Natalia Lylina

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.

Zusammenfassung

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.