skip to main content

Title: Covering Undetected Transition Fault Sites with Optimistic Unspecified Transition Faults under Multicycle Tests
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.
Authors:
Award ID(s):
1714147
Publication Date:
NSF-PAR ID:
10061924
Journal Name:
European Test Symposium
Sponsoring Org:
National Science Foundation
More Like this
  1. 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,more »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.« less
  2. 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.
  3. 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 involvemore »bridging faults demonstrate the importance of eliminating diagnostic holes.« less