for dynamic gate delay modeling on graphics processing unit (GPU) accelerators which is based on polynomial approximation with offline statistical learning using regression analysis. It provides glitch-accurate switching activity information for gates and designs under varying supply voltages with negligible memory and performance impact. Parallelism from the evaluation of operating conditions, gates and stimuli is exploited simultaneously to utilize the high arithmetic computing throughput of GPUs. This way, large-scale design space exploration of AVFS-based systems is enabled. Experimental results demonstrate the efficiency and accuracy of the presented approach showing speedups of three orders of magnitude over conventional time simulation that supports static delays only.

Abstract

Hidden delay defects (HDDs) are small delay defects that pass all at-speed tests at nominal capture time. They are an important indicator of latent defects that lead to early-life failures and aging problems that are serious especially in autonomous and medical applications. An effective way to screen out HDDs is to use Faster-than-At-Speed Testing (FAST) to observe outputs of sensitized non-critical paths which are expected to be stable earlier than nominal capture time.To improve the reliability of current and future designs, it is important to learn about the population of HDDs using logic diagnosis. We present the very first logic fault diagnosis technique that is able to identify HDDs by analyzing fail logs produced by FAST. Even with aggressive FAST testing, HDDs generate only very few failing test response bits. To overcome this severe challenge, we propose new backtracing and response matching methods that yield high diagnostic success rates even with very limited amount of failure data. The performance and scalability of our HDD diagnosis method is validated using fault injection campaigns with large benchmark circuits.

Abstract

Small Delay Faults (SDFs) are an indicator of reliability threats even if they do not affect the behavior of a system at nominal speed. Various defects may evolve over time into a complete system failure, and defects have to be distinguished from delays due to process variations which also change the circuit timing but are benign. Based on Monte-Carlo ectrical simulation at cell level, in this work it is shown that a few measurements at different operating points of voltage and frequency are sufficient to identify a defect cell even if its behavior is completely within the specification range. The developed classifier is based on statistical learning and can be annotated to each element of a cell library to support manufacturing test, diagnosis and optimizing the burn-in process or yield.

Abstract

Early life failures in marginal devices are a severe reliability threat in current nano-scaled CMOS devices. While small delay faults are an effective indicator of marginalities, their detection requires special efforts in testing by so-called Faster-than-At-Speed Test (FAST). In a similar way, delay degradation is an indicator that a device reaches the wear-out phase due to aging. Programmable delay monitors provide the possibility to detect gradual performance changes in a system and allow to observe device degradation.This paper presents a unified approach to test small delay faults related to wear-out and early-life failures by reuse of existing programmable delay monitors within FAST. The approach is complemented by a test-scheduling which optimally selects frequencies and delay configurations to significantly increase the fault coverage of small delays and to reduce the test time.

Abstract

Systems with adaptive voltage-and frequency scaling (AVFS) require timing validation with accurate timing models under multiple operating points. Since, these models are typically simulated at logic level and extremely time-consuming, the state-of-the-art often compromises both accuracy and speed. This paper presents the first massively parallel switch level time simulator with parametric delay modeling for efficient timing-accurate validation of systems with AVFS. It provides full glitch-accurate switching activity information of designs under varying supply voltage and temperature. Offline statistical learning with regression analysis is employed to generate polynomials for dynamic delay modeling by approximation of the first-order electrical parameters of CMOS standard cells. With the parallelization on graphics processing units and simultaneous exploitation of multiple dimensions of parallelism the simulation throughput is maximized and scalable-design space exploration of AVFS-based systems is enabled. Results demonstrate the efficiency and accuracy with speedups of up to 159x over conventional logic level time simulation with static delays.

Abstract

On-chip instrumentation is mandatory for efficient bring-up, test and diagnosis, post-silicon validation, as well as in-field calibration, maintenance, and fault tolerance. Reconfigurable scan networks (RSNs) provide a scalable and efficient scan-based access mechanism to such instruments. The correct operation of this access mechanism is crucial for all manufacturing, bring-up and debug tasks as well as for in-field operation, but it can be affected by faults and design errors. This work develops for the first time fault-tolerant RSNs such that the resulting scan network still provides access to as many instruments as possible in presence of a fault. The work contributes a model and an algorithm to compute scan paths in faulty RSNs, a metric to quantify its fault tolerance and a synthesis algorithm that is based on graph connectivity and selective hardening of control logic in the scan network. Experimental results demonstrate that fault-tolerant RSNs can be synthesized with only moderate hardware overhead.

Abstract

Marginal hardware introduces severe reliability threats throughout the life cycle of a system. Although marginalities may not affect the functionality of a circuit immediately after manufacturing, they can degrade into hard failures and must be screened out during manufacturing test to prevent early life failures. Furthermore, their evolution in the field must be proactively monitored by periodic tests before actual failures occur. In recent years small delay faults have gained increasing attention as possible indicators of marginal hardware. However, small delay faults on short paths may be undetectable even with advanced timing aware ATPG. Faster- than-at-speed test (FAST) can detect such hidden delay faults, but so far FAST has mainly been restricted to manufacturing test. This paper presents a fully autonomous built-in self-test (BIST) approach for FAST, which supports in-field testing by appropriate strategies for test generation and response compac- tion. In particular, the required test frequencies for hidden delay fault detection are selected, such that hardware overhead and test time are minimized. Furthermore, test response compaction handles the large number of unknowns (X-values) on long paths by storing intermediate MISR-signatures in a small on-chip memory for later analysis using X-canceling transformations. A comprehensive experimental study demonstrates the effectiveness of the presented approach. In particular, the impact of the considered fault size is studied in detail.

Abstract

The chapter discusses the background for the most demanding dependability hallenges for reconfigurable processors in many-core systems and presents a dependable runtime reconfigurable processor for high reliability. It uses an adaptive modular redundancy technique that guarantees an application-specified level of reliability under changing SEU rates by budgeting the effective critical bits among all kernels and all accelerators of an application. This allows to deploy reconfigurable processors in harsh environments without statically protecting them.

Abstract

Reconfigurable Scan Networks (RSNs) allow flexible access to embedded instruments for post-silicon test, validation and debug or diagnosis. The increased observability and controllability of registers inside the circuit can be exploited by an attacker to leak or corrupt critical information. Precluding such security threats is of high importance but difficult due to complex data flow dependencies inside the reconfigurable scan network as well as across the underlying circuit logic. This work proposes a method that fine-granularly computes dependencies over circuit logic and the RSN. These dependencies are utilized to detect security violations for a given insecure RSN, which is then transformed into a secure RSN. Experimental results demonstrate the applicability of the method to large academical and industrial designs. Additionally, we report on the required effort to mitigate found security violations which also motivates the necessity to consider the circuit logic in addition to pure scan paths.

Abstract

Hardware security adds another dimension to the design space, and more and more attention is paid to protect a circuit against various types of attacks like sniffing, spoofing or IP theft. However, all the efforts for security taken by a designer might be sacrificed by afterwards integrating infrastructure for test, diagnosis and reliability management. Especially, access mechanisms like reconfigurable scan networks (RSNs) may open options for side-channel attacks. In this paper, an exact method is presented to verify that a specified RSN does not introduce a new data path which was not already present in the original design. The method uses a matrix-based reachability analysis of the original design and the augmented design.The reachability analysis covers complex functional dependencies, caused by configuring a single scan path as well as multiple sequentially activated scan paths through the RSN. %An accurate computation of the set of functionally possible paths introduced by integrating an RSN into the design is done and used to determine whether any new data paths have been added to the design. This approach adds acceptable runtime to the security verification flow of the design, and shows the designer the introduced possible security violations.

Abstract

In CMOS technology first-order parametric faults during manufacturing can exhibit severe changes in the timing as well as in the functional behavior of cells. Since these faults are hard to detect by conventional tests, the accurate simulation of these low-level faults plays an important role for test validation. However, pure low-level fault simulation approaches impose a high computational complexity that can quickly become inapplicable to larger simulation problems due to limitations in scalability. In this paper, the first parallel multi-level fault simulation approach on graphics processing units (GPUs) is presented. The approach utilizes both logic level and switch level descriptions concurrently in a mixed-abstraction timing simulation. The abstraction is lowered in user-defined so-called regions of interest that locally increase the modeling accuracy enabling low-level first-order parametric fault injection. Resulting signal waveforms are transformed between the different abstractions transparently. This way a fast, versatile and efficient multi-level fault simulation approach on GPUs is created that scales for designs with millions of cells while achieving high simulation throughput with runtime savings of up to 84% compared to full switch level simulations.

Abstract

Current nanometer CMOS circuits show an increasing sensitivity to deviations in first-order parameters and suffer from process variations during manufacturing. To properly assess and support test validation of digital designs, low-level fault simulation approaches are utilized to accurately capture the behavior of CMOS cells under parametric faults and process variations as early as possible throughout the design phase. However, low-level simulation approaches exhibit a high computational complexity, especially when variation has to be taken into account. In this work a high-throughput parallel fault simulation at switch level is presented. First-order electrical parameters are utilized to capture CMOS-specific functional and timing behavior of complex cells allowing to model faults with transistor granularity and without the need of logic abstraction. Furthermore, variation modeling in cells and transistor devices enables broad and efficient variation analyses of faults over many circuit instances for the first time. The simulation approach utilizes massive parallelization on Graphics Processing Units (GPUs) by exploiting parallelism from cells, stimuli, faults and circuit instances. Despite the lower abstraction levels of the approach, it processes designs with millions of gates and outperforms conventional fault simulation at logic level in terms of speed and accuracy.

Abstract

With today’s tight timing margins, increasing manufacturing variations, and new defect behaviors in FinFETs, effective yield learning requires detailed information on the population of small delay defects in fabricated chips. Small delay fault diagnosis for yield learning faces two principal challenges: (1) production test responses are usually highly compacted reducing the amount of available failure data, and (2) failure signatures not only depend on the actual defect but also on omnipresent and unknown delay variations. This work presents the very first diagnosis algorithm specifically designed to diagnose timing issues on compacted failure data and under process variations. An innovative combination of variation-invariant structural anal- ysis, GPU-accelerated time-simulation, and variation-tolerant syndrome matching for compacted test responses allows the proposed algorithm to cope with both challenges. Experiments on large benchmark circuits clearly demonstrate the scalability and superior accuracy of the new diagnosis approach.

Abstract

Modern systems-on-chip (SoC) designs are requiring more and more infrastructure for validation, debug, volume test as well as in-field maintenance and repair. Reconfigurable scan networks (RSNs), as allowed by IEEE 1687 (IJTAG) standard, provide flexible access to the infrastructure with low access latency. However, they can also pose a security threat to the system, by leaking information about the system state. In this paper, we present a protection method that monitors access and checks for violations of security properties online. The method prevents unauthorized access to sensitive and secure instruments. In addition, the system integrator can specify more complex security requirements, including giving multiple users different access privileges. Simultaneous accesses to multiple instruments, that would expose sensitive data to an untrusted core (e.g. from 3rd party vendors) or instrument, can be prohibited. The method does not require any change to the RSN architecture and is easily integrable with IP core designs. The area overhead with respect to the size of the RSN is below 6% and scales well with larger networks.

Abstract

Self-awareness allows autonomous systems the dynamic adaptation to changing states of the hardware platform and the optimal usage of available computing resources. This demands concurrent, periodical, or on-demand monitoring and testing of the hardware structures to detect and classify deviations from the nominal behavior and appropriate reactions. This survey discusses suitable self-test, self-checking, and self-diagnosis methods for the realization of self-awareness and presents two case studies in which such methods are applied at different levels.

Abstract

Approximate computing exploits the inherent error resilience of many applications to optimize power consumption, run time, or chip area. Especially in audio, image, and video processing, but also in data mining or resource allocation tasks, approximate results are "good enough" for many application domains and may be hard to distinguish from perfect results. But even in domains where accurate results are required, approximate computing can be applied in various layers of the computing stack. Approximate computing promises to significantly increase computing efficiency (especially performance per power) and power density and is therefore of particular interest for embedded computing where these metrics are key.

Abstract

Timing-accurate simulation of circuits is an important task in design validation of modern nano-scale CMOS circuits. With shrinking technology nodes, detailed simulation models down to transistor level have to be considered. While conventional simulation at logic level lacks the ability to accurately model timing behavior for complex cells, more accurate simulation at lower abstraction levels becomes computationally expensive for larger designs. This work presents the first parallel multi-level waveform-accurate timing simulation approach on graphics processing units (GPUs). The simulation uses logic and switch level abstraction concurrently, thus allowing to combine their advantages by trading off speed and accuracy. The abstraction can be lowered in arbitrary regions of interest to locally increase the accuracy. Waveform transformations allow for transparent switching between the abstraction levels. With the utilization of GPUs and thoughtful unification of algorithms and data structures, a fast and versatile high-throughput multi-level simulation is obtained that is scalable for millions of cells while achieving runtime savings of up to 89% compared to full simulation at switch level.

Abstract

Device aging is an important concern in nanoscale designs. Due to aging the electrical behavior of transistors embedded in an integrated circuit deviates from original intended one. This leads to performance degradation in the underlying device, and the ultimate device failure. This effect is exacerbated in emerging technologies. To be able to tailor effective aging mitigation schemes and improve the reliability of devices realized in cutting edge technologies, there is a need to accurately study the effect of aging in high performance industrial applications. According, this paper targets a high performance SRAM memory realized in 14nm FinFET technology and depicts how aging degrades the individual components of this memory as well as the interaction between them. Aging mitigation is critical not only from device reliability point of view but also regarding device security perspectives. It is essential to assure the security of the sensitive tasks performed by the security-sensitive circuits and to guarantee the security of information stored within these devices in the presence of aging. Accordingly in this paper, we also focus on aging-related security concerns and present the cases in which aging need to considered to preserve security.

Abstract

Aging monitors can indicate the wear-out phase of a semi-conductor device before it will actually fail, and allow the use of integrated circuits in applications with high safety and reliability demands. In the early phase of the lifecycle of integrated systems, small delay faults may indicate reliability problems and early life failures, even if they are smaller than the slack of any path and neither alter the functional behavior of a system nor violate any aging guardband. One option to detect this type of hidden delay faults (HDFs) is the application of a faster-than-at-speed-test (FAST). This paper shows that aging monitors can be extended at low cost to achieve high HDF test coverage with a reduction in test time during FAST. The result is a unified strategy to improve the reliability in both early and late phases of the system lifecycle.

Abstract

Reconfigurable Scan Networks (RSNs) allow flexible access to embedded instruments for post-silicon validation and debug or diagnosis. However, this scan infrastructure can also be exploited to leak or corrupt critical information as observation and controllability of registers deep inside the circuit are increased. Securing an RSN is mandatory for maintaining safe and secure circuit operations but difficult due to its complex data flow dependencies. This work proposes a method that detects security violations and transforms a given insecure RSN into a secure RSN for which the secure data flow as specified by a user is guaranteed by construction. The presented method is guided by user-defined cost functions that target e.g. test performance or wiring cost. We provide a case study and experimental results demonstrating the applicability of the method to large designs with low runtime.

Abstract

Automotive microelectronics are gaining great impact with the advent of electromobility and self-driving cars. Being a mass market, cost sensitivity is a major concern, while the functional safety, security, stringent run-time requirements and reliable operation are still major challenges. Automotive Reliability and Test (ART) has been the most popular topic at the recent IEEE International Test Conferences, and the ART Workshop 2016 in conjunction with ITC was extremely popular. This special issue of IEEE Design&Test originates from this workshop and deals with the most significant topics in automotive reliability and test.

Abstract

High scan shift power often leads to excessive heat as well as other severe problems such as shift timing failures. Partial shift (shifting only a subset of scan chains at a time) is a widely-adopted general approach for mitigating shift power problems. Although partial shift is effective in avoiding excessive heat by reducing global switching activity, we show for the first time that it may actually worsen shift clock skews, thus increasing the risk of shift timing failures. This paper addresses this problem with an innovative method, namely Clock-Skew-Aware Scan Chain Grouping (CSA-SCG). CSA-SCG properly groups scan chains to be shifted simultaneously so as to reduce the imbalance of switching activity around the clock paths for neighboring scan flip-flops in the scan chains. Experiments on large ITC'99 benchmark circuits demonstrate the effectiveness of CSA-SCG for reducing scan shift clock skews to lower the risk of shift timing failures in partial shift.

Abstract

Iterative solvers like the Preconditioned Conjugate Gradient (PCG) method are widely-used in compute-intensive domains including science and engineering that often impose tight accuracy demands on computational results. At the same time, the error resilience of such solvers may change in the course of the iterations, which requires careful adaption of the induced approximation errors to reduce the energy demand while avoiding unacceptable results. A novel adaptive method is presented that enables iterative Preconditioned Conjugate Gradient (PCG) solvers on Approximate Computing hardware with high energy efficiency while still providing correct results. The method controls the underlying precision at runtime using a highly efficient fault tolerance technique that monitors the induced error and the quality of intermediate computational results.

Abstract

Design, production and operation of modern system-on-chips rely on integrated instruments, which range from simple sensors to complex debug interfaces and design-for-test (DfT) structures. Reconfigurable scan networks (RSNs) as defined in IEEE Std. 1687-2014 provide an efficient access mechanism to such instruments. It is essential to test the access mechanism itself before it can be used for test, diagnosis, validation, calibration or runtime monitoring. Realistic fault mechanisms in RSNs are hard to test due to their high sequential depth and limited controllability and observability via serial scan ports. We present a novel low-cost DfT modification specifically designed for RSNs that enhances the observability of shadow registers. Furthermore, we present different test methods for stuck-at and more realistic gate-level fault models like flip-flop- internal and bridge faults. Experimental results demonstrate the effectiveness of the presented DfT modification and test methods.

Abstract

In recent years early life failures have caused several product recalls in semiconductor and automotive industries associated with a loss of billions of dollars. They can be traced back to various root-causes. In embedded or cyber-physical systems, the interaction with the environment and the behavior of the hardware/software interface are hard to predict, which may lead to unforeseen failures. In addition to that, defects that have escaped manufacturing test or “weak” devices that cannot stand operational stress may for example cause unexpected hardware problems in the early life of a system. The special session focuses on the first aspect. The first contribution discusses how the interaction with the environment in cyberphysical systems can be appropriately modeled and tested. The second presentation then deals with a cross-layer approach identifying problems at the hardware/software interface which cannot be compensated by the application and must therefore be targeted by specific tests.

Abstract

The accessibility of on-chip embedded infrastructure for test, reconfiguration, or debug poses a serious security problem. Access mechanisms based on IEEE Std 1149.1 (JTAG), and especially reconfigurable scan networks (RSNs), as allowed by IEEE Std 1500, IEEE Std 1149.1-2013, and IEEE Std 1687 (IJTAG), require special care in the design and development. This work studies the threats to trustworthy data transmission in RSNs posed by untrusted components within the RSN and external interfaces. We propose a novel scan pattern generation method that finds trustworthy access sequences to prevent sniffing and spoofing of transmitted data in the RSN. For insecure RSNs, for which such accesses do not exist, we present an automated transformation that improves the security and trustworthiness while preserving the accessibility to attached instruments. The area overhead is reduced based on results from trustworthy access pattern generation. As a result, sensitive data is not exposed to untrusted components in the RSN, and compromised data cannot be injected during trustworthy accesses.

