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1. Target Faults for Test Compaction Based on Multicycle Tests

   https://doi.org/10.1145/3375278  

   Pomeranz, Irith (March 2020, ACM Transactions on Design Automation of Electronic Systems)

   null (Ed.)

   The use of multicycle tests, with several functional capture cycles between scan operations, contributes significantly to the ability to compact a test set. Multicycle tests have the added benefit that they can contribute to the detection of defects with complex behaviors that are not detected by single-cycle or two-cycle tests. To ensure that this benefit is materialized when test compaction is applied to transition faults, this article suggests to incorporate into the test compaction procedure an additional fault model whose fault coverage increases when multicycle tests are used. To ensure that the computational complexity of test compaction is not increased by a fault model with a large number of faults, or faults with complex behaviors, the added fault model is required to have the same characteristics as the transition fault model. A type of transition fault called unspecified transition fault satisfies these requirements. The article describes a test compaction procedure for transition faults that incorporates unspecified transition faults, and presents experimental results for benchmark circuits to demonstrate the levels of test compaction and fault coverage that can be achieved. 

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2. Diagnostic Test Generation that Addresses Diagnostic Holes

   Pomeranz, I (January 2018, IEEE transactions on computer-aided design of integrated circuits and systems)

   A diagnostic test generation procedure targets fault pairs in a set of target faults with the goal of distinguishing all the fault pairs. When a fault pair cannot be distinguished, it prevents the diagnostic test set from providing information about the faults, and consequently, about defects whose diagnosis would have benefited from a diagnostic test for the indistinguishable fault pair. This is referred to in this paper as a diagnostic hole. The paper observes that it is possible to address diagnostic holes by targeting different but related fault pairs, possibly from a different fault model. As an example, the paper considers the case where diagnostic test generation is carried out for single stuck-at faults, and related bridging faults are used for addressing diagnostic holes. Considering fault detection, an undetectable single stuck-at fault implies that certain related bridging faults are undetectable. The paper observes that, even if a pair of single stuck-at faults is indistinguishable, a related pair of bridging faults may be distinguishable. Based on this observation, diagnostic tests for pairs of bridging faults are added to a diagnostic test set when the related single stuck-at faults are indistinguishable. Experimental results of defect diagnosis for defects that do not involve bridging faults demonstrate the importance of eliminating diagnostic holes. 

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3. TURTLE: A Low-Cost Fault Injection Platform for SRAM-based FPGAs

   https://doi.org/10.1109/ReConFig48160.2019.8994782  

   Thurlow, Corbin; Rowberry, Hayden; Wirthlin, Michael (December 2019, 2019 International Conference on ReConFigurable Computing and FPGAs (ReConFig))

   This paper presents the TURTLE fault injection platform for inserting faults into SRAM FPGAs. The TURTLE system is designed to gather significant fault injection data to test and validate radiation-induced single-event upset (SEU) mitigation techniques for FPGAs. The TURTLE is a low-cost fault injection platform that emulates upsets within the configuration memory (CRAM) of an FPGA through partial reconfiguration. This work successfully implemented the proposed architecture and performed several successful fault injection campaigns on multiple designs and SEU mitigation techniques. Results in this paper show large amounts of data collected from a fault injection campaign used to validate the PCMF SEU mitigation technique. Over 170 million injections were performed using the TURTLE for this campaign. 

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4. Covering Undetected Transition Fault Sites with Optimistic Unspecified Transition Faults under Multicycle Tests

   Pomeranz, I (May 2018, European Test Symposium)

   When a transition fault test set leaves undetected transition faults because of logic redundancies, test constraints, or the existence of hard-to-detect faults, it leaves transition fault sites uncovered. For the case where multicycle tests are used, this paper explores the possibility of covering the sites of undetected transition faults by using tests for what are referred to as optimistic unspecified transition faults. For this discussion, a standard transition fault is associated with an extra delay of a single clock cycle. An unspecified transition fault captures in a single fault the behaviors of transition faults of different durations. Because faults with different durations may be detectable or undetectable independently by a multicycle test, an unspecified transition fault may be detected even if the standard transition fault at the same site is undetectable. This effect is enhanced with optimistic unspecified transition faults. The paper describes an iterative test compaction procedure for multicycle tests that supplements the set of standard transition faults with optimistic unspecified transition faults to cover the sites of undetected standard transition faults. 

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5. Covering Test Holes of Functional Broadside Tests

   https://doi.org/10.1145/3441282  

   Pomeranz, Irith (February 2021, ACM Transactions on Design Automation of Electronic Systems)

   null (Ed.)

   Functional broadside tests were developed to avoid overtesting of delay faults. The tests achieve this goal by creating functional operation conditions during their functional capture cycles. To increase the achievable fault coverage, close-to-functional scan-based tests are allowed to deviate from functional operation conditions. This article suggests that a more comprehensive functional broadside test set can be obtained by replacing target faults that cannot be detected with faults that have similar (but not identical) detection conditions. A more comprehensive functional broadside test set has the advantage that it still maintains functional operation conditions. It covers the test holes created when target faults cannot be detected by detecting similar faults. The article considers the case where the target faults are transition faults. When a standard transition fault, with an extra delay of a single clock cycle, cannot be detected, an unspecified transition fault is used instead. An unspecified transition fault captures the behaviors of transition faults with different extra delays. When this fault cannot be detected, a stuck-at fault is used instead. A stuck-at fault has some of the detection conditions of a transition fault. Multicycle functional broadside tests are used to allow unspecified transition faults to be detected. As a by-product, test compaction also occurs. The structure of the test generation procedure accommodates the complexity of producing functional broadside tests by considering the target as well as replacement faults together. Experimental results for benchmark circuits demonstrate the fault coverage improvements achieved, and the effect on the number of tests. 

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