Abstract

Excessive IR-drop during scan shift can cause localized IR-drop around clock buffers and introduce dynamic clock skew. Excessive clock skew at neighboring scan flip-flops results in hold or setup timing violations corrupting test stimuli or test responses during shifting. We introduce a new method to assess the risk of such test data corruption at each scan cycle and flip-flop. The most likely cases of test data corruption are mitigated in a non-intrusive way by selective test data manipulation and masking of affected responses. Evaluation results show the computational feasibility of our method for large benchmark circuits, and demonstrate that a few targeted pattern changes provide large potential gains in shift safety and test time with negligible cost in fault coverage.

Abstract

A large amount of on-chip infrastructure, such as design-for-test, debug, monitoring, or calibration, is required for the efficient manufacturing, debug, and operation of complex hardware systems. The access to such infrastructure poses severe system safety and security threats since it may constitute a side-channel exposing internal state, sensitive data, or IP to attackers. Reconfigurable scan networks (RSNs) have been proposed as a scalable and flexible scan-based access mechanism to on-chip infrastructure. The increasing number and variety of integrated infrastructure as well as diverse access constraints over the system lifetime demand for systematic methods for the specification and formal verification of access protection and security properties in RSNs. This work presents a novel method to specify and verify fine-grained access permissions and restrictions to instruments attached to an RSN. The permissions and restrictions are transformed into predicates that are added to a formal model of a given RSN to prove which access properties hold or do not hold.

Abstract

Delay fault simulation is an essential task during test pattern generation and reliability assessment of electronic circuits. With the high sensitivity of current nano-scale designs towards even smallest delay deviations, the simulation of small gate delay faults has become extremely important. Since these faults have a subtle impact on the timing behavior, traditional fault simulation approaches based on abstract timing models are not sufficient. Furthermore, the detection of these faults is compromised by the ubiquitous variations in the manufacturing processes, which causes the actual fault coverage to vary from circuit instance to circuit instance, and makes the use of timing accurate methods mandatory. However, the application of timing accurate techniques quickly becomes infeasible for larger designs due to excessive computational requirements. In this work, we present a method for fast and waveformaccurate simulation of small delay faults on graphics processing units with exceptional computational performance. By exploiting multiple dimensions of parallelism from gates, faults, waveforms and circuit instances, the proposed approach allows for timing-accurate and exhaustive small delay fault simulation under process variation for designs with millions of gates.

Abstract

Runtime reconfigurable architectures based on Field-Programmable Gate Arrays (FPGAs) allow area- and power-efficient acceleration of complex applications. However, being manufactured in latest semiconductor process technologies, FPGAs are increasingly prone to aging effects, which reduce the reliability and lifetime of such systems. Aging mitigation and fault tolerance techniques for the reconfigurable fabric become essential to realize dependable reconfigurable architectures. This article presents an accelerator diversification method that creates multiple configurations for runtime reconfigurable accelerators that are diversified in their usage of Configurable Logic Blocks (CLBs). In particular, it creates a minimal number of configurations such that all single-CLB and some multi-CLB faults can be tolerated. For each fault we ensure that there is at least one configuration that does not use that CLB. Secondly, a novel runtime accelerator placement algorithm is presented that exploits the diversity in resource usage of these configurations to balance the stress imposed by executions of the accelerators on the reconfigurable fabric. By tracking the stress due to accelerator usage at runtime, the stress is balanced both within a reconfigurable region as well as over all reconfigurable regions of the system. The accelerator placement algorithm also considers faulty CLBs in the regions and selects the appropriate configuration such that the system maintains a high performance in presence of multiple permanent faults. Experimental results demonstrate that our methods deliver up to 3.7x higher performance in presence of faults at marginal runtime costs and 1.6x higher MTTF than state-of-the-art aging mitigation methods.

Abstract

In order to tolerate faults that emerge in operating Networks-on-Chip, diagnosis techniques are employed for fault detection and localization. On various network layers, diverse diagnosis methods can be employed which differ in terms of their impact on network performance (e.g. by operating concurrently vs. pre-empting regular network operation) and the quality of diagnostic results. In this contribution, we show how diagnosis techniques of different network layers of a Network-on-Chip can be combined into multi-layer solutions. We present the cross-layer information flow used for the interaction between the layers and show the resulting benefit of the combination compared to layer-specific diagnosis. For evaluation, we investigate the diagnosis quality and the impact on system performance to explore the entire design space of layer-specific techniques and their multi-layer combinations. We identify pareto-optimal combinations that offer an increase of system performance by a factor of four compared to the single-layer diagnosis.

Abstract

Small delay faults receive more and more attention, since they may indicate a circuit reliability marginality even if they do not violate the timing at the time of production. At-speed test and faster-than-at-speed test (FAST) are rather expensive tasks to test for such faults. The paper at hand avoids complex on-chip structures or expensive high-speed ATE for test response evaluation, if aging monitors which are integrated into the device under test anyway are reused. The main challenge in reusing aging monitors for FAST consists in possible false alerts at higher frequencies. While a certain test vector pair makes a delay fault observable at one monitor, it may also exceed the time slack in the fault free case at a different monitor which has to be masked. Therefore, a multidimensional optimizing problem has to be solved for minimizing the masking overhead and the number of test vectors while maximizing delay fault coverage.

Abstract

With the ever increasing process variability in recent technology nodes, path delay fault testing of digital integrated circuits has become a major challenge. A randomly chosen long path often has no robust test and many of the existing non-robust tests are likely invalidated by process variations. To generate path delay fault tests that are more tolerant towards process variations, the delay test generation must evaluate different non-robust tests and only those tests that sensitize the target path with a sufficiently high probability in presence of process variations must be selected. This requires a huge number of probability computations for a large number of target paths and makes the development of very efficient approximation algorithms mandatory for any practical application. In this paper, a novel and efficient probabilistic sensitization analysis is presented which is used to extract a small subcircuit for a given test vector-pair. The probability that a target path is sensitized by the vector-pair is computed efficiently and without significant error by a Monte-Carlo simulation of the subcircuit.

Abstract

IR-drop induced false capture failures and test clock stretch are severe problems in at-speed scan testing. We propose a new method to efficiently and accurately identify these problems. For the first time, our approach considers the additional dynamic power caused by glitches, the spatial and temporal distribution of all toggles, and their impact on both logic paths and the clock tree without time-consuming electrical simulations.

Abstract

Approximate computing in hardware and software promises significantly improved computational performance combined with very low power and energy consumption. This goal is achieved by both relaxing strict requirements on accuracy and precision, and by allowing a deviating behavior from exact Boolean specifications to a certain extent. Today, approximate computing is often limited to applications with a certain degree of inherent error tolerance, where perfect computational results are not always required. However, in order to fully utilize its benefits, the scope of applications has to be significantly extended to other compute-intensive domains including science and engineering. To meet the often rather strict quality and reliability requirements for computational results in these domains, the use of appropriate characterization and fault tolerance measures is highly required. In this paper, we evaluate some of the available techniques and how they may extend the scope of application for approximate computing.

Abstract

Approximate computing algorithms cover a wide range of different applications and the boundaries to domains like variable-precision computing, where the precision of the computations can be online adapted to the needs of the application 1, 2, as well as probabilistic and stochastic computing 3, which incorporate stochastic processes and probability distributions in the target computations, are sometimes blurred. The central idea of purely algorithm-based approximate computing is to transform algorithms, without necessarily requiring approximate hardware, to trade-off accuracy against energy. Early termination of algorithms that exhibit incremental refinement 4 reduces iterations at the cost of accuracy. Loop perforation 5 approximates iteratively-computed results by identifying and reducing loops that contribute only insignificantly to the solution. Another group of approximate algorithms is represented by neural networks, which can be trained to mimic certain algorithms and to compute approximate results 6. Today, approximate computing is predominantly proposed for applications in multimedia and signal processing with a certain degree of inherent error tolerance. However, in order to fully utilize the benefits of these architectures, the scope of applications has to be significantly extended to other computeintensive tasks, for instance, in science and engineering. Such an extension requires that the allowed error or the required minimum precision of the application is either known beforehand or reliably determined online to deliver trustworthy and useful results. Errors outside the allowed range have to be reliably detected and tackled by appropriate fault tolerance measures.

Abstract

In order to reduce the number of defective parts and increase yield, especially in early stages of production, systematic defects must be identified and corrected as soon as possible. This paper presents a technique to move defect classification to the earliest phase of volume testing without any special diagnostic test patterns. A neural-network-based fault classifier is described, which is able to raise a warning, if the frequency of certain defect mechanisms increases. Only in this case more sophisticated diagnostic patterns or the even more expensive physical failure analysis have to be applied. The fault classification method presented here is able to extract underlying fault types with high confidence by identifying relevant features from the circuit topology and from logic simulation.

Abstract

We propose a fault tolerance approach for sparse matrix operations that detects and implicitly locates errors in the results for efficient local correction. This approach reduces the runtime overhead for fault tolerance and provides high error coverage. Existing algorithm-based fault tolerance approaches for sparse matrix operations detect and correct errors, but they often rely on expensive error localization steps. General checkpointing schemes can induce large recovery cost for high error rates. For sparse matrix-vector multiplications, experimental results show an average reduction in runtime overhead of 43.8%, while the error coverage is on average improved by 52.2% compared to related work. The practical applicability is demonstrated in a case study using the iterative Preconditioned Conjugate Gradient solver. When scaling the error rate by four orders of magnitude, the average runtime overhead increases only by 31.3% compared to low error rates.

Abstract

Unknown (X) values in a design introduce pessimism in conventional test generation algorithms which results in a loss of fault coverage. This pessimism is reduced by a more accurate modeling and analysis. Unfortunately, accurate analysis techniques highly increase runtime and limit scalability. One promising technique to prevent high runtimes while still providing high accuracy is the use of restricted symbolic logic (RSL). However, also pure RSL-based algorithms reach their limits as soon as millon gate circuits need to be processed. In this paper, we propose new ATPG techniques to overcome such limitations. An efficient hybrid encoding combines the accuracy of RSL-based modeling with the compactness of conventional threevalued encoding. A low-cost two-valued SAT-based untestability check is able to classify most untestable faults with low runtime. An incremental and event-based accurate fault simulator is introduced to reduce fault simulation effort. The experiments demonstrate the effectiveness of the proposed techniques. Over 97% of the faults are accurately classified. Both the number of aborts and the total runtime are significantly reduced compared to the state-of-the-art pure RSL-based algorithm. For circuits up to a million gates, the fault coverage could be increased considerably compared to a state-of-the-art commercial tool with very competitive runtimes.

Abstract

A new technique is presented that allows to execute the preconditioned conjugate gradient (PCG) solver on approximate hardware while ensuring correct solver results. This technique expands the scope of approximate computing to scientific and engineering applications. The changing error resilience of PCG during the solving process is exploited by different levels of approximation which trade off numerical accuracy and hardware utilization. Such approximation levels are determined at runtime by periodically estimating the error resilience. An efficient fault tolerance technique allows reductions in hardware utilization by ensuring the continued exploitation of maximum allowed energy-accuracy trade-offs. Experimental results show that the hardware utilization is reduced on average by 14.5% and by up to 41.0% compared to executing PCG on accurate hardware.

Abstract

Das Projekt ”SHIVA: Sichere Hardware in der Informationsverarbeitung“ ist Teil des Forschungsprogramms ”IKTSicherheit für weltweit vernetzte vertrauenswürdige Infrastrukturen“ der Baden-Württemberg Stiftung. Ziel des Projekts sind die Erforschung von Entwurfs- und Verifikationsmethoden zur Steigerung der Sicherheit mikroelektronischer Hardware, beispielsweise aus der Automobilelektronik, der Medizintechnik oder auch der Fertigungstechnik. Es soll damit die missbräuchliche Verwendung nicht-funktionaler Hardware-Infrastruktur zur Beobachtung interner sensibler Daten, verwendeter Verfahren und Prozesse sowie zu Angriffen auf das geistige Eigentum an der Hardware ausgeschlossen werden. Das Projekt ist eine Kooperation des Instituts für Technische Informatik (ITI) der Universität Stuttgart und des Lehrstuhls für Rechnerarchitektur der Universität Freiburg. Dieser Beitrag stellt die Projektziele und erste Forschungsergebnisse vor.

Abstract

On-chip infrastructure is an essential part of today’s complex designs and enables their cost-efficient manufacturing and operation. The diversity and high number of infrastructure elements demands flexible and low-latency access mechanisms, such as reconfigurable scan networks (RSNs). The correct operation of the infrastructure access itself is highly important for the test of the system logic, its diagnosis, debug and bring-up, as well as post-silicon validation. Ensuring correct operation requires the thorough testing of the RSN. Because of sequential and combinational dependencies in RSN accesses, test generation for general RSNs is computationally very difficult and requires dedicated test strategies. This paper explores different test strategies for general RSNs and discusses the achieved structural fault coverage. Experimental results show that the combination of functional test heuristics together with a dedicated RSN test pattern generation approach significantly outperforms the test quality of a standard ATPG tool.

Abstract

Deviations in the first-order parameters of CMOS cells can lead to severe errors in the functional and time domain. With increasing sensitivity of these parameters to manufacturing defects and variation, parametric and parasitic-aware fault simulation is becoming crucial in order to support test pattern generation. Traditional approaches based on gate-level models are not sufficient to represent and capture the impact of deviations in these parameters in either an efficient or accurate manner. Evaluation at electrical level, on the other hand, severely lacks execution speed and quickly becomes inapplicable to larger designs due to high computational demands. This work presents a novel fault simulation approach considering first-order parameters in CMOS circuits to explicitly capture CMOS-specific behavior in the functional and time domain with transistor granularity. The approach utilizes massive parallelization in order to achieve high-throughput acceleration on Graphics Processing Units (GPUs) by exploiting parallelism of cells, stimuli and faults. Despite the more precise level of abstraction, the simulator is able to process designs with millions of gates and even outperforms conventional simulation at logic level in terms of modeling accuracy and simulation speed.

Abstract

Today's MPSOCs employ complex on-chip infrastructure and instrumentation for efficient test, debug, diagnosis, and post-silicon validation, reliability management and maintenance in the field, or monitoring and calibration during operation. To enable flexible and efficient access to such instrumentation, reconfigurable scan networks (RSNs) as recently standardized by IEEE Std 1687 can be used. Given the importance of infrastructure for the dependability of the whole MPSOC, however, the RSN itself must be highly dependable. This paper addresses dependability issues of RSNs including verification, test, and security, and their importance for dependable MPSOCs. First research results are summarized, and open questions for future work are highlighted.

Abstract

Reconfigurable Networks-on-Chip (NoCs) allow discarding the corrupted ports of a defective switch instead of deactivating it entirely, and thus enable fine-grained reconfiguration of the network, making the NoC structures more robust. A prerequisite for such a fine-grained reconfiguration is to identify the corrupted port of a faulty switch. This paper presents a functional diagnosis approach which extracts structural fault information from functional tests and utilizes this information to identify the broken functions/ports of a defective switch. The broken parts are discarded while the remaining functions are used for the normal operation. The non-intrusive method introduced is independent of the switch architecture and the NoC topology and can be applied for any type of structural fault. The i diagnostic resolution of the functional test is so high that for nearly 64% of the faults in the example switch only a single port has to be switched off. As the remaining parts stay completely functional, the impact of faults on throughput and performance is minimized.

Abstract

IEEE Std. 1687, or IJTAG, defines flexible serial scan-based architectures for accessing embedded instruments efficiently. In this paper, we present a novel test architecture that employs IEEE Std. 1687 together with an efficient test controller to carry out 3D-IC testing autonomously. The test controller can deliver parallel test data for the IEEE Std. 1687 structures and the cores under test, and provide required control signals to control the whole test procedure. This design can achieve at-speed, autonomous and programmable testing in 3D-ICs. Experimental results show that the additional area and test cycle overhead of this architecture is small considering its autonomous test capability.

Abstract

Reconfigurable scan networks (RSN) as standardized by IEEE Std 1687 allow flexible and efficient access to on-chip infrastructure for test and diagnosis, post-silicon validation, debug, bring-up, or maintenance in the field. However, unauthorized access or manipulation of the attached instruments, monitors, or controllers pose security and safety risks. Different RSN architectures have recently been proposed to implement secure access to the connected instruments, for instance by authentication and authorization. To ensure that the implemented security schemes cannot be bypassed, design verification of the security properties is mandatory. However, combinational and deep sequential dependencies of modern RSNs and their extensions for security require novel approaches to formal verification for unbounded model checking. This work presents for the first time a formal design verification methodology for security properties of RSNs based on unbounded model checking that is able to verify access protection at logical level. Experimental results demonstrate that state-of-the-art security schemes for RSNs can be efficiently handled, even for very large designs.

Abstract

The simulation of delay faults is an essential task in design validation and reliability assessment of circuits. Due to the high sensitivity of current nano-scale designs against smallest delay deviations, small delay faults recently became the focus of test research. Because of the subtle delay impact, traditional fault simulation approaches based on abstract timing models are not sufficient for representing small delay faults. Hence, timing accurate simulation approaches have to be utilized, which quickly become inapplicable for larger designs due to high computational requirements. In this work we present a waveform-accurate approach for fast high-throughput small delay fault simulation on Graphics Processing Units (GPUs). By exploiting parallelism from gates, faults and patterns, the proposed approach enables accurate exhaustive small delay fault simulation even for multi-million gate designs without fault dropping for the first time.

Abstract

IR-drop induced by launch switching activity (LSA) in capture mode during at-speed scan testing increases delay along not only logic paths (LPs) but also clock paths (CPs). Excessive extra delay along LPs compromises test yields due to false capture failures, while excessive extra delay along CPs compromises test quality due to test clock stretch. This paper is the first to mitigate the impact of LSA on both LPs and CPs with a novel LCPA (Logic/Clock-Path-Aware) at-speed scan test generation scheme, featuring (1) a new metric for assessing the risk of false capture failures based on the amount of LSA around both LPs and CPs, (2) a procedure for avoiding false capture failures by reducing LSA around LPs or masking uncertain test responses, and (3) a procedure for reducing test clock stretch by reducing LSA around CPs. Experimental results demonstrate the effectiveness of the LCPA scheme in improving test yields and test quality.

Abstract

Small gate delay faults (SDFs) are not detectable at-speed, if they can only be propagated along short paths. These hidden delay faults (HDFs) do not influence the circuit’s behavior initially, but they may indicate design marginalities leading to early-life failures, and therefore they cannot be neglected. HDFs can be detected by faster-than-at-speed test (FAST), where typically several different frequencies are used to maximize the coverage. A given set of test patterns P potentially detects a HDF if it contains a test pattern sensitizing a path through the fault site, and the efficiency of FAST can be measured as the ratio of actually detected HDFs to potentially detected HDFs. The paper at hand targets maximum test efficiency with a minimum number of frequencies. The procedure starts with a test set for transition delay faults and a set of preselected equidistant frequencies. Timing-accurate simulation of this initial setup identifies the hard-to-detect faults, which are then targeted by a more complex timing-aware ATPG procedure. For the yet undetected HDFs, a minimum number of frequencies are determined using an efficient hypergraph algorithm. Experimental results show that with this approach, the number of test frequencies required for maximum test efficiency can be reduced considerably. Furthermore, test set inflation is limited as timing-aware ATPG is only used for a small subset of HDFs.

Abstract

Unknown (X) values emerge during the design process as well as during system operation and test application. X-sources are for instance black boxes in design models, clockdomain boundaries, analog-to-digital converters, or uncontrolled or uninitialized sequential elements. To compute a test pattern for a given fault, well-defined logic values are required both for fault activation and propagation to observing outputs. In presence of X-values, conventional test generation algorithms, based on structural algorithms, Boolean satisfiability (SAT), or BDD-based reasoning may fail to generate test patterns or to prove faults untestable. This work proposes the first efficient stuck-at and transitiondelay fault test generation algorithm able to prove testability or untestability of faults in presence of X-values. It overcomes the principal pessimism of conventional algorithms when X-values are considered by mapping the test generation problem to the satisfiability of Quantified Boolean Formulae (QBF). Experiments on ISCAS benchmarks and larger industrial circuits investigate the increase in fault coverage for conventional deterministic and potential detection requirements for both randomized and clustered X-sources.

Abstract

Achieving system-level dependability is a demanding task. The manifold requirements and dependability threats can no longer be statically addressed at individual abstraction layers. Instead, all components of future multi-processor systems-on-chip (MPSoCs) have to contribute to this common goal in an adaptive manner. In this paper we target a generic heterogeneous MPSoC that combines general purpose processors along with dedicated application-specific hard-wired accelerators, fine-grained reconfigurable processors, and coarse-grained reconfigurable architectures. We present different reactive and proactive measures at the layers of the runtime system (online resource management), system architecture (global communication), micro architecture (individual tiles), and gate netlist (tile-internal circuits) to address dependability threats.

Abstract

Many EDA tasks like test set characterization or the precise estimation of power consumption, power droop and temperature development, require a very large number of time-aware gate-level logic simulations. Until now, such characterizations have been feasible only for rather small designs or with reduced precision due to the high computational demands. The new simulation system presented here is able to accelerate such tasks by more than two orders of magnitude and provides for the first time fast and comprehensive timing simulations for industrial-sized designs. Hazards, pulse-filtering, and pin-to-pin delay are supported for the first time in a GPGPU accelerated simulator, and the system can easily be extended to even more realistic delay models and further applications. A sophisticated mapping with efficient memory utilization and access patterns as well as minimal synchronizations and control flow divergence is able to use the full potential of GPGPU architectures. To provide such a mapping, we combine for the first time the versatility of event-based timing simulation and multidimensional parallelism used in GPU-based gate-level simulators. The result is a throughput-optimized timing simulation algorithm, which runs many simulation instances in parallel and at the same time fully exploits gate-parallelism within the circuit.

Abstract

Die Simulation kleiner Verzögerungsfehler ist ein wichtiger Bestandteil der Validierung nano-elektronischer Schaltungen. Prozessvariationen während der Herstellung haben großen Einfluss auf die Erkennung dieser Fehler und müssen bei der Simulation berücksichtigt werden. Die zeitgenaue Simulation von Verzögerungsfehlern ist verglichen mit traditioneller Logiksimulation oder statischer Zeitanalyse sehr aufwändig und die Rechenkomplexität steigt durch die Berücksichtigung von Variationen zusätzlich an. In dieser Arbeit wird ein hochparalleles Verfahren vorgestellt, welches Grafikprozessoren zur beschleunigten parallelen Simulation kleiner Verzögerungsfehler unter Variation anwendet. Das Verfahren berechnet akkurate Signalverläufe in der Schaltung und ermöglicht die Bestimmung einer Monte-Carlo-basierten statistischen Fehlererfassung für industrielle Schaltkreise unter zufälliger sowie systematischer Variation.

Abstract

Linear system solvers are an integral part for many different compute-intensive applications and they benefit from the compute power of heterogeneous computer architectures. However, the growing spectrum of reliability threats for such nano-scaled CMOS devices makes the integration of fault tolerance mandatory. The preconditioned conjugate gradient (PCG) method is one widely used solver as it finds solutions typically faster compared to direct methods. Although this iterative approach is able to tolerate certain errors, latest research shows that the PCG solver is still vulnerable to transient effects. Even single errors, for instance, caused by marginal hardware, harsh environments, or particle radiation, can considerably affect execution times, or lead to silent data corruption. In this work, a novel fault-tolerant PCG solver with extremely low runtime overhead is proposed. Since the error detection method does not involve expensive operations, it scales very well with increasing problem sizes. In case of errors, the method selects between three different correction methods according to the identified error. Experimental results show a runtime overhead for error detection ranging only from 0.04% to 1.70%.

Abstract

Aging effects in nano-scale CMOS circuits impair the reliability and Mean Time to Failure (MTTF) of embedded systems. Especially for FPGAs that are manufactured in the latest technology node, aging is a major concern. We introduce the first cross-layer aging-aware placement method for accelerators in FPGA-based runtime reconfigurable architectures. It optimizes stress distribution by accelerator placement at runtime, i.e. to which reconfigurable region an accelerator shall be reconfigured. Additionally, it optimizes logic placement at synthesis time to diversify the resource usage of individual accelerators, i.e. which CLBs of a reconfigurable region shall be used by an accelerator. Both layers together balance the intra- and inter-region stress induced by the application workload at negligible performance cost. Experimental results show significant reduction of maximum stress of up to 64% and 35%, which leads to up to 177% and 14% MTTF improvement relative to state-of- the-art methods w.r.t. HCI and BTI aging, respectively.

Abstract

Linear system solvers are key components of many scientific applications and they can benefit significantly from modern heterogeneous computer architectures. However, such nano-scaled CMOS devices face an increasing number of reliability threats, which make the integration of fault tolerance mandatory. The preconditioned conjugate gradient method (PCG) is a very popular solver since it typically finds solutions faster than direct methods, and it is less vulnerable to transient effects. However, as latest research shows, the vulnerability is still considerable. Even single errors caused, for instance, by marginal hardware, harsh operating conditions or particle radiation can increase execution times considerably or corrupt solutions without indication. In this work, a novel and highly efficient fault-tolerant PCG method is presented. The method applies only two inner products to reliably detect errors. In case of errors, the method automatically selects between roll-back and efficient on-line correction. This significantly reduces the error detection overhead and expensive re-computations.

Abstract

Efficient access to on-chip instrumentation is a key requirement for post-silicon validation, test, debug, bringup, and diagnosis. Reconfigurable scan networks, as proposed by e.g. IEEE P1687 and IEEE Std 1149.1-2013, emerge as an effective and affordable means to cope with the increasing complexity of on-chip infrastructure. Reconfigurable scan networks are often hierarchical and may have complex structural and functional dependencies. Common approaches for scan verification based on static structural analysis and functional simulation are not sufficient to ensure correct operation of these types of architectures. To access an instrument in a reconfigurable scan network, a scan-in bit sequence must be generated according to the current state and structure of the network. Due to sequential and combinational dependencies, the access pattern generation process (pattern retargeting) poses a complex decision and optimization problem. This article presents the first generalized formal model that considers structural and functional dependencies of reconfigurable scan networks and is directly applicable to P1687-based and 1149.1-2013-based scan architectures. This model enables efficient formal verification of complex scan networks, as well as automatic generation of access patterns. The proposed pattern generation method supports concurrent access to multiple target scan registers (access merging) and generates short scan-in sequences.

Abstract

Circuit aging causes a performance degradation and eventually a functional failure. It depends on the workload and the environmental condition of the system, which are hard to predict in early design phases resulting in pessimistic worst case design. Existing delay monitoring schemes measure the remaining slack of paths in the circuit, but cause a significant hardware penalty including global wiring. More importantly, the low sensitization ratio of long paths in applications may lead to a very low measurement frequency or even an unmonitored timing violation. In this work, we propose a delay monitor placement method by analyzing the topological circuit structure and sensitization of paths. The delay monitors are inserted at meticulously selected positions in the circuit, named observation points (OPs). This OP monitor placement method can reduce the number of inserted monitors by up to 98% compared to a placement at the end of long paths. The experimental validation shows the effectiveness of this aging indication, i.e. a monitor issues a timing alert always earlier than any imminent timing failure.

Abstract

Nanoscale technologies are increasingly susceptible to aging processes such as Negative-Bias Temperature Instability (NBTI) which undermine the reliability of VLSI systems. Existing monitoring techniques can detect the violation of safety margins and hence make the prediction of an imminent failure possible. However, since such techniques can only detect measurable degradation effects which appear after a relatively long period of system operation, they are not well suited to early aging prediction and proactive aging alleviation. This work presents a novel method for the monitoring of NBTI-induced degradation rate in digital circuits. It enables the timely adoption of proper mitigation techniques that reduce the impact of aging. The developed method employs machine learning techniques to find a small set of so called Representative Critical Gates (RCG), the workload of which is correlated with the degradation of the entire circuit. The workload of RCGs is observed in hardware using so called workload monitors. The output of the workload monitors is evaluated on-line to predict system degradation experienced within a configurable (short) period of time, e.g. a fraction of a second. Experimental results show that the developed monitors predict the degradation rate with an average error of only 1.6% at 4.2% area overhead.

Abstract

Failure diagnosis of field returns typically requires high quality test stimuli and assumes that tests can be repeated. For intermittent faults with fault activation conditions depending on the physical environment, the repetition of tests cannot ensure that the behavior in the field is also observed during diagnosis, causing field returns diagnosed as no-trouble-found. In safety critical applications, self-checking circuits, which provide concurrent error detection, are frequently used. To diagnose intermittent and transient faulty behavior in such circuits, we use the stored encoded circuit outputs in case of a failure (called signatures) for later analysis in diagnosis. For the first time, a diagnosis algorithm is presented that is capable of performing the classification of intermittent or transient faults using only the very limited amount of functional stimuli and signatures observed during operation and stored on chip. The experimental results demonstrate that even with these harsh limitations it is possible to distinguish intermittent from transient faulty behavior. This is essential to determine whether a circuit in which failures have been observed should be subject to later physical failure analysis, since intermittent faulty behavior has been diagnosed. In case of transient faulty behavior, it may still be operated reliably.

Abstract

Modern VLSI designs incorporate a high amount of instrumentation that supports post-silicon validation and debug, volume test and diagnosis, as well as in-field system monitoring and maintenance. Reconfigurable scan architectures, as allowed by the novel IEEE Std 1149.1-2013 (JTAG) and IEEE Std 1687- 2014 (IJTAG), emerge as a scalable mechanism for access to such on-chip instruments. While the on-chip instrumentation is crucial for meeting quality, dependability, and time-to-market goals, it is prone to abuse and threatens system safety and security. A secure access management method is mandatory to assure that critical instruments be accessible to authorized entities only. This work presents a novel protection method for fine-grained access management in complex reconfigurable scan networks based on a challenge-response authentication protocol. The target scan network is extended with an authorization instrument and Secure Segment Insertion Bits (S²IB) that together control the accessibility of individual instruments. To the best of the authors’ knowledge, this is the first fine-grained access management scheme that scales well with the number of protected instruments and offers a high level of security. Compared with recent stateof- the-art techniques, this scheme is more favorable with respect to implementation cost, performance overhead, and provided security level.

Abstract

Computational biology contributes important solutions for major biological challenges. Unfortunately, most applications in computational biology are highly computeintensive and associated with extensive computing times. Biological problems of interest are often not treatable with traditional simulation models on conventional multi-core CPU systems. This interdisciplinary work introduces a new multi-timescale simulation model for apoptotic receptor-clustering and a new parallel evaluation algorithm that exploits the computational performance of heterogeneous CPU-GPU computing systems. For this purpose, the different dynamics involved in receptor-clustering are separated and simulated on two timescales. Additionally, the time step sizes are adaptively refined on each timescale independently. This new approach improves the simulation performance significantly and reduces computing times from months to hours for observation times of several seconds.

Abstract

With increasing transient error rates, distinguishing intermittent and transient faults is especially challenging. In addition to particle strikes relatively high transient error rates are observed in architectures for opportunistic computing and in technologies under high variations. This paper presents a method to classify faults into permanent, intermittent and transient faults based on some intermediate signatures during embedded test or built-in self-test. Permanent faults are easily determined by repeating test sessions. Intermittent and transient faults can be identified by the amount of failing test sessions in many cases. For the remaining faults, a Bayesian classification technique has been developed which is applicable to large digital circuits. The combination of these methods is able to identify intermittent faults with a probability of more than 98 %.

Abstract

Soft errors are a reliability threat for reconfigurable systems implemented with SRAM-based FPGAs. They can be handled through fault tolerance techniques like scrubbing and modular redundancy. However, selecting these techniques statically at design or compile time tends to be pessimistic and prohibits optimal adaptation to changing soft error rate at runtime. We present the GUARD method which allows for autonomous runtime reliability management in reconfigurable architectures: Based on the error rate observed during runtime, the runtime system dynamically determines whether a computation should be executed by a hardened processor, or whether it should be accelerated by inherently less reliable reconfigurable hardware which can trade-off performance and reliability. GUARD is the first runtime system for reconfigurable architectures that guarantees a target reliability while optimizing the performance. This allows applications to dynamically chose the desired degree of reliability. Compared to related work with statically optimized fault tolerance techniques, GUARD provides up to 68.3% higher performance at the same target reliability.

Abstract

Scan infrastructures based on IEEE Std. 1149.1 (JTAG), 1500 (SECT), and P1687 (IJTAG) provide a cost-effective access mechanism for test, reconfiguration, and debugging purposes. The improved accessibility of on-chip instruments, however, poses a serious threat to system safety and security. While state-of-theart protection methods for scan architectures compliant with JTAG and SECT are very effective, most of these techniques face scalability issues in reconfigurable scan networks allowed by the upcoming IJTAG standard. This paper describes a scalable solution for multilevel access management in reconfigurable scan networks. The access to protected instruments is restricted locally at the interface to the network. The access restriction is realized by a sequence filter that allows only a precomputed set of scan-in access sequences. This approach does not require any modification of the scan architecture and causes no access time penalty. Therefore, it is well suited for core-based designs with hard macros and 3D integrated circuits. Experimental results for complex reconfigurable scan networks show that the area overhead depends primarily on the number of allowed accesses, and is marginal even if this number exceeds the count of registers in the network.

Abstract

This paper introduces a hybrid method to synthesize area-efficient fault-secure NoC switches to detect all errors resulting from any single-point combinational or transition fault in switches and interconnect links. Firstly, the structural faults that are always detectable by data encoding at flit-level are identified. Next, the fault-secure structure is constructed with minimized area such that errors caused by the remaining faults are detected under any given input vector. The experimental evaluation shows significant area savings compared to conventional fault-secure schemes. In addition, the resulting structure can be reused for test compaction. This reduces the amount of test response data and test time without loss of fault coverage or diagnostic resolution.

Abstract

Gate-level timing simulation of combinational CMOS circuits is the foundation of a whole array of important EDA tools such as timing analysis and power-estimation, but the demand for higher simulation accuracy drastically increases the runtime complexity of the algorithms. Data-parallel accelerators such as Graphics Processing Units (GPUs) provide vast amounts of computing performance to tackle this problem, but require careful attention to control-flow and memory access patterns. This paper proposes the novel High-Throughput Oriented Parallel Switch-level Simulator (HiTOPS), which is especially designed to take full advantage of GPUs and provides accurate time- simulation for multi-million gate designs at an unprecedented throughput. HiTOPS models timing at transistor granularity and supports all major timing-related effects found in CMOS including pattern-dependent delay, glitch filtering and transition ramps, while achieving speedups of up to two orders of magnitude compared to traditional gate-level simulators.

Abstract

With ever more complex automotive systems, the current approach of using functional tests to locate faulty components results in very long analysis procedures and poor diagnostic accuracy. Built-In Self-Test (BIST) offers a promising alternative to collect structural diagnostic information during E/E-architecture test. However, as the automotive industry is quite cost-driven, structural diagnosis shall not deteriorate traditional design objectives. With this goal in mind, the work at hand proposes a design space exploration to integrate structural diagnostic capabilities into an E/E-architecture design. The proposed integration is performed non-intrusively, i. e., the addition and execution of tests (a) does not affect any functional applications and (b) does not require any costly changes in the communication schedules.

Abstract

Software-Based Self-Test (SBST) is extended to the switches of complex Network-on-Chips (NoC). Test patterns for structural faults are turned into valid packets by using satisfiability (SAT) solvers. The test technique provides a high fault coverage for both manufacturing test and online test.

Abstract

Logic and fault simulation are essential techniques in electronic design automation. The accuracy of standard simulation algorithms is compromised by unknown or X-values. This results in a pessimistic overestimation of X-valued signals in the circuit and a pessimistic underestimation of fault coverage. This work proposes efficient algorithms for combinational and sequential logic as well as for stuck-at and transition-delay fault simulation that are free of any simulation pessimism in presence of unknowns. The SAT-based algorithms exactly classifiy all signal states. During fault simulation, each fault is accurately classified as either undetected, definitely detected, or possibly detected. The pessimism with respect to unknowns present in classic algorithms is thoroughly investigated in the experimental results on benchmark circuits. The applicability of the proposed algorithms is demonstrated on larger industrial circuits. The results show that, by accurate analysis, the number of detected faults can be significantly increased without increasing the test-set size.

Abstract

This survey introduces into the common practices, current challenges and advanced techniques of high quality system level test and diagnosis. Specialized techniques and industrial standards of testing complex boards are introduced. The reuse for system test of design for test structures and test data developed at chip level is discussed, including the limitations and research challenges. Structural test methods have to be complemented by functional test methods. State-of-the-art and leading edge research for functional testing will be covered.

Abstract

This paper presents a new hybrid fault-tolerant architecture for robustness improvement of digital CMOS circuits and systems. It targets all kinds of errors in combinational part of logic circuits and thus, can be combined with advanced SEU protection techniques for sequential elements while reducing the power consumption. The proposed architecture combines different types of redundancies: information redundancy for error detection, temporal redundancy for soft error correction and hardware redundancy for hard error correction. Moreover, it uses a pseudo-dynamic comparator for SET and timing errors detection. Besides, the proposed method also aims to reduce power consumption of fault-tolerant architectures while keeping a comparable area overhead compared to existing solutions. Results on the largest ISCAS'85 and ITC'99 benchmark circuits show that our approach has an area cost of about 3 % to 6 % with a power consumption saving of about 33 % compared to TMR architectures.

Abstract

As the technology shrinks, nonfunctional properties (NFPs) such as reliability, vulnerability, power consumption, or heat dissipation become as important as system functionality. As NFPs often influence each other, depend on the application and workload of a system, and exhibit nonlinear behavior, NFP simulation over long periods of system operation is computationally expensive, if feasible at all. This article presents a piecewise evaluation method for efficient NFP simulation. Simulation time is divided into intervals called evaluation windows, within which the NFP models are partially linearized. High-speed functional system simulation is achieved by parallel execution of models at different levels of abstraction. A trade-off between simulation speed and accuracy is met by adjusting the size of the evaluation window. As an example, the piecewise evaluation technique is applied to analyze aging caused by two mechanisms, namely Negative Bias Temperature Instability (NBTI) and Hot Carrier Injection (HCI), in order to identify reliability hotspots. Experiments show that the proposed technique yields considerable simulation speedup at a marginal loss of accuracy.

Abstract

The Resilience Articulation Point (RAP) model aims at provisioning researchers and developers with a probabilistic fault abstraction and error propagation framework covering all hardware/software layers of a System on Chip. RAP assumes that physically induced faults at the technology or CMOS device layer will eventually manifest themselves as a single or multiple bit flip(s). When probabilistic error functions for specific fault origins are known at the bit or signal level, knowledge about the unit of design and its environment allow the transformation of the bit-related error functions into characteristic higher layer representations, such as error functions for data words, Finite State Machine (FSM) state, macro-interfaces or software variables. Thus, design concerns at higher abstraction layers can be investigated without the necessity to further consider the full details of lower levels of design. This paper introduces the ideas of RAP based on examples of radiation induced soft errors in SRAM cells, voltage variations and sequential CMOS logic. It shows by example how probabilistic bit flips are systematically abstracted and propagated towards higher abstraction levels up to the application software layer, and how RAP can be used to parameterize architecture-level resilience methods.

Abstract

The constantly growing amount of semiconductors in automotive systems increases the number of possible defect mechanisms, and therefore raises also the effort to maintain a sufficient level of quality and reliability. A promising solution to this problem is the on-line application of structural tests in key components, typically ECUs. In this work, an approach for the optimized integration of both Software-Based Self-Tests (SBST) and Built-In Self-Tests (BIST) into E/E architectures is presented. The approach integrates the execution of the tests non-intrusively, i. e., it (a) does not affect functional applications and (b) does not require costly changes in the communication schedules or additional communication overhead. Via design space exploration, optimized implementations with respect to multiple conflicting objectives, i. e., monetary costs, safety, test quality, and required execution time are derived.

Abstract

Rekonfigurierbare Scan-Netze, z. B. entsprechend IEEE Std. P1687 oder 1149.1-2013, ermöglichen den effizienten Zugriff auf On-Chip-Infrastruktur für Bringup, Debug, Post-Silicon-Validierung und Diagnose. Diese Scan-Netze sind oft hierarchisch und können komplexe strukturelle und funktionale Abhängigkeiten aufweisen. Bekannte Verfahren zur Verifikation von Scan-Ketten, basierend auf Simulation und struktureller Analyse, sind nicht geeignet, Korrektheitseigenschaften von komplexen Scan-Netzen zu verifizieren. Diese Arbeit stellt ein formales Modell für rekonfigurierbare Scan-Netze vor, welches die strukturellen und funktionalen Abhängigkeiten abbildet und anwendbar ist für Architekturen nach IEEE P1687. Das Modell dient als Grundlage für effizientes Bounded Model Checking von Eigenschaften, wie z. B. der Erreichbarkeit von Scan-Registern.

Abstract

Small delay faults may be an indicator of a reliability threat, even if they do not affect the system functionality yet. In recent years, Faster-than-at-Speed-Test (FAST) has become a feasible method to detect faults, which are hidden by the timing slack or by long critical paths in the combinational logic. FAST poses severe challenges to the automatic test equipment with respect to timing, performance, and resolution. In this paper, it is shown how logic built-in self-test (BIST) or embedded deterministic test can be used for an efficient FAST application. Running BIST just at a higher frequency is not an option, as outputs of long paths will receive undefined values due to set time violations and destroy the content of the signature registers. Instead, for a given test pattern sequence, faults are classified according to the optimal detection frequency. For each class, a MISR-based compaction scheme is adapted, such that the critical bits to be observed can be determined by algebraic computations. Experiments show that rather a small number of inter-mediate signatures have to be evaluated to observe a large fraction of hidden delay faults testable by the given test sequence.

Abstract

Large process variations in recent technology nodes present a major challenge for the timing analysis of digital integrated circuits. The optimization decisions of a statistical delay test generation method must therefore rely on the probability of detecting a target delay fault with the currently chosen test vector pairs. However, the huge number of probability evaluations in practical applications creates a large computational overhead. To address this issue, this paper presents the first incremental delay fault detection probability computation algorithm in the literature, which is suitable for the inner loop of automatic test pattern generation methods. Compared to Monte Carlo simulations of NXP benchmark circuits, the new method consistently shows a very large speedup and only a small approximation error.

Abstract

Defects cluster, and the probability of a multiple fault is significantly higher than just the product of the single fault probabilities. While this observation is beneficial for high yield, it complicates fault diagnosis. Multiple faults will occur especially often during process learning, yield ramp-up and field return analysis. In this paper, a logic diagnosis algorithm is presented which is robust against multiple faults and which is able to diagnose multiple faults with high accuracy even on compressed test responses as they are produced in embedded test and built-in self-test. The developed solution takes advantage of the linear properties of a MISR compactor to identify a set of faults likely to produce the observed faulty signatures. Experimental results show an improvement in accuracy of up to 22 % over traditional logic diagnosis solutions suitable for comparable compaction ratios.

Abstract

To cope with the problems of technology scaling, a robust design has become desirable. Self-checking circuits combined with rollback or repair strategies can provide a low cost solution for many applications. However, standard synthesis procedures may violate design constraints or lead to sub-optimal designs. The SAT-based strategies for the verification and synthesis of self-checking circuits presented in this paper can provide efficient solutions.

Abstract

General-purpose computations on graphics processing units (GPUs) enable large-scale scientific applications and simulations on the desktop. Such applications typically have high performance and reliability requirements. For GPUs, which are still designed for the graphics mass-market, hardware-based fault tolerance measures often do not have the highest priority, which makes the application of appropriate software-based fault tolerance mandatory. Algorithm-based Fault Tolerance (ABFT) allows the efficient and effective protection of important kernels from scientific computing. Some ABFT schemes have already been adapted for GPU architectures. However, due to roundoff error introduced by floating-point arithmetic, ABFT requires the determination of tight error bounds for the error detection. The determination of such error bounds is a highly challenging task. In this work, we introduce A-ABFT for GPUs, a new parallel ABFT scheme that determines appropriate error bounds for the checksum comparison step autonomously and which therefore enables the transparent operation of ABFT without any user interaction.

Abstract

Test generation algorithms based on standard n-valued logic algebras are pessimistic in presence of unknown (X) values, overestimate the number of signals with X-values and underestimate fault coverage. Recently, an ATPG algorithm based on quantified Boolean formula (QBF) has been presented, which is accurate in presence of X-values but has limits with respect to runtime, scalability and robustness. In this paper, we consider ATPG based on restricted symbolic logic (RSL) and demonstrate its potential. We introduce a complete RSL ATPG exploiting the full potential of RSL in ATPG. Experimental results demonstrate that RSL ATPG significantly increases fault coverage over classical algorithms and provides results very close to the accurate QBF-based algorithm. An optimized version of RSL ATPG (together with accurate fault simulation) is up to 618x faster than the QBF-based solution, more scalable and more robust.

Abstract

Test is an essential task since the early days of digital circuits. Every produced chip undergoes at least a production test supported by on-chip test infrastructure to reduce test cost. Throughout the technology evolution fault tolerance gained importance and is now necessary in many applications to mitigate soft errors threatening consistent operation. While a variety of effective solutions exists to tackle both areas, test and fault tolerance are often implemented orthogonally, and hence do not exploit the potential synergies of a combined solution. The unified architecture presented here facilitates fault tolerance and test by combining a checksum of the sequential state with the ability to flip arbitrary bits. Experimental results confirm a reduced area overhead compared to a orthogonal combination of classical test and fault tolerance schemes. In combination with heuristically generated test sequences the test application time and test data volume are reduced significantly.

Abstract

Graphics processing units (GPUs) enable large-scale scientific applications and simulations on the desktop. To allow scientific computing on GPUs with high performance and reliability requirements, the application of software-based fault tolerance is attractive. Algorithm-Based Fault Tolerance (ABFT) protects important scientific operations like matrix multiplications. However, the application to floating-point operations necessitates the runtime classification of errors into inevitable rounding errors, allowed compute errors in the magnitude of such rounding errors, and into critical errors that are larger than those and not tolerable. Hence, an ABFT scheme needs suitable rounding error bounds to detect errors reliably. The determination of such error bounds is a highly challenging task, especially since it has to be integrated tightly into the algorithm and executed autonomously with low performance overhead. In this work, A-ABFT for matrix multiplications on GPUs is introduced, which is a new, parallel ABFT scheme that determines rounding error bounds autonomously at runtime with low performance overhead and high error coverage.

Abstract

Unknown (X) values may emerge during the design process as well as during system operation and test application. Sources of X-values are for example black boxes, clockdomain boundaries, analog-to-digital converters, or uncontrolled or uninitialized sequential elements. To compute a detecting pattern for a given stuck-at fault, well defined logic values are required both for fault activation as well as for fault effect propagation to observing outputs. In presence of X-values, classical test generation algorithms, based on topological algorithms or formal Boolean satisfiability (SAT) or BDD-based reasoning, may fail to generate testing patterns or to prove faults untestable. This work proposes the first efficient stuck-at fault ATPG algorithm able to prove testability or untestability of faults in presence of X-values. It overcomes the principal inaccuracy and pessimism of classical algorithms when X-values are considered. This accuracy is achieved by mapping the test generation problem to an instance of quantified Boolean formula (QBF) satisfiability. The resulting fault coverage improvement is shown by experimental results on ISCAS benchmark and larger industrial circuits.

Abstract

Runtime reconfigurable architectures based on Field-Programmable Gate Arrays (FPGAs) are attractive for realizing complex applications. However, being manufactured in latest semiconductor process technologies, FPGAs are increasingly prone to aging effects, which reduce the reliability of such systems and must be tackled by aging mitigation and application of fault tolerance techniques. This paper presents module diversification, a novel design method that creates different configurations for runtime reconfigurable modules. Our method provides fault tolerance by creating the minimal number of configurations such that for any faulty Configurable Logic Block (CLB) there is at least one configuration that does not use that CLB. Additionally, we determine the fraction of time that each configuration should be used to balance the stress and to mitigate the aging process in FPGA-based runtime reconfigurable systems. The generated configurations significantly improve reliability by fault-tolerance and aging mitigation.

Abstract

Increasing parameter variations, caused by variations in process, temperature, power supply, and wear-out, have emerged as one of the most important challenges in semiconductor manufacturing and test. As a consequence for gate delay testing, a single test vector pair is no longer sufficient to provide the required low test escape probabilities for a single delay fault. Recently proposed statistical test generation methods are therefore guided by a metric, which defines the probability of detecting a delay fault with a given test set. However, since run time and accuracy are dominated by the large number of required metric evaluations, more efficient approximation methods are mandatory for any practical application. In this work, a new statistical dynamic timing analysis algorithm is introduced to tackle this problem. The associated approximation error is very small and predominantly caused by the impact of delay variations on path sensitization and hazards. The experimental results show a large speedup compared to classical Monte Carlo simulations.

Abstract

The Resilience Articulation Point (RAP) model aims at provisioning researchers and developers with a probabilistic fault abstraction and error propagation framework covering all hardware/software layers of a System on Chip. RAP assumes that physically induced faults at the technology or CMOS device layer will eventually manifest themselves as a single or multiple bit flip(s). When probabilistic error functions for specific fault origins are known at the bit or signal level, knowledge about the unit of design and its environment allow the transformation of the bit-related error functions into characteristic higher layer representations, such as error functions for data words, Finite State Machine (FSM) state, macro interfaces or software variables. Thus, design concerns at higher abstraction layers can be investigated without the necessity to further consider the full details of lower levels of design. This paper introduces the ideas of RAP based on examples of radiation induced soft errors in SRAM cells and sequential CMOS logic. It shows by example how probabilistic bit flips are systematically abstracted and propagated towards higher abstraction levels up to the application software layer, and how RAP can be used to parameterize architecture level resilience methods.

Abstract

Computer simulations drive innovations in science and industry, and they are gaining more and more importance. However, their high computational demand generates extraordinary challenges for computing systems. Typical highperformance computing systems, which provide sufficient performance and high reliability, are extremly expensive. Modern GPUs offer high performance at very low costs, and they enable simulation applications on the desktop. However, they are increasingly prone to transient effects and other reliability threats. To fulfill the strict reliability requirements in scientific computing and simulation technology, appropriate fault tolerance measures have to be integrated into simulation applications for GPUs. Algorithm-Based Fault Tolerance on GPUs has the potential to meet these requirements. In this work we investigate the efficiency and the efficacy of ABFT for matrix operations on GPUs. We compare ABFT against fault tolerance schemes that are based on redundant computations and we evaluate its error detection capabilities

Abstract

Efficient access to on-chip instrumentation is a key enabler for post-silicon validation, debug, bringup or diagnosis. Re- configurable scan networks, as proposed by e.g. the IEEE Std. P1687, emerge as an effective and affordable means to cope with the increasing complexity of on-chip infrastructure. To access an element in a reconfigurable scan network, a scan- in bit sequence must be generated according to the current state and structure of the network. Due to sequential and combinational dependencies, the scan pattern generation process (pattern retargeting) poses a complex decision and optimization problem. This work presents a method for scan pattern generation with reduced access time. We map the access time reduction to a pseudo- Boolean optimization problem, which enables the use of efficient solvers to exhaustively explore the search space of valid scan-in sequences. This is the first automated method for efficient pattern retargeting in complex reconfigurable scan architectures such as P1687- based networks. It supports the concurrent access to multiple target scan registers (access merging) and generates reduced (short) scan-in sequences, considering all sequential and combinational dependencies. The proposed method achieves an access time reduction by up to 88x or 2.4x in average w.r.t. unoptimized satisfying solutions.

Abstract

This paper presents a novel method for synthesizing fault-secure circuits based on parity codes over groups of circuit outputs. The fault-secure circuit is able to detect all errors resulting from combinational and transition faults at a single node. The original circuit is not modified. If the original circuit is non-redundant, the result is a totally self-checking circuit. At first, the method creates the minimum number of parity groups such that the effect of each fault is not masked in at least one parity group. To ensure fault-secureness, the obtained groups are split such that no fault leads to silent data corruption. This is performed by a formal Boolean satisfiability (SAT) based analysis. Since the proposed method reduces the number of required parity groups, the number of two-rail checkers and the complexity of the prediction logic required for fault-secureness decreases as well. Experimental results show that the area overhead is much less compared to duplication and less in comparison to previous methods for synthesis of totally self-checking circuits. Since the original circuit is not modified, the method can be applied for fixed hard macros and IP cores.

Abstract

FPGA-based reconfigurable systems allow the online adaptation to dynamically changing runtime requirements. The reliability of FPGAs, being manufactured in latest technologies, is threatened by soft errors, as well as aging effects and latent defects.To ensure reliable reconfiguration, it is mandatory to guarantee the correct operation of the reconfigurable fabric. This can be achieved by periodic or on-demand online testing. This paper presents a reliable system architecture for runtime-reconfigurable systems, which integrates two non-concurrent online test strategies: Pre-configuration online tests (PRET) and post-configuration online tests (PORT). The PRET checks that the reconfigurable hardware is free of faults by periodic or on-demand tests. The PORT has two objectives: It tests reconfigured hardware units after reconfiguration to check that the configuration process completed correctly and it validates the expected functionality. During operation, PORT is used to periodically check the reconfigured hardware units for malfunctions in the programmable logic. Altogether, this paper presents PRET, PORT, and the system integration of such test schemes into a runtime-reconfigurable system, including the resource management and test scheduling. Experimental results show that the integration of online testing in reconfigurable systems incurs only minimum impact on performance while delivering high fault coverage and low test latency.

Abstract

The accessibility of on-chip embedded infrastructure for test, reconfiguration, and debug poses a serious safety and security problem. Special care is required in the design and development of scan architectures based on IEEE Std. 1149.1 (JTAG), IEEE Std. 1500, and especially reconfigurable scan networks, as allowed by the upcoming IEEE P1687 (IJTAG). Traditionally, the scan infrastructure is secured after manufacturing test using fuses that disable the test access port (TAP) completely or partially. The fuse-based approach is efficient if some scan chains or instructions of the TAP controller are to be permanently blocked. However, this approach becomes costly if fine-grained access management is required, and it faces scalability issues in reconfigurable scan networks. In this paper, we propose a scalable solution for multi-level access management in reconfigurable scan networks. The access to protected registers is restricted locally at TAP-level by a sequence filter which allows only a precomputed set of scan-in access sequences. Our approach does not require any modification of the scan architecture and causes no access time penalty. Experimental results for complex reconfigurable scan networks show that the area overhead depends primarily on the number of allowed accesses, and is marginal even if this number exceeds the count of network’s registers.

Abstract

Stringent reliability requirements call for monitoring mechanisms to account for circuit degradation throughout the complete system lifetime. In this work, we efficiently monitor the stress experienced by the system as a result of its current workload. To achieve this goal, we construct workload monitors that observe the most relevant subset of the circuit’s primary and pseudo-primary inputs and produce an accurate stress approximation. The proposed approach enables the timely adoption of suitable countermeasures to reduce or prevent any deviation from the intended circuit behavior. The relation between monitoring accuracy and hardware cost can be adjusted according to design requirements. Experimental results show the efficiency of the proposed approach for the prediction of stress induced by Negative Bias Temperature Instability (NBTI) in critical and near-critical paths of a digital circuit.

Abstract

Unknown (X) values in a circuit impair test quality and increase test costs. Classical n-valued algorithms for fault simulation and ATPG, which typically use a three- or four-valued logic for the good and faulty circuit, are in principle pessimistic in presence of X-values and cannot accurately compute the achievable fault coverage. In partial scan or pipelined circuits, X-values originate in non-scan flip-flops. These circuits are tested using multi-cycle tests. Here we present multi-cycle test generation techniques for circuits with X-values due to partial scan or other X-sources. The proposed techniques have been integrated into a multi-cycle ATPG framework which employs formal Boolean and quantified Boolean (QBF) satisfiability techniques to compute the possible signal states in the circuit accurately. Efficient encoding of the problem instance ensures reasonable runtimes. We show that in presence of X-values, the detection of stuck-at faults requires not only exact formal reasoning in a single cycle, but especially the consideration of multiple cycles for excitation of the fault site as well as propagation and controlled reconvergence of fault effects. For the first time, accurate deterministic ATPG for multi-cycle test application is supported for stuck-at faults. Experiments on ISCAS'89 and industrial circuits with X-sources show that this new approach increases the fault coverage considerably.

Abstract

FPGA-based reconfigurable systems allow the online adaptation to dynamically changing runtime requirements. However, the reliability of modern FPGAs is threatened by latent defects and aging effects. Hence, it is mandatory to ensure the reliable operation of the FPGA’s reconfigurable fabric. This can be achieved by periodic or on-demand online testing. In this paper, a system-integrated, transparent structural online test method for runtime reconfigurable systems is proposed. The required tests are scheduled like functional workloads, and thorough optimizations of the test overhead reduce the performance impact. The proposed scheme has been implemented on a reconfigurable system. The results demonstrate that thorough testing of the reconfigurable fabric can be achieved at negligible performance impact on the application.

Abstract

The precise estimation of dynamic power consumption, power droop and temperature development during scan test require a very large number of time–aware gate–level logic simulations. Until now, such characterizations have been feasible only for rather small designs or with reduced precision due to the high computational demands. We propose a new, throughput–optimized timing simulator on running on GPGPUs to accelerate these tasks by more than two orders of magnitude and thus providing for the first time precise and comprehensive toggle data for industrial–sized designs and over long scan test operations. Hazards and pulse–filtering are supported for the first time in a GPGPU accelerated simulator, and the system can easily be extended to even more sophisticated delay and power models.

Abstract

Apoptosis, the programmed cell death, is a physiological process that handles the removal of unwanted or damaged cells in living organisms. The process itself is initiated by signaling through tumor necrosis factor (TNF) receptors and ligands, which form clusters on the cell membrane. The exact function of this process is not yet fully understood and currently subject of basic research. Different mathematical models have been developed to describe and simulate the apoptotic receptor-clustering. In this interdisciplinary work, a previously introduced model of the apoptotic receptor-clustering has been extended by a new receptor type to allow a more precise description and simulation of the signaling process. Due to the high computational requirements of the model, an ef?cient algorithmic mapping to a modern many-core GPGPU architecture has been developed. Such architectures enable high-performance computing (HPC) simulation tasks on the desktop at low costs. The developed mapping reduces average simulation times from months to days (peak speedup of 256x), allowing the productive use of the model in research.

Abstract

Reconfigurable scan architectures allow flexible integration and efficient access to infrastructure in SoCs, e.g. for test, diagnosis, repair or debug. Such scan networks are often hierarchical and have complex structural and functional dependencies. For instance, the IEEE P1687 proposal, known as IJTAG, allows integration of multiplexed scan networks with arbitrary internal control signals. Common approaches for scan verification based on static structural analysis and functional simulation are not sufficient to ensure correct operation of these types of architectures. Hierarchy and flexibility may result in complex or even contradicting configuration requirements to access single elements. Sequential logic justification is therefore mandatory both to verify the validity of a scan network, and to generate the required access sequences. This work presents a formal method for verification of reconfigurable scan architectures, as well as pattern retargeting, i.e. generation of required scan-in data. The method is based on a formal model of structural and functional dependencies. Network verification and pattern retargeting is mapped to a Boolean satisfiability problem, which enables the use of efficient SAT solvers to exhaustively explore the search space of valid scan configurations.

Abstract

Efficient diagnosis procedures are crucial both for volume and for in-field diagnosis. In either case the underlying test strategy should provide a high coverage of realistic fault mechanisms and support a low-cost implementation. Built-in self-diagnosis (BISD) is a promising solution, if the diagnosis procedure is fully in line with the test flow. However, most known BISD schemes require multiple test runs or modifications of the standard scan-based test infrastructure. Some recent schemes circumvent these problems, but they focus on deterministic patterns to limit the storage requirements for diagnostic data. Thus, they cannot exploit the benefits of a mixed-mode test such as high coverage of non-target faults and reduced test data storage. This paper proposes a BISD scheme using mixed-mode patterns and partitioning the test sequence into “weak” and “strong” diagnostic windows, which are treated differently during diagnosis. As the experimental results show, this improves the coverage of non-target faults and enhances the diagnostic resolution compared to state-of-the-art approaches. At the same time the overall storage overhead for input and response data is considerably reduced.

Abstract

Pseudo-exhaustive test completely verifies all output functions of a combinational circuit, which provides a high coverage of non-target faults and allows an efficient on-chip implementation. To avoid long test times caused by large output cones, partial pseudo-exhaustive test (P-PET) has been proposed recently. Here only cones with a limited number of inputs are tested exhaustively, and the remaining faults are targeted with deterministic patterns. Using P-PET patterns for built-in diagnosis, however, is challenging because of the large amount of associated response data. This paper presents a built-in diagnosis scheme which only relies on sparsely distributed data in the response sequence, but still preserves the benefits of P-PET.

Abstract

Networks-on-Chip (NoCs) are implicitly fault tolerant and due to their inherent redundancy they can overcome defective cores, links and switches. This effect can be used to increase yield at the cost of reduced performance. In this paper, a new diagnosis method based on the standard flow of industrial volume testing is presented, which is able to identify the intact functions of a defective network switch rather than providing only a pass/fail result for the complete switch. To achieve this, the new method combines for the first time the precision of structural testing with information on the functional behavior in the presence of defects. This allows to disable defective parts of a switch after production test and use the intact functions. Thereby, only a minimum performance decrease is induced while the yield is increased. According to the experimental results, the method improves the performability of NoCs since 56.86 % and 72.42 % of defects in two typical switch models only impair one switch port. Unlike previous methods for implementing fault tolerant switches, the developed technique does not impose any additional area overhead and is compatible with many common switch designs.

Abstract

The automotive industry has to deal with an increasing amount of electronics in today’s vehicles. This paper describes the advantages of structural tests during in-field system test, reusing existing test data and on-chip structures. Demonstration is the embedded test of an ASIC within an automotive control unit, utilizing manufacturing scan-tests.

Abstract

Unknown or X-values during test application may originate from uncontrolled sequential cells or macros, from clock or A/D boundaries or from tri-state logic. The exact identification of X-value propagation paths in logic circuits is crucial in logic simulation and fault simulation. In the first case, it enables the proper assessment of expected responses and the effective and efficient handling of X-values during test response compaction. In the second case, it is important for a proper assessment of fault coverage of a given test set and consequently influences the efficiency of test pattern generation. The commonly employed n-valued logic simulation evaluates the propagation of X-values only pessimistically, i.e. the X-propagation paths found by n- valued logic simulation are a superset of the actual propagation paths. This paper presents an efficient method to overcome this pessimism and to determine accurately the set of signals which carry an X-value for an input pattern. As examples, it investigates the influence of this pessimism on the two applications X-masking and stuck-at fault coverage assessment. The experimental results on benchmark and industrial circuits assess the pessimism of classic algorithms and show that these algorithms significantly overestimate the signals with X-values. The experiments show that overmasking of test data during test compression can be reduced by an accurate analysis. In stuck-at fault simulation, the coverage of the test set is increased by the proposed algorithm without incurring any overhead.

Abstract

Markov-Chain Monte-Carlo (MCMC) methods are an important class of simulation techniques, which execute a sequence of simulation steps, where each new step depends on the previous ones. Due to this fundamental dependency, MCMC methods are inherently hard to parallelize on any architecture. The upcoming generations of hybrid CPU/GPGPU architectures with their multi-core CPUs and tightly coupled many-core GPGPUs provide new acceleration opportunities especially for MCMC methods, if the new degrees of freedom are exploited correctly. In this paper, the outcomes of an interdisciplinary collaboration are presented, which focused on the parallel mapping of a MCMC molecular simulation from thermodynamics to hybrid CPU/GPGPU computing systems. While the mapping is designed for upcoming hybrid architectures, the implementation of this approach on an NVIDIA Tesla system already leads to a substantial speedup of more than 87x despite the additional communication overheads.

Abstract

FPGA-based reconfigurable systems allow the online adaptation to dynamically changing runtime requirements. However, the reliability of FPGAs, which are manufactured in latest technologies, is threatened not only by soft errors, but also by aging effects and latent defects. To ensure reliable reconfiguration, it is mandatory to guarantee the correct operation of the underlying reconfigurable fabric. This can be achieved by periodic or on-demand online testing. The OTERA project develops and evaluates components and strategies for reconfigurable systems that feature reliable reconfiguration. The research focus ranges from structural online tests for the FPGA infrastructure and functional online tests for the configured functionality up to the resource management and test scheduling. This paper gives an overview of the project tasks and presents first results.

Abstract

Fault simulation is an essential tool in electronic design automation. The accuracy of the computation of fault coverage in classic n-valued simulation algorithms is compromised by unknown (X) values. This results in a pessimistic underestimation of the coverage, and overestimation of unknown (X) values at the primary and pseudo-primary outputs. This work proposes the first stuck-at fault simulation algorithm free of any simulation pessimism in presence of unknowns. The SAT-based algorithm exactly classifies any fault and distinguishes between definite and possible detects. The pessimism w. r. t. unknowns present in classic algorithms is discussed in the experimental results on ISCAS benchmark and industrial circuits. The applicability of our algorithm to large industrial circuits is demonstrated.

Abstract

Although CMOS technology scaling offers many advantages, it suffers from robustness problem caused by hard, soft and timing errors. The robustness of future CMOS technology nodes must be improved and the use of fault tolerant architectures is probably the most viable solution. In this context, Duplication/Comparison scheme is widely used for error detection. Traditionally, this scheme uses a static comparator structure that detects hard error. However, it is not effective for soft and timing errors detection due to the possible masking of glitches by the comparator itself. To solve this problem, we propose a pseudo-dynamic comparator architecture that combines a dynamic CMOS transition detector and a static comparator. Experimental results show that the proposed comparator detects not only hard errors but also small glitches related to soft and timing errors. Moreover, its dynamic characteristics allow reducing the power consumption while keeping an equivalent silicon area compared to a static comparator. This study is the first step towards a full fault tolerant approach targeting robustness improvement of CMOS logic circuits.

Abstract

An iterative flow to generate test sets providing high fault coverage under extreme parameter variations is presented. The generation is guided by the novel metric of circuit coverage, calculated by massively parallel statistical fault simulation on GPGPUs. Experiments show that the statistical fault coverage of the generated test sets exceeds by far that achieved by standard approaches.

Abstract

Non-functional properties (NFPs) of integrated circuits include reliability, vulnerability, power consumption or heat dissipation. Accurate NFP prediction over long periods of system operation poses a great challenge due to prohibitive simulation costs. For instance, in case of aging estimation, the existing low-level models are accurate but not efficient enough for simulation of complex designs. On the other hand, existing techniques for fast high-level simulation do not provide enough details for NFP analysis. The goal of this paper is to bridge this gap by combining the accuracy of low-level models with high-level simulation speed. We introduce an efficient mixed-level NFP prediction methodology that considers both the structure and application of a system. The system is modeled at transaction-level to enable high simulation speed. To maintain accuracy, NFP assessment for cores under analysis is conducted at gate-level by cycle-accurate simulation. We propose effective techniques for cross-level synchronization and idle simulation speed-up. As an example, we apply the technique to analyze aging caused by Negative Bias Temperature Instability in order to identify reliability hot spots. As case studies, several applications on an SoC platform are analyzed. Compared to conventional approaches, the proposed method is from 7 up to 400 times faster with mean error below 0.006%.

Abstract

Unknown (X) values, originating from memories, clock domain boundaries or A/D interfaces, may compromise test signatures and fault coverage. Classical logic and fault simulation algorithms are pessimistic w.r.t. the propagation of X values in the circuit. This work proposes efficient hybrid logic and stuck-at fault simulation algorithms which combine heuristics and local BDDs to increase simulation accuracy. Experimental results on benchmark and large industrial circuits show significantly increased fault coverage and low runtime. The achieved simulation precision is quantified for the first time.

Abstract

In this paper, a novel hybrid fault tolerant architecture for digital circuits is proposed in order to enable the use of future CMOS technology nodes. This architecture targets robustness, power consumption and yield at the same time, at area costs comparable to standard fault tolerance schemes. The architecture increases circuit robustness by tolerating both transient and permanent online faults. It consumes less power than the classical Triple Modular Redundancy (TMR) approach while utilizing comparable silicon area. It overcomes many permanent faults occurring throughout manufacturing while still tolerating soft errors introduced by particle strikes. These can be done by using scalable redundancy resources, while keeping the hardened combinational logic circuits intact. The technique combines different types of redundancy: information redundancy for error detection, temporal redundancy for soft error correction and hardware redundancy for hard error tolerance. Results on largest ISCAS and ITC benchmark circuits show that our approach has an area cost negligible of about 2% to 3% with a power consumption saving of about 30% compared to TMR. Finally, it deals with aging phenomenon and thus, increases the expected lifetime of logic circuits.

Abstract

Fault simulation of digital circuits must correctly compute fault coverage to assess test and product quality. In case of unknown values (X-values), fault simulation is pessimistic and underestimates actual fault coverage, resulting in increased test time and data volume, as well as higher overhead for design- for-test. This work proposes a novel algorithm to determine fault coverage with significantly increased accuracy, offering increased fault coverage at no cost, or the reduction of test costs for the targeted coverage. The algorithm is compared to related work and evaluated on benchmark and industrial circuits.

Abstract

Nanoelectronic circuits are increasingly affected by massive statistical process variations, leading to a paradigm shift in both design and test area. In circuit and system design, a broad class of methods for robustness like statistical design and self calibration has emerged and is increasingly used by the industry. The test community's answer to the massive-variation challenge is currently adaptive test. The test stimuli are modified on the fly (during test application) based on the circuit responses observed. The collected circuit outputs undergo statistical post-processing to facilitate pass/fail classification. We will present fundamentals of adaptive and robust test techniques and their theoretical background. While adaptive test is effective, the understanding how it covers defects under different process parameter combinations is not fully established yet with respect to algorithmic foundations. For this reason, novel analytic and algorithmic approaches in the field of variation-aware testing will also be presented in the tutorial. Coverage of defects in the process parameter space is modeled and maximized by an interplay between special fault simulation and multi-constrained ATPG algorithms. These systematic approaches can complement adaptive test application schemes to form a closed-loop system that combines analytical data with measurement results for maximal test quality.

Abstract

The paper presents an overview of a major research project on dependable embedded systems that has started in Fall 2010 and is running for a projected duration of six years. Aim is a 'dependability co-design' that spans various levels of abstraction in the design process of embedded systems starting from gate level through operating system, applications software to system architecture. In addition, we present a new classification on faults, errors, and failures.

Abstract

Die Mustererzeugung für den eingebetteten Test besteht häufig aus einer Phase zur Erzeugung von Zufallsmustern und einer Phase, in der deterministische Muster angelegt werden. Der vorliegende Beitrag stellt eine Methode vor, die erste Phase signifikant zu optimieren, um dadurch die Defekterfassung zu vergrößern und zugleich die Zahl der erforderlichen deterministischen Muster in der zweiten Phase zu reduzieren. Die Methode beruht auf dem pseudo-erschöpfenden Test (PET), der als Verfahren zum fehlermodellunabhängigen Test mit hoher Defekterfassung vorgeschlagen wurde. Da seine Testzeit exponentiell mit der Schaltungsgröße wachsen kann, ist die Anwendung auf große Schaltungen in der Regel ausgeschlossen. In der vorliegenden Arbeit werden eingebaute Testregister für den partiellen pseudo-erschöpfenden Test (P-PET) vorgeschlagen, der mit aktueller Technologie skaliert und hinsichtlich Testkosten und Testzeit mit dem üblichen pseudo-zufälligen Test (PZT) vergleichbar ist. Die Vorteile bezüglich der Defekterfassung, N-Detektierbarkeit für Haftfehler und der Reduktion deterministischer Testlängen werden anhand aktueller industrieller Schaltungen nachgewiesen.

Abstract

Robuste Schaltungen können bestimmte Fehler tolerieren, stellen aber auch besonders hohe Anforderungen an Test und Diagnose. Um Ausbeuteverluste zu vermeiden, muss der Test kritische Fehler von unkritischen Fehlern unterscheiden, die sich während des Systembetriebs nicht auswirken. Zur Verbesserung des Produktionsprozesses muss außerdem eine effiziente Diagnose für erkannte kritische Fehler unterstützt werden. Bisherige Arbeiten für Schaltungen mit Zeitredundanz haben gezeigt, dass ein Selbsttest mit Rücksetzpunkten kostengünstig kritische permanente Fehler von unkritischen transienten Fehlern unterscheiden kann. Hier wird der Selbsttest in N Sitzungen unterteilt, die bei einem Fehler sofort wiederholt werden. Tritt beim zweiten Durchlauf einer Sitzung kein Fehler mehr auf, geht man von einem transienten Fehler aus. Dabei genügt es, die Referenzantworten für die einzelnen Sitzungen in stark kompaktierter Form abzulegen. Statt einer vollständigen Signatur wird nur eine kurze Bitfolge gespeichert, welche die Signaturberechnung über mehrere Zeitpunkte hinweg charakterisiert. Die vorliegende Arbeit erweitert das Testen mit Rücksetzpunkten zu einem integrierten Test- und Diagnoseprozess. Es wird gezeigt, dass ein einziger Testdurchlauf mit stark kompaktierten Referenzwerten genügt, um eine vergleichbare diagnostische Auflösung zu erreichen wie bei einem Test ohne Antwortkompaktierung.

Abstract

Pattern generation for embedded testing often consists of a phase generating random patterns and a second phase where deterministic patterns are applied. This paper presents a method which optimizes the first phase significantly and increases the defect coverage, while reducing the number of deterministic patterns required in the second phase. The method is based on the concept of pseudo-exhaustive testing (PET), which was proposed as a method for fault model independent testing with high defect coverage. As its test length can grow exponentially with the circuit size, an application to larger circuits is usually impractical. In this paper, partial pseudo-exhaustive testing (P-PET) is presented as a synthesis technique for multiple polynomial feedback shift registers. It scales with actual technology and is comparable with the usual pseudo-random (PR) pattern testing regarding test costs and test application time. The advantages with respect to the defect coverage, N-detectability for stuck-at faults and the reduction of deterministic test lengths are shown using state-of-the art industrial circuits.

Abstract

In der vorliegenden Arbeit wird ein Schema zur Korrektur von transienten Fehlern in eingebetteten, pegelgesteuerten Speicherelementen vorgestellt. Das Schema verwendet Struktur- und Informationsredundanz, um Single Event Upsets (SEUs) in Registern zu erkennen und zu korrigieren. Mit geringem Mehraufwand kann ein betroffenes Bit lokalisiert und mit einem hier vorgestellten Bit-Flipping-Latch (BFL) rückgesetzt werden, so dass die Zahl zusätzlicher Taktzyklen im Fehlerfall minimiert wird. Ein Vergleich mit anderen Erkennungs- und Korrekturschemata zeigt einen deutlich reduzierten Hardwaremehraufwand. In this paper a soft error correction scheme for embedded level sensitive storage elements is presented. The scheme employs structural- and information-redundancy to detect and correct Single Event Upsets (SEUs) in registers. With low additional hardware overhead the affected bit can be localized and reset with the presented Bit-Flipping-Latch (BFL), thereby minimizing the amount of additional clock cycles in the faulty case. A comparison with other detection and correction schemes shows a significantly lower hardware overhead.

Abstract

In-field diagnosability of electronic components in larger systems such as automobiles becomes a necessity for both customers and system integrators. Traditionally, functional diagnosis is applied during integration and in workshops for infield failures or break-downs. However, functional diagnosis does not yield sufficient coverage to allow for short repair times and fast reaction on systematic failures in the production. Structural diagnosis could yield the desired coverage, yet recent builtin architectures which could be reused in the field either do not reveal diagnostic information or necessitate dedicated test schemes. The paper at hand closes this gap with a new built-in test method for autonomous in-field testing and in-field diagnostic data collection. The proposed Built-In Self-Diagnosis method (BISD) is based on the standard BIST architecture and can seamlessly be integrated with recent, commercial DfT techniques. Experiments with industrial designs show that its overhead is marginal and its structural diagnostic capabilities are comparable to those of external diagnosis on high-end test equipment.

Abstract

Robust circuits are able to tolerate certain faults, but also pose additional challenges for test and diagnosis. To improve yield, the test must distinguish between critical faults and such faults, that could be compensated during system operation; in addition, efficient diagnosis procedures are needed to support yield ramp-up in the case of critical faults. Previous work on circuits with time redundancy has shown that “signature rollback” can distinguish critical permanent faults from uncritical transient faults. The test is partitioned into shorter sessions, and a rollback is triggered immediately after a faulty session. If the repeated session shows the correct result, then a transient fault is assumed. The reference values for the sessions are represented in a very compact format. Storing only a few bits characterizing the MISR state over time can provide the same quality as storing the complete signature. In this work the signature rollback scheme is extended to an integrated test and diagnosis procedure. It is shown that a single test run with highly compacted reference data is sufficient to reach a comparable diagnostic resolution to that of a diagnostic session without any data compaction.

Abstract

Excessive power dissipation during VLSI testing results in over-testing, yield loss and heat damage of the device. For low power devices with advanced power management features and more stringent power budgets, power-aware testing is even more mandatory. Effective and efficient test set postprocessing techniques based on X-identification and power-aware X-filling have been proposed for external and embedded deterministic test. This work proposes a novel X-filling algorithm for combinational and broadcast-scan-based test compression schemes which have great practical significance. The algorithm ensures compressibility of test cubes using a SAT-based check. Compared to methods based on topological justification, the solution space of the compressed test vector is not pruned early during the search. Thus, this method allows much more precise low-power X-filling of test vectors. Experiments on benchmark and industrial circuits show the applicability to capture-power reduction during scan testing.

Abstract

In this paper a soft error correction scheme for embedded storage elements in level sensitive designs is presented. It employs space redundancy to detect and locate Single Event Upsets (SEUs). It is able to detect SEUs in registers and employ architectural replay to perform correction with low additional hardware overhead. Together with the proposed bit flipping latch an online correction can be implemented on bit level with a minimal loss of clock cycles. A comparison with other detection and correction schemes shows a significantly lower hardware overhead.

Abstract

As scaling of nanoelectronics may deteriorate dependability, fail-safe design techniques gain attention. We apply the concept of fail-safety to IP core-based system design, making the first step towards dependability-aware reuse methodologies. We introduce a methodology for dependability characterization, which uses informal techniques to identify hazards and employs formal methods to check if the hazards occur. The proposed hazard metrics provide qualitative and quantitative insight into possible core misbehavior. Experimental results on two IP cores show that the approach enables early comparative dependability studies.

Abstract

Moderne Diagnosealgorithmen können aus den vorhandenen Fehlerdaten direkt die defekte Schaltungsstruktur identifizieren, ohne sich auf spezialisierte Fehlermodelle zu beschränken. Solche Algorithmen benötigen jedoch Testmuster mit einer hohen Defekterfassung. Dies ist insbesondere im eingebetteten Test eine große Herausforderung. Der Partielle Pseudo-Erschöpfende Test (P-PET) ist eine Methode, um die Defekterfassung im Vergleich zu einem Zufallstest oder einem deterministischen Test für das Haftfehlermodell zu erhöhen. Wird die im eingebetteten Test übliche Phase der vorgeschalteten Erzeugung von Pseudozufallsmustern durch die Erzeugung partieller pseudo-erschöpfender Muster ersetzt, kann bei vergleichbarem Hardware-Aufwand und gleicher Testzeit eine optimale Defekterfassung für den größten Schaltungsteil erreicht werden. Diese Arbeit kombiniert zum ersten Mal P-PET mit einem fehlermodell-unabhängigen Diagnosealgorithmus und zeigt, dass sich beliebige Defekte im Mittel wesentlich präziser diagnostizieren lassen als mit Zufallsmustern oder einem deterministischen Test für Haftfehler. Modern diagnosis algorithms are able to identify the defective circuit structure directly from existing fail data without being limited to any specialized fault models. Such algorithms however require test patterns with a high defect coverage, posing a major challenge particularly for embedded testing. In mixed-mode embedded test, a large amount of pseudo-random patterns are applied prior to deterministic test pattern. Partial Pseudo-Exhaustive Testing (P-PET) replaces these pseudo-random patterns during embedded testing by partial pseudo-exhaustive patterns to test a large portion of a circuit fault-model independently. The overall defect coverage is optimized compared to random testing or deterministic tests using the stuck-at fault model while maintaining a comparable hardware overhead and the same test application time. This work for the first time combines P-PET with a fault model independent diagnosis algorithm and shows that arbitrary defects can be diagnosed on average much more precisely than with standard embedded testing. The results are compared to random pattern testing and deterministic testing targeting stuck-at faults.

Abstract

To achieve a high product quality for nano-scale systems, both realistic defect mechanisms and process variations must be taken into account. While existing approaches for variation-aware digital testing either restrict themselves to special classes of defects or assume given probability distributions to model variabilities, the proposed approach combines defect-oriented testing with statistical library characterization. It uses Monte Carlo simulations at electrical level to extract delay distributions of cells in the presence of defects and for the defect-free case. This allows distinguishing the effects of process variations on the cell delay from defectinduced cell delays under process variations. To provide a suitable interface for test algorithms at higher levels of abstraction, the distributions are represented as histograms and stored in a histogram data base (HDB). Thus, the computationally expensive defect analysis needs to be performed only once as a preprocessing step for library characterization, and statistical test algorithms do not require any low level information beyond the HDB. The generation of the HDB is demonstrated for primitive cells in 45 nm technology.

Abstract

In recent technology nodes, reliability is increasingly considered a part of the standard design flow to be taken into account at all levels of embedded systems design. While traditional fault simulation techniques based on low-level models at gate- and register transfer-level offer high accuracy, they are too inefficient to properly cope with the complexity of modern embedded systems. Moreover, they do not allow for early exploration of design alternatives when a detailed model of the whole system is not yet available, which is highly required to increase the efficiency and quality of the design flow. Multi-level models that combine the simulation efficiency of high abstraction models with the accuracy of low-level models are therefore essential to efficiently evaluate the impact of physical defects on the system. This paper proposes a methodology to efficiently implement concurrent multi-level fault simulation across gate- and transaction-level models in an integrated simulation environment. It leverages state-of-the-art techniques for efficient fault simulation of structural faults together with transaction-level modeling. This combination of different models allows to accurately evaluate the impact of faults on the entire hardware/software system while keeping the computational effort low. Moreover, since only selected portions of the system require low-level models, early exploration of different design alternatives is efficiently supported. Experimental results obtained from three case studies are presented to demonstrate the high accuracy of the proposed method when compared with a standard gate/RT mixed-level approach and the strong improvement of simulation time which is reduced by four orders of magnitude in average.

Abstract

Networks-on-Chip (NoCs) are implicitly fault tolerant due to their inherent redundancy. They can overcome defective cores, links and switches. As a side effect, yield is increased at the cost of reduced performability. In this paper, a new diagnosis method based on the standard flow of industrial volume testing is presented, which is able to identify the intact functions rather than providing only a pass/fail result for the complete switch. The new method combines for the first time the precision of structural testing with information on the functional behavior in the presence of defects to determine the unaffected switch functions and use partially defective NoC switches. According to the experimental results, this improves the performability of NoCs as more than 61% of defects only impair one switch port. Unlike previous methods for implementing fault tolerant switches, the developed technique does not impose any additional area overhead and is compatible with any switch design.

Abstract

Modern diagnosis algorithms are able to identify the defective circuit structure directly from existing fail data without being limited to any specialized fault models. Such algorithms however require test patterns with a high defect coverage, posing a major challenge particularly for embedded testing. In mixed-mode embedded test, a large amount of pseudorandom (PR) patterns are applied prior to deterministic test pattern. Partial Pseudo-Exhaustive Testing (P-PET) replaces these pseudo-random patterns during embedded testing by partial pseudo-exhaustive patterns to test a large portion of a circuit fault-model independently. The overall defect coverage is optimized compared to random testing or deterministic tests using the stuck-at fault model while maintaining a comparable hardware overhead and the same test application time. This work for the first time combines P-PET with a fault model independent diagnosis algorithm and shows that arbitrary defects can be diagnosed on average much more precisely than with standard embedded testing. The results are compared to random pattern testing and deterministic testing targeting stuck-at faults.

Abstract

In this paper we investigate the possibility of using commercial synthesis tools to build parity predictors for nano-electronic gates designs. They will be used as redundant resources for robustness improvement for future CMOS technology nodes.

Abstract

Modern many-core architectures with hundreds of cores provide a high computational potential. This makes them particularly interesting for scientific high-performance computing and simulation technology. Like all nano scaled semiconductor devices, many-core processors are prone to reliability harming factors like variations and soft errors. One way to improve the reliability of such systems is software-based hardware fault tolerance. Here, the software is able to detect and correct errors introduced by the hardware. In this work, we propose a software-based approach to improve the reliability of matrix operations on many-core processors. These operations are key components in many scientific applications.

Abstract

To cope with the numerous defect mechanisms in nanoelectronic technology, more and more complex fault models have been introduced. Each model comes with its own properties and algorithms for test generation and logic diagnosis. In diagnosis, however, the defect mechanisms of a failing device are not known in advance, and algorithms that assume a specific fault model may fail. Therefore, diagnosis techniques have been proposed that relax fault assumptions or even work without any fault model. In this chapter, we establish a generalized fault modeling technique and notation. Based on this notation, we describe and classify existing models and investigate the properties of a fault model independent diagnosis technique.

Abstract

In recent technology nodes, reliability is considered a part of the standard design flow at all levels of embedded system design. While techniques that use only low-level models at gate- and register transfer-level offer high accuracy, they are too inefficient to consider the overall application of the embedded system. Multi-level models with high abstraction are essential to efficiently evaluate the impact of physical defects on the system. This paper provides a methodology that leverages state-of-the-art techniques for efficient fault simulation of structural faults together with transaction-level modeling. This way it is possible to accurately evaluate the impact of the faults on the entire hardware/software system. A case study of a system consisting of hardware and software for image compression and data encryption is presented and the method is compared to a standard gate/RT mixed-level approach.

Abstract

Fault simulation is essential in test generation, design for test and reliability assessment of integrated circuits. Reliability analysis and the simulation of self-test structures are particularly computationally expensive as a large number of patterns has to be evaluated. In this work, we propose to map a fault simulation algorithm based on the parallel-pattern single-fault propagation (PPSFP) paradigm to many-core architectures and describe the involved algorithmic optimizations. Many-core architectures are characterized by a high number of simple execution units with small local memory. The proposed fault simulation algorithm exploits the parallelism of these architectures by use of parallel data structures. The algorithm is implemented for the NVIDIA GT200 Graphics Processing Unit (GPU) architecture and achieves a speed-up of up to 17x compared to an existing GPU fault-simulation algorithm and up to 16x compared to state-of-the-art algorithms on conventional processor architectures.

Abstract

Power consumption of circuits and systems receives more and more attention. In test mode, power consumption is even more critical than in system model and has severe impact on reliability, yield and test costs. This chapter describes the different types and sources of test power. Power-aware techniques for test pattern generation, design for test and test data compression are presented which allow efficient power constrained testing with minimized hardware cost and test application time.

Abstract

This paper provides a methodology that leverages state-of-the-art techniques for efficient fault simulation of structural faults together with transaction level modeling. This way it is possible to accurately evaluate the impact of the faults on the entire hardware/software system.

Abstract

This chapter describes Design-for-Test (DfT) techniques that allow for controlling the power consumption and reduce the overall energy consumed during a test. While some of the techniques described elsewhere in this book may also involve special DfT, the topics discussed here are orthogonal to those techniques and may be implemented independently.

Abstract

Moderne Many-Core-Architekturen bieten ein sehr hohes Potenzial an Rechenleistung. Dies macht sie besonders für Anwendungen aus dem Bereich des wissenschaftlichen Hochleistungsrechnens und der Simulationstechnik attraktiv. Die Architekturen folgen dabei einem Ausführungsparadigma, das sich am besten durch den Begriff “Many-Threading” beschreiben lässt. Wie alle nanoelektronischen Halbleiterschaltungen leiden auch Many-Core-Prozessoren potentiell unter störenden Einflüssen von transienten Fehlern (soft errors) und diversen Arten von Variationen. Diese Faktoren können die Zuverlässigkeit von Systemen negativ beeinflussen und erfordern Fehlertoleranz auf allen Ebenen, von der Hardware bis zur Software. Auf der Softwareseite stellt die Algorithmen-basierte Fehlertoleranz (ABFT) eine ausgereifte Technik zur Verbesserung der Zuverlässigkeit dar. Der Aufwand für die Anpassung dieser Technik an moderne Many-Threading-Architekturen darf jedoch keinesfalls unterschätzt werden. In diesem Beitrag wird eine effiziente und fehlertolerante Abbildung der Matrixmultiplikation auf eine moderne Many-Core-Architektur präsentiert. Die Fehlertoleranz ist dabei integraler Bestandteil der Abbildung und wird durch ein ABFT-Schema realisiert, das die Leistung nur unwesentlich beeinträchtigt. Modern many-core architectures provide a high computational potential, which makes them particularly interesting for applications from the fields of scientific high-performance computing and simulation technology. The execution paradigm of these architectures is best described as “Many-Threading”. Like all nano-scaled semiconductor devices, many-core processors are prone to transient errors (soft errors) and different kinds of variations that can have severe impact on the reliability of such systems. Therefore, fault-tolerance has to be incorporated at all levels, from the hardware up to the software. On the software side, Algorithm-based Fault Tolerance (ABFT) is a mature technique to improve the reliability. However, significant effort is required to adapt this technique to modern many-threading architectures. In this article, an efficient and fault-tolerant mapping of the matrix multiplication to a modern many-core architecture is presented. Fault-tolerance is thereby an integral part of the mapping and implemented through an ABFT scheme with marginal impact on the overall performance.

Abstract

Embedded testing, built-in self-test and methods for test compression rely on efficient test response compaction. Often, a circuit under test contains sources of unknown values (X), uninitialized memories for instance. These X values propagate through the circuit and may spoil the response signatures. The standard way to overcome this problem is X-masking. Outputs which carry an X value are usually determined by logic simulation. In this paper, we show that the amount of Xs is significantly overestimated, and in consequence outputs are overmasked, too. An efficient way for the exact computation of output Xs is presented for the first time. The resulting X-masking promises significant gains with respect to test time, test volume and fault coverage.

Abstract

In aktueller Prozesstechnologie muss die Zuverlässigkeit in allen Entwurfsschritten von eingebetteten Systemen betrachtet werden. Methoden, die nur Modelle auf unteren Abstraktionsebenen, wie Gatter- oder Registertransferebene, verwenden, bieten zwar eine hohe Genauigkeit, sind aber zu ineffizient, um komplexe Hardware/Software-Systeme zu analysieren. Hier werden ebenenübergreifende Verfahren benötigt, die auch hohe Abstraktion unterstützen, um effizient die Auswirkungen von Defekten im System bewerten zu können. Diese Arbeit stellt eine Methode vor, die aktuelle Techniken für die effiziente Simulation von strukturellen Fehlern mit Systemmodellierung auf Transaktionsebene kombiniert. Auf dieseWeise ist es möglich, eine präzise Bewertung der Fehlerauswirkung auf das gesamte Hardware/Software-System durchzuführen. Die Ergebnisse einer Fallstudie eines Hardware/Software-Systems zur Datenverschlüsselung und Bildkompression werden diskutiert und die Methode wird mit einem Standard-Fehlerinjektionsverfahren verglichen.

Abstract

High delay-fault coverage requires rather sophisticated clocking schemes in test mode, which usually combine launch-on-shift and launch-on-capture strategies. These complex clocking schemes make low power test planning more difficult as initialization, justification and propagation require multiple clock cycles. This paper describes a unified method to map the sequential test planning problem to a combinational circuit representation. The combinational representation is subject to known algorithms for efficient low power built-in self-test planning. Experimental results for a set of industrial circuits show that even rather complex test clocking schemes lead to an efficient low power test plan.

Abstract

Built-In Self-Test (BIST) is less often applied to random logic than to embedded memories due to the following reasons: Firstly, for a satisfiable fault coverage it may be necessary to apply additional deterministic patterns, which cause additional hardware costs. Secondly, the BIST-signature reveals only poor diagnostic information. Recently, the first issue has been addressed successfully. The paper at hand proposes a viable, effective and cost efficient solution for the second problem. The paper presents a new method for Built-In Self-Diagnosis (BISD). The core of the method is an extreme response compaction architecture, which for the first time enables an autonomous on-chip evaluation of test responses with negligible hardware overhead. The key advantage of this architecture is that all data, which is relevant for a subsequent diagnosis, is gathered during just one test session. The BISD method comprises a hardware scheme, a test pattern generation approach and a diagnosis algorithm. Experiments conducted with industrial designs substantiate that the additional hardware overhead introduced by the BISD method is on average about 15\% of the BIST area, and the same diagnostic resolution can be obtained as for external testing.

Abstract

Structural on-line self-test may be performed to detect permanent faults and avoid their accumulation in the system. This paper improves existing techniques for concurrent BIST that are based on a deterministic test set. Here, the test patterns are specially generated with a small number of specified bits. This results in very low test length and fault detection latency, which allows to frequently test critical faults. As a consequence, the likelihood of fault accumulation is reduced. Experiments with benchmark circuits show that the hardware overhead is significantly lower than the overhead of the state of the art. Moreover, a case-study on a super-scalar RISC processor demonstrates the feasibility of the method.

Abstract

In den letzten Jahrzehnten hat der Anteil der informationsverarbeitenden Komponenten an den Herstellungskosten mechatronischer Systeme rapide zugenommen. In den 70er Jahren machte die Informationsverarbeitung noch ca. 15% des Systems aus. Zu Beginn dieses Jahrtausends sind es bereits über 60% 8.9, wie auch aus Abb. 8.1 hervorgeht. Dieser Zuwachs in den Herstellungskosten ist auf die Zunahme der durch die Informationsverarbeitung realisierten Funktionen zurückzuführen. Sehr deutlich ist diese Zunahme im Automobil zu beobachten. Während das Antiblockiersystem und die digitale Motorsteuerung schon seit Jahren zum Standard gehören, werden nun zunehmend auch Fahrerassistenz- und Infotainmentsysteme ins Kraftfahrzeug integriert. Bei diesen Systemen beginnt die Grenze zwischen klassischer Sicherheits- und Komfortfunktion zu verschwimmen. Die Bandbreite möglichen Fehlverhaltens reicht vom Ausfall des Navigationssystems über Störungen der Zentralverriegelung bis hin zum automatischen Einleiten von Bremsmanövern bei hohen Geschwindigkeiten. Entsprechend ergeben sich hier hohe Anforderungen an die Zuverlässigkeit dieser Systeme.

Abstract

Dieser Artikel stellt eine Methode vor, den Entwurfsraum beim prüfgerechten Entwurf (engl. Design-for-Test, DfT) zu untersuchen und Teststrategien und Testschedules zu validieren. Alle Teile der Testinfrastruktur, wie etwa die Testeranbindung (Test Access Mechanisms), die Testwrapper, die Testdatenkompression sowie die entsprechenden Steuerwerke werden auf Transaktionsebenenmodelle (TLMs) abgebildet. Die kommunikationsbezogene Sicht der TLMs eignet sich besonders, da viele Aspekte des Tests die Übertragung großer Mengen an Teststimuli und -antworten erfordern. An einer Fallstudie wird der Einsatz von TLMs in frühen Entwurfsphasen erläutert. Der vorgestellte Ansatz hat wesentlich höhere Simulationseffizienz als Ansätze auf Register-Transfer- und Gatterebene.

Abstract

Programmable mixed-mode BIST schemes combine pseudo-random pattern testing and deterministic test. This paper presents a synthesis technique for a mixed-mode BIST scheme which is able to exploit the regularities of a deterministic test pattern set for minimizing the hardware overhead and memory requirements. The scheme saves more than 50\% hardware costs compared with the best schemes known so far while complete programmability is still preserved.

Abstract

Diagnosis is essential in modern chip production to increase yield, and debug constitutes a major part in the pre-silicon development process. For recent process technologies, defect mechanisms are increasingly complex, and continuous efforts are made to model these defects by using sophisticated fault models. Traditional static approaches for debug and diagnosis with a simplified fault model are more and more limited. In this paper, a method is presented, which identifies possible faulty regions in a combinational circuit, based on its input/output behavior and independent of a fault model. The new adaptive, statistical approach is named POINTER for 'Partially Overlapping Impact couNTER' and combines a flexible and powerful effect-cause pattern analysis algorithm with high-resolution ATPG. We show the effectiveness of the approach through experiments with benchmark and industrial circuits. In addition, even without additional patterns this analysis method provides good resolution for volume diagnosis, too.

Abstract

During volume testing, test application time, test data volume and high performance automatic test equipment (ATE) are the major cost factors. Embedded testing including built-in self-test (BIST) and multi-site testing are quite effective cost reduction techniques which may make diagnosis more complex. This paper presents a test response compaction scheme and a corresponding diagnosis algorithm which are especially suited for BIST and multi-site testing. The experimental results on industrial designs show, that test time and response data volume reduces significantly and the diagnostic resolution even improves with this scheme. A comparison with X-Compact shows, that simple parity information provides higher diagnostic resolution per response data bit than more complex signatures.

Abstract

Optimizing bandwidth by compression and compaction always has to solve the trade-off between input bandwidth reduction and output bandwidth reduction. Recently it has been shown that splitting scan chains into shorter segments and compacting the shift data outputs into a singleparity bit reduces the test response data to one bit per cycle without affecting fault coverage and diagnostic resolution if the compactor's structure is included into the ATPG process. This test data reduction at the output side comes with challenges at the input side. The bandwidth requirement grows due to the increased number of chains and due to a drastically decreased amount of don't care values in the test patterns. The paper at hand presents a new iterative approach to test set encoding which optimizes bandwidth on both input and output side while keeping the diagnostic resolution and fault coverage. Experiments with industrial designs demonstrate that test application time, test data volume and diagnostic resolution are improved at the same time and for most designs testing with a bandwidth of three bits per cycle is possible.

Abstract

Die Vorteile des Eingebauten Selbsttests (BIST --- Built-In Self-Test) sind bekannt, für eingebettete Speicher ist BIST sogar die bevorzugte Teststrategie. Für freie Logik wird BIST deutlich seltener eingesetzt. Grund hierfür ist zum einen, dass deterministische Testmuster für eine hohe Fehlerabdeckung benötigt werden und diese im Selbsttest hohe Kosten verursachen. Zum anderen lassen sich aus den Testantworten, die zu einer einzigen Signatur kompaktiert werden, nur wenige diagnostische Informationen ziehen. In den vergangenen Jahren wurden kontinuierlich Fortschritte zur Lösung des ersten Problems erzielt. Dieser Beitrag befasst sich mit der Lösung des zweiten Problems. Eine neue Methode für die Eingebaute Selbstdiagnose (BISD --- Built-In Self-Diagnosis) wird vorgeschlagen. Kern der Methode ist eine kombinierte, extreme Raum- und Zeitkompaktierung, die es erstmals ermöglicht, erwartete Antworten und fehlerhafte Antworten mit vernachlässigbarem Aufwand auf dem zu testenden Chip zu speichern. Somit können in einer einzigen Selbsttestsitzung pro Chip alle zur Diagnose notwendigen Daten gesammelt werden. Das BISD Schema umfasst neben der Kompaktierungshardware einen Diagnosealgorithmus und ein Verfahren zur Testmustererzeugung, die Aliasingeffekte und die durch die starke Kompaktierung verringerte diagnostische Auflösung kompensieren können. Experimente mit aktuellen, industriellen Schaltungen zeigen, dass die diagnostische Auflösung im Vergleich zum externen Test erhalten bleibt und der zusätzliche Hardware-Aufwand zu vernachlässigen ist. The advantages of Built-In Self-Test (BIST) are well known, and for embedded memories BIST is already the preferred test method. However, for random logic BIST is less often employed. This is mainly due to the following two reasons: On the one hand, deterministic patterns might be necessary to achieve reasonable fault coverage, yet they are expensive in built-in tests. On the other hand, the diagnostic information provided by BIST-signatures is rather poor. During the last years the first issue has been tackled successfully. This paper deals with the second issue. A new method for Built-In Self-Diagnosis (BISD) is presented. The method's backbone is a combination of extreme space and time compaction, which for the first time allows to store the expected test responses and the failing test responses with negligible overhead on chip. Consequently, all data relevant to diagnosis can be collected during a single self-test session. The BISD method additionally comprises a diagnosis algorithm and a test pattern generation scheme, which overcome aliasing and the reduced diagnostic resolution introduced by the extreme compaction. Experiments with recent, industrial designs demonstrate, that diagnostic resolution is maintaned compared to external testing and the additional hardware needed to implement the BISD-scheme is negligibly small.

Abstract

Im Hochvolumentest sind Testzeit, Testdatenvolumen und hochperformante Tester die entscheidenden Kostenfaktoren. Techniken des eingebetteten Tests wie ”Built–in Self–test“ (BIST) und ”Multi–site“–Testen senken effizient die Testkosten, machen die Diagnose aber schwerer. Diese Arbeit stellt ein Verfahren zur Antwortkompaktierung und ein entsprechendes Diagnoseverfahren vor, das sich besonders für BIST und den ”Multi–site“–Test eignet. Die experimentellen Ergebnisse an industriellen Schaltungen zeigen, dass sich mit diesem Ansatz gleichzeitig die Testzeit verk¨ urzt, das Antwortvolumen reduziert und die diagnostische Auflösung verbessert. Ein Vergleich mit X-Compact zeigt, dass einfache Paritäts–Informationen höhere diagnostische Auflösungen pro Antwortbit ermöglichen als komplexere Signaturen.

Abstract

Structural on-line self-test may be performed to detect permanent faults and avoid their accumulation. This paper improves concurrent BIST techniques based on a deterministic test set. Here, the test patterns are specially generated with a small number of specified bits. This results in very low test latency, which reduces the likelihood of fault accumulation. Experiments with a large number of circuits show that the hardware overhead is significantly lower than the overhead for previously published methods. Furthermore, the method allows to tradeoff fault coverage, test latency and hardware overhead.

Abstract

Für Speicherfelder sind fehlerkorrigierende Codes die vorherrschende Methode, um akzeptable Fehlerraten zu erreichen. In vielen aktuellen Schaltungen erreicht die Zahl der Speicherelemente in freier Logik die Größenordnung der Zahl von SRAM-Zellen vor wenigen Jahren. Zur Reduktion der Verlustleistung wird häufig der Takt der pegelgesteuerten Speicherelemente unterdrückt und die Speicherelemente müssen ihren Zustand über lange Zeitintervalle halten. Die Notwendigkeit Speicherzellen abzusichern wird zusätzlich durch die Miniaturisierung verstärkt, die zu einer erhöhten Empfindlichkeit der Speicherelemente geführt hat. Dieser Artikel stellt eine Methode zur fehlertoleranten Anordnung von pegelgesteuerten Speicherelementen vor, die bei unterdrücktem Takt Einfachfehler lokalisieren und Mehrfachfehler erkennen kann. Bei aktiviertem Takt können Einfach- und Mehrfachfehler erkannt werden. Die Register können ähnlich wie Prüfpfade effizient in den Entwurfsgang integriert werden. Die Diagnoseinformation kann auf Modulebene leicht berechnet und genutzt werden. For memories error correcting codes are the method of choice to guarantee acceptable error rates. In many current designs the number of storage elements in random logic reaches the number of SRAM-cells some years ago. Clock-gating is often employed to reduce the power dissipation of level-sensitive storage elements while the elements have to retain their state over long periods of time. The necessity to protect storage elements is amplified by the miniaturization, which leads to an increased susceptibility of the storage elements. This article proposes a method for the fault-tolerant arrangement of level-sensitive storage elements, which can locate single faults and detect multiple faults while being clock-gated. With active clock single and multiple faults can be detected. The registers can be efficiently integrated similar to the scan design flow. The diagnostic information can be easily computed and used at module level.

Abstract

This paper presents a technique that limits the maximum number of specified bits of any pattern in a given test set. The outlined method uses algorithms similar to ATPG, but exploits the information in the test set to quickly find test patterns with the desired properties. The resulting test sets show a significant reduction in the maximum number of specified bits in the test patterns. Furthermore, results for commercial ATPG test sets show that even the overall number of specified bits is reduced substantially

Abstract

Dealing with static and dynamic parameter variations has become a major challenge for design and test. To avoid unnecessary yield loss and to ensure reliable system operation a robust design has become mandatory. However, standard structural test procedures still address classical fault models and cannot deal with the non-deterministic behavior caused by parameter variations and other reasons. Chips may be rejected, even if the test reveals only non-critical failures that could be compensated during system operation. This paper introduces a scheme for embedded test, which can distinguish critical permanent and noncritical transient failures for circuits with time redundancy. To minimize both yield loss and the overall test time, the scheme relies on partitioning the test into shorter sessions. If a faulty signature is observed at the end of a session, a rollback is triggered, and this particular session is repeated. An analytical model for the expected overall test time provides guidelines to determine the optimal parameters of the scheme.

Abstract

Der während des Selbsttests von Schaltungen mit deaktivierbaren Prüfpfaden verwendete Testplan entscheidet über die Verlustleistung während des Tests. Bestehende Verfahren zur Erzeugung des Testplans verwenden überwiegend topologische Information, zum Beispiel den Ausgangskegel eines Fehlers. Aufgrund der implizit gegebenen Verknüpfung zwischen Testplan und Mustermenge ergeben sich weitreichende Synergieeffekte durch die Ausschöpfung mustermengenabhängiger Informationen. Die Verwendung von testmengenspezifischer Information im vorgestellten Algorithmus zeigt bei gleichbleibender Fehlererfassungsrate und Testdauer deutliche Einsparungen in der benötigten Verlustleistung. Das Verfahren wird an industriellen und Benchmark-Schaltungen mit bestehenden, überwiegend topologisch arbeitenden Verfahren verglichen.

Abstract

Zur Zuverlässigkeitsanalyse von Hardware-Software-Systemen ist ein Systemmodell notwendig, welches sowohl Struktur und Architektur der Hardware als auch die ausgeführte Funktion betrachtet. Wird einer dieser Aspekte des Gesamtsystems vernachlässigt, kann sich eine zu optimische oder zu konservative Schätzung der Zuverlässigkeit ergeben. Ein reines Strukturmodell der Hardware erlaubt, den Einfluss von logischer und struktureller Fehlermaskierung auf die Fehlerhäufigkeit der Hardware zu bestimmen. Allerdings kann ein solches Modell nicht die Fehlerhäufigkeit des Gesamtsystems hinreichend genau schätzen. Die Ausführung der Funktion auf dem System führt zu speziellen Nutzungs- und Kommunikationsmustern der Systemkomponenten, die zu erhöhter oder verminderter Anfälligkeit gegenüber Fehlern führen. Diese Arbeit motiviert die Modellierung funktionaler Aspekte zusammen mit der Struktur des Systems. Mittels Fehlerinjektion und Simulation wird der starke Einfluss der Funktion auf die Fehleranfälligkeit des Systems aufgezeigt. Die vorgestellte Methodik, funktionale Aspekte mit in die Zuverlässigkeitsmodellierung einzubinden, verspricht eine realistischere Bewertung von Hardware-Software-Systemen. Estimating the reliability of hardware-software systems allows to determine the robustness of design alternatives during design exploration. A system model used to derive such a reliability estimate has to incorporate the hardware structure and architecture of the system as well as the performed function. If merely the functional model or the structural model is considered separate from the other one, reliability estimation may be either too optimistic or too conservative. While an architectural model allows to determine the impact of logical and architectural fault masking on the design's error rate, it fails to correctly predict the failure rate of the overall system. The function that is performed by the design exhibits particular usage and communication patterns that may--depending on the function--result in increased or reduced susceptibility to faults. This work motivates to model functional aspects together with the architecture of the system. Fault injection and simulation show the strong influence of the function on the susceptability of the system. The proposed methodology to incorporate functional aspects into the system model for reliability estimation promises a more accurate assessment of hardware-software systems.

Abstract

An effective technique to save power during scan based test is to switch off unused scan chains. The results obtained with this method strongly depend on the mapping of scan flip-flops into scan chains, which determines how many chains can be deactivated per pattern. In this paper, a new method to cluster flip-flops into scan chains is presented, which minimizes the power consumption during test. The approach does not specify any ordering inside the chains and fits seamlessly to any standard tool for scan chain integration. The application of known test power reduction techniques to the optimized scan chain configurations shows significant improvements for large industrial circuits.

Abstract

In many modern circuits, the number of memory elements in the random logic is in the order of the number of SRAM cells on chips only a few years ago. In arrays, error correcting coding is the dominant technique to achieve acceptable soft-error rates. For low power applications, often latches are clock gated and have to retain their states during longer periods while miniaturization has led to elevated susceptibility and further increases the need for protection. This paper presents a fault-tolerant register latch organization that is able to detect single-bit errors while it is clock gated. With small addition, single and multiple errors are detected in the clocked mode, too. The registers can be efficiently integrated similar to the scan design flow, and error detecting or locating information can be collected at module level. The resulting structure can be efficiently reused for offline and general online testing.

Abstract

Keeping diagnostic resolution as high as possible while maximizing the compaction ratio is subject to research since the advent of embedded test. In this paper, we present a novel scan design methodology to maximize diagnostic resolution when compaction is employed. The essential idea is to consider the diagnostic resolution during the clustering of scan elements to scan chains. Our methodology does not depend on a fault model and is helpful with any type of compactor. A linear time heuristic is presented to solve the scan chain clustering problem. We evaluate our approach for industrial and academic benchmark circuits. It turns out to be superior to both random and to layout driven scan chain clustering. The methodology is applicable to any gate-level design and fits smoothly into an industrial design flow.

Abstract

Hardening a circuit against soft errors should be performed in early design steps before the circuit is laid out. A viable approach to achieve soft error rate (SER) reduction at a reasonable cost is to harden only parts of a circuit. When selecting which locations in the circuit to harden, priority should be given to critical spots for which an error is likely to cause a system malfunction. The criticality of the spots depends on parameters not all available in early design steps. We employ a selection strategy which takes only gate-level information into account and does not use any low-level electrical or timing information. We validate the quality of the solution using an accurate SER estimator based on the new UGC particle strike model. Although only partial information is utilized for hardening, the exact validation shows that the susceptibility of a circuit to soft errors is reduced significantly. The results of the hardening strategy presented are also superior to known purely topological strategies in terms of both hardware overhead and protection.

Abstract

Error correcting coding is the dominant technique to achieve acceptable soft-error rates in memory arrays. In many modern circuits, the number of memory elements in the random logic is in the order of the number of SRAM cells on chips only a few years ago. Often latches are clock gated and have to retain their states during longer periods. Moreover, miniaturization has led to elevated susceptibility of the memory elements and further increases the need for protection. This paper presents a fault-tolerant register latch organization that is able to detect single-bit errors while it is clock gated. With active clock, single and multiple errors are detected. The registers can be efficiently integrated similar to the scan design flow, and error detecting or locating information can be collected at module level. The resulting structure can be efficiently reused for offline and general online testing.

Abstract

This paper is an overview of the activities performed in the framework of the European IST project EuNICE-Test (European Network for Initial and Continuing Education in VLSI/SOC Testing) using remote automatic test equipment (ATE) ), addressing the shortage of skills in the microelectronics industry in the field of electronic testing. The project was based on the experience of the common test resource centre (CRTC) for French universities. In the framework of the EuNICE-Test project, the existing network expanded to 4 new academic centres: Universitat Politecnica de Catalunya, Spain, Politecnico di Torino, Italy, University of Stuttgart, Germany and Jozef Stefan Institute Ljubljana, Slovenia. Assessments of the results achieved are presented as well as course topics and possible future extensions.

Abstract

In this paper, we propose a new programmable deterministic Built-In Self-Test (BIST) method that requires significantly lower storage for deterministric patterns than existing programmable methods and provides high flexibilily for test engineering in bolh internal and external test. Theoretical analysis suggests that significanlly more care bits can be encoded in the seed or a Linear Feedback Shift Register (LFSR) if a limited number of conflicting equations are ignored in the employed linear equation system. The ignored care bits are separately embedded into the LFSR pattern, but in contrast to bit-flipping BIST, the test set is not embedded by a synthesized logic function. Instead, this information is stored in memory using a special compression architecture. Experiments for benchmark circuits industrial designs demonstrate that the approach has considerably higher overall coding efficency than the existing methods.

Abstract

Rising design complexity and shrinking structures pose new challenges for debug and diagnosis. Finding bugs and defects quickly during the whole life cycle of a product is crucial for time to market, time to volume and improved product quality. Debug of design errors and diagnosis of defects have many common aspects. In this paper we give an overview of state of the art algorithms, which tackle both tasks, and present an adaptive approach to design debug and logic diagnosis. Special design for diagnosis is needed to maintain visibility of internal states and diagnosability of deeply embedded cores. This article discusses current approaches to design for diagnosis to support all debug tasks from first silicon to the system level.

Abstract

In this paper, we propose a new programmable deterministic Built-In Self-Test (BIST) method that requires significantly lower storage for deterministic patterns than existing programmable methods and provides high flexibility for test engineering in both internal and external test. Theoretical analysis suggests that significantly more care bits can be encoded in the seed of a Linear Feedback Shift Register (LFSR), if a limited number of conflicting equations is ignored in the employed linear equation system. The ignored care bits are separately embedded into the LFSR pattern. In contrast to known deterministic BIST schemes based on test set embedding, the embedding logic function is not hardwired. Instead, this information is stored in memory using a special compression and decompression method. Experiments for benchmark circuits and industrial designs demonstrate that the approach has considerably higher overall coding efficiency than the existing methods.

Abstract

Many STUMPS architectures found in current chip designs allow disabling of individual scan chains for debug and diagnosis. In a recent paper it has been shown that this feature can be used for reducing the power consumption during test. Here, we present an efficient algorithm for the automated generation of a test plan that keeps fault coverage as well as test time, while significantly reducing the amount of wasted energy. A fault isolation table, which is usually used for diagnosis and debug, is employed to accurately determine scan chains that can be disabled. The algorithm was successfully applied to large industrial circuits and identifies a very large amount of excess pattern shift activity.

Abstract

Die stark erhöhte durchschnittliche und maximale Verlustleistung während des Tests integrierter Schaltungen kann zu einer Beeinträchtigung der Ausbeute bei der Produktion sowie der Zuverlässigkeit im späteren Betrieb führen. Wir stellen eine Testplanung für Schaltungen mit parallelen Prüfpfaden vor, welche die Verlustleistung während des Tests reduziert. Die Testplanung wird auf ein überdeckungsproblem abgebildet, das mit einem heuristischen Lösungsverfahren effizient auch für große Schaltungen gelöst werden kann. Die Effizienz des vorgestellten Verfahrens wird sowohl für die bekannten Benchmarkschaltungen als auch für große industrielle Schaltungen demonstriert.

Abstract

Diagnosis is essential in modern chip production to increase yield, and debug constitutes a major part in the presilicon development process. For recent process technologies, defect mechanisms are increasingly complex, and continuous efforts are made to model these defects by using sophisticated fault models. Traditional static approaches for debug and diagnosis with a simplified fault model are more and more limited. In this paper, a method is presented, which identifies possible faulty regions in a combinational circiut, based on its input/output behavior and independent of a fault model. The new adaptive, statistical approach combines a flexible and powerful effect-cause pattern analysis algorithm with high-resolution ATPG. We show the effectiveness of the approach through experiments with benchmark and industrial circuits.

Abstract

A special logic synthesis problem is considered for Boolean functions which have large don't care sets and are irregular. Here, a function ist considered as irregular if the input assignments mapped to specified values ('1'or'0') are randomly spread over the definition space. Such functions can be encounted in the field of design for test. The proposed method uses ordered BDDs for logic manipulations and generates freeBDD-like covers. For the considered benchmark functions, implementations were found with the significant reduction of the node/gate count as compared to SIS or the methodes offered by a state-of-the-art BDD package.

Abstract

Decreasing feature sizes have led to an increased vulnerability of random logic to soft errors. In combinational logic a particle strike may lead to a glitch at the output of a gate, also referred to as single even transient (SET), which in turn can propagate to a register and cause a single event upset (SEU) there. Circuit level modeling and analysis of SETs provides an attractive compromise between computationally expensive simulations at device level and less accurate techniques at higher levels. At the circuit level particle strikes crossing a pn-junction are traditionally modeled with the help of a transient current source. However, the common models assume a constant voltage across the pn-junction, which may lead to inaccurate predictions concerning the shape of expected glitches. To overcome this problem, a refined circuit level model for strikes through pnjunctions is investigated and validated in this paper. The refined model yields significantly different results than common models. This has a considerable impact on SEU prediction, which is confirmed by extensive simulations at gate level. In most cases, the refined, more realistic, model reveals an almost doubled risk of a system failure after an SET.

Abstract

Neben der zunehmenden Anfälligkeit gegenüber Fertigungsfehlern bereiten insbesondere vermehrte Parameterschwankungen, zeitabhängige Materialveränderungen und eine erhöhte Störanfälligkeit während des Betriebs massive Probleme bei der Qualitätssicherung für nanoelektronische Systeme. Für eine wirtschaftliche Produktion und einen zuverlässigen Systembetrieb wird einerseits ein robuster Entwurf unabdingbar, andererseits ist damit auch ein Paradigmenwechsel beim Test erforderlich. Anstatt lediglich defektbehaftete Systeme zu erkennen und auszusortieren, muss der Test bestimmen, ob ein System trotz einer gewissen Menge von Fehlern funktionsfähig ist, und die verbleibende Robustheit gegenüber Störungen im Betrieb charakterisieren. Im Rahmen des Projekts RealTest werden einheitliche Entwurfs- und Teststrategien entwickelt, die sowohl einen robusten Entwurf als auch eine darauf abgestimmte Qualitätssicherung unterstützen.

Abstract

The increased number of fabrication defects, spatial and temporal variability of parameters, as well as the growing impact of soft errors in nanoelectronic systems require a paradigm shift in design, verification and test. A robust design becomes mandatory to ensure dependable systems and acceptable yields. Design robustness, however, invalidates many traditional approaches for testing and implies enormous challenges. The RealTest Project addresses these problems for nanoscale CMOS and targets unified design and test strategies to support both a robust design and a coordinated quality assurance after manufacturing and during the lifetime of a system. The paper first gives a short overview of the research activities within the project and then focuses on a first result concerning soft errors in combinational logic. It will be shown that common electrical models for particle strikes in random logic have underestimated the effects on the system behavior. The refined model developed within the RealTest Project predicts about twice as many single events upsets (SEUs) caused by particle strikes as traditional models.

Abstract

An efficient on-chip infrastructure for memory test and repair is crucial to enhance yield and availability of SoCs. A commonly used repair strategy is to equip memories with spare rows and columns (2D redundancy). To advoid the prohibitive storage requirements for failure bitmaps and the complex data structures inherent in most algorithms for offline repair analysis, existing heuristics for built-in repair analysis (BIRA) either use very simple search strategies or restict the search to smaller local bitmaps. Exact BIRA algorithms work with sub analyzers for each possible repair combination. While a parallel implementation suffers from a high hardware overhead, a serial implementation leads to increased test times. Recently an integrated built-in test and repair approach has been proposed which interleaves test and repair analysis and supports an exact solution with moderate hardware overhead and reasonable test times. The search is based on a depth first traversal of a binary tree, which can be efficiently implemented using a stack of limited size. This algorithm can be realized with different repair strategies guiding the selection of spare rows or columns in each step. In this paper the impact of four different repair strategies on the test and repair time is analyzed.

Abstract

Rising design complexity and shrinking structures pose new challenges for debug and diagnosis. Finding bugs and defects quickly during the whole life cycle of a product is crucial for time to market, time to volume and improved product quality. Debug of design errors and diagnosis of defects have many common aspects. In this paper we give an overview of state of the art algorithms, which tackle both tasks, and present an adaptive approach to design debug and logic diagnosis. Special design for diagnosis is needed to maintain visibility of internal states and diagnosability of deeply embedded cores. This article discusses current approaches to design for diagnosis to support all debug tasks from first silicon to the system level.

Abstract

BIST is an attractive approach to detect delay faults due to its inherent support for at-speed test. Deterministic logic BIST (DLBIST) is a technique which was successfully applied to stuck-at fault testing. As delay faults have lower random pattern testability than stuck-at faults, the need for DLBIST schemes is increased. Nevertheless, an extension to delay fault testing is not trivial, since this necessitates the application of pattern pairs. Consequently, delay fault testing is expected to require a larger mapping effort and logic overhead than stuck-at fault testing. In this paper, we consider the so-called transition fault model, which is widely used for complexity reasons. We present an extension of a DLBIST scheme for transition fault testing. Functional justification has been used to generate the required pattern pairs. The efficiency of the extended scheme is investigated by using difficult to test industrial designs.

Abstract

An efficient on-chip infrastructure for memory test and repair is crucial to enhance yield and availability of SoCs. A commonly used repair strategy is to equip memories with spare rows and columns (2D redundancy). Although exact algorithms are available for offline repair analysis, they cannot be directly applied on-chip because of the prohibitive storage requirements for failture bitmaps and the complex data structures inherent in the algorithms. Existing heuristics for built-in repair analysis (BIRA) try to circumvent this problem either by very simple search strategies or by restricting the search to smaller local bitmaps. Exact BIRA algorithms work with sub analyzers for each possible repair combination. While a parallel implementation suffers from a high hardware overhead, a serial implementation leads to high test times. The integrated built-in test and repair approach proposed in this paper interleaves test and repair analysis and supports an exact solution without failure bitmap. The search can be implemented with a stack, which is limited by the number of redundant elements. The basic search procedure is combined with an efficient technique to continuously reduce the problem complexity and keep the test and analysis time low.

Abstract

The increased number of fabrication defects, spatial and temporal variability of parameters, as well as the growing impact of soft errors in nanoelectronic systems require a paradigm shift in design, verification and test. A robust design becomes mandatory to ensure dependable systems and acceptable yields. Design robustness, however, invalidates many traditional approaches for testing and implies enormous challenges. The RealTest Project addresses these problems for nanoscale CMOS and targets unified design and test strategies to support both a robust design and a coordinated quality assurance after manufacturing and during the lifetime of a system. The paper first gives a short overview of the research activities within the project and then focuses on a first result concerning soft errors in combinational logic. It will be shown that common electrical models for particle strikes in random logic have underestimated the effects on the system behavior. The refined model developed within the RealTest Project predicts about twice as many single events upsets (SEUs) caused by particle strikes as traditional models.

Abstract

Aufgrund der unvollständigen Informationen über ein mechatronisches System stellt die Frühe Zuverlässigkeitsbewertung eine große Herausforderung dar. Um die jeweiligen Vorteile zu nutzen, wurden klassische Ansätze in den einzelnen Domänen kombiniert und in eine ganzheitliche Methode zur Zuverlässigkeitsbewertung in den Frühen Entwicklungsphasen integriert. In Zusammenarbeit verschiedener Ingenieursdisziplinen wurde die ganzheitliche Methode um die rechnergestützte Ermittlung von Fehlerzusammenhängen im Rahmen einer Risikoabschätzung und verschiedene qualitative Modellierungs- und Analyseansätze erweitert. für die systematische Analyse des wechselseitigen Einflusses der beteiligten Domänen und die Integration in die Zuverlässigkeitsbewertung wurden Wechselwirkungen zwischen den Domänen untersucht und klassifiziert.

Abstract

Entwurf, Verifikation und Test zuverlässiger nanoelektronischer Systeme erfordern grundlegend neue Methoden und Ansätze. Ein robuster Entwurf wird unabdingbar, um Fertigungsfehler, Parameterschwankungen, zeitabhängige Materialveränderungen und vorübergehende Störungen in gewissem Umfang zu tolerieren. Gleichzeitig verlieren gerade dadurch viele traditionelle Testverfahren ihre Aussagekraft. Im Rahmen des Projekts RealTest werden einheitliche Entwurfs- und Teststrategien entwickelt, die sowohl einen robusten Entwurf als auch eine darauf abgestimmte Qualitätssicherung unterstützen. The increasing number of fabrication defects, spatial and temporal variability of parameters, as well as the growing impact of soft errors in nanoelectronic systems require a paradigm shift in design, verification and test. A robust design is mandatory to ensure dependable systems and acceptable yields. The quest for design robustness, however, invalidates many traditional approaches for testing and implies enormous challenges. Within the framework of the RealTest project unified design and test strategies are developed to support a robust design and a coordinated quality assurance after the production and during the lifetime of a system.

Abstract

Built-in self test is a major part of the manufacturing test procedure for the Cell Processor. However, pseudo random patterns cause a high switching activity which is not effectively reduced by dynamic clock gating. Therefore, the test power envelope is expected to be so high, that the scan-speed has to be reduced significantly, thus extending test time. We propose a test power reduction method that uses scan-gating with Logic BIST. In LBIST, except for the first dozens of patterns, patterns that detect additional faults (effective patterns) are very scarce and often less than one pattern in a hundred detects new faults. In most cases, such an effective pattern even requires only a reduced set of the available scan chains to detect the fault and all don't-care scan chains can be disabled, therefore significantly reducing test power.

Abstract

Scan architectures, though widely used in modern designs, are expensive in power consumption. In this paper, we discuss the issues of excessive peak power consumption during scan testing. We show that taking care of high current levels during the test cycle (i.e. between launch and capture) is highly relevant to avoid noise phenomena such as IR-drop or ground bounce. We propose a solution based on power-aware assignment of don´t care bits in deterministic test patterns. For ISCAS´89 and ITC´99 benchmark circuits, this approach reduces peak power during the test cycle up to 89\% compared to a random filling solution.

Abstract

Design, Verification and Test of integrated circuits with millions of gates put strong requirements on design time, test volume, test application time, test speed and diagnostic resolution. In this paper, an overview is given on the common aspects of these tasks and how they interact. Diagnosis techniques may be used after manufacturing, for chip characterization and field return analysis, and even for rapid prototyping.

Abstract

Built-in self test is a major part of the manufacturing test procedure for the Cell Processor. However, pseudo random patterns cause a high switching activity which is not effectively reduced by standard low power design techniques. If special care is not taken, the scan-speed may have to be reduced significantly, thus extending test time and costs. In this paper, we describe a test power reduction method for logic BIST which uses test scheduling, planning and scan-gating. In LBIST, effective patterns that detect additional faults are very scarce after a few dozens of scan cycles and often less than one pattern in a hundred detects new faults. In most cases, such an effective pattern requires only a reduced set of the available scan chains to detect the fault and all don´t-care scan chains can be disabled, therefore significantly reducing test power.

Abstract

We present a technique for making a circuit ready for logic built-in self test by masking unknown values at its outputs. In order to keep the silicon area costs low, some known bits in output responses are also allowed to me masked. These bits are selected based on a stuck-at n-detection based metric, such that the impact of masking on the defect coverage is minimal. An analysis based on a probabilistic model for resistive short defects indicates that the coverage loss for unmodeled defects is negligible for relatively low values of n.

Abstract

Software-based self-test (SBST) of processors offers many benefits, such as dispense with expensive test equipments, test execution during maintenance and in the field or initialization tests for the whole system. In this paper, for the first time a structural SBST methodology is proposed which optimizes energy, average power consumption, test length and fault coverage at the same time.

Abstract

BIST is an attractive approach to detect delay faults due to its inherent support for at-speed test. Deterministic logic BIST (DLBIST) is a technique which was successfully applied to stuck-at fault testing. As delay faults have lower random pattern testability than stuck-at faults, the need for DLBIST schemes is increased. Nevertheless, an extension to delay fault testing is not trivial, since this necessitates the application of pattern pairs. Consequently, delay fault testing is expected to require a larger mapping effort and logic overhead than stuck-at fault testing. In this paper, we consider the so-called transition fault model, which is widely used for complexity reasons. We present an extension of a DLBIST scheme for transition fault testing. Functional justification is used to generate the required pattern pairs. The efficiency of the extended scheme is investigated by using industrial benchmark circuits.

Abstract

Scan architectures, though widely used in modern designs for testing purpose, are expensive in power consumption. In this paper, we first discuss the issues of excessive peak power consumption during scan testing. We next show that taking care of high current levels during the test cycle (i.e. between launch and capture) is highly relevant so as to avoid noise phenomena such as irdrop or ground bounce. Then, we propose a solution based on power-aware assignment of don´t care bits in deterministic test patterns that considers structural information of the circuit under test. Experiments have been performed on ISCAS´89 and ITC´99 benchmark circuits with the proposed structural-based power-aware X-Filling technique. These results show that the proposed technique provides the best tradeoff between peak power reduction and increase of test sequence length.

Abstract

Der softwarebasierende Selbsttest von Prozessoren (SBST) bietet zahlreiche Vorteile wie den Verzicht auf teure Testautomaten, die autonome Testdurchführung während der Wartung oder die Möglichkeit, einen Initialisierungstest für das Gesamtsystem zu implementieren. In dieser Arbeit wird eine strukturbasierte SBST Methode vorgestellt, die bezüglich Energieaufnahme, durchschnittlicher Verlustleistung, Testlänge und Fehlerüberdeckung gleichzeitig optimiert.

Abstract

A method for test resource partitioning is introduced which keeps the design-for-test logic test set independent and moves the test pattern dependent information to an external, programmable chip. The scheme includes a new decompression scheme for a fast and efficient communication between the external test chip and the circuit under test. The hardware costs on chip are significantly lower compared with a deterministic BIST scheme while the test application time is still in the same range. The proposed scheme is fully programmable, flexible and can be reused at board level for testing in the field. Keywords: Deterministic self-test, external BIST, test resource partitioning, test data compression.

Abstract

Open source software are becoming more widely-used, notably in the server and desktop applications. For embedded systems development, usage of open source software can also reduce development and licensing costs. We report on our experience in developing a Systemon- a-Chip (SoC) audio player using various open source components in both hardware and software parts as well as in the development process. The Ogg Vorbis audio decoder targeted for limited computing resource and low power consumption devices was developed on the free LEON SoC platform, which features SPARC-V8 architecture compatible processor and AMBA bus. The decoder runs on the open source RTEMS operating system making use of the royalty-free open source Vorbis library. We also aim to illustrate the use of hardware/software co-design techniques. Therefore, in order to speed up the decoding process, after an analysis, a computing-intensive part of the decoding algorithm was selected and designed as an AMBA compatible hardware core. The demonstration prototype was built on the XESS XSV-800 prototyping board using GNU/Linux workstations as development workstations. This project shows that development of SoC using open source platform is viable and might be the preferred choice in the future.

Abstract

Mechatronische Systeme sind heutzutage allgegenwärtig. Durch die Kombination aus Mechanik und moderner Informationsverarbeitung (Elektronik und Software) kann die Leistungsfähigkeit von Produkten deutlich gesteigert werden. Ein Beispiel hierfür sind CVTGetriebe. Die ersten Getriebe dieser Bauart waren weitgehend mechanisch/hydraulische Strukturen 1. Modernere CVT-Getriebe, wie das ZF Ecotronic 2 oder das Front-CVT der Mercedes-Benz A-Klasse 3 verfügen über eine elektronische Steuerung, die die Leistungsfähigkeit des Getriebes zu steigern vermag aber auch zu UnZuverlässigkeiten führen kann. In diesem Beitrag soll das Thema der Zuverlässigkeit mechatronischer Systeme aufgegriffen werden und insbesondere vor dem Hintergrund der Zuverlässigkeitsarbeit in Frühen Entwicklungsphasen diskutiert werden, da namentlich die Konzeptphase durch die Auswahl des richtigen Konzeptes für den endgültigen Produkterfolg hauptverantwortlich ist. Hierzu wird speziell das Thema der Informationsgewinnung in Frühen Phasen thematisiert, da der Erfolg der Zuverlässigkeitsarbeit maßgeblich von der Daten- und Informationslage abhängig ist.

Abstract

For the first time, we study the coverage of non-target defects for Deterministic Logic BIST (DLBIST) architecture. We consider several DLBIST implementation options that result in test sequences of different lengths. Resistive bridging faults are used as a surrogate of non-target defects. Experimental data obtained for largest ISCAS benchmarks suggests that, although DLBIST always guarantees complete stuck-at coverage, test sequence length does influence the non-target defect detection capabilities. For circuits with a large fraction of random-pattern resistant faults, the embedded deterministic patterns as well as a sufficient amount of random patterns are both demonstrated to be essential for non-target defect detection. It turns out, moreover, that area cost is lower for DLBIST solutions with longer test sequences, due to additional degrees of freedom for the embedding procedure and a lower number of faults undetected by pseudorandom patterns. This implies that DLBIST is particularly effective in covering non-target defects.

Abstract

Testing integrated circuits with millions of transistors puts strong requirements on test volume, test application time, test speed, and test resolution. To overcome these challenges, it is widely accepted to partition test resources between the automatic test equipment (ATE) and the circuit under test (CUT). These strategies may reach from simple test data compression/decompression schemes to implementing a complete built-in self-test. Very often these schemes come with reduced diagnostic resolution. In this paper, an overview is given on techniques for embedding test into a circuit while still keeping diagnostic capabilities. Built-in diagnosis techniques may be used after manufacturing, for chip characterization and field return analysis, and even for rapid prototyping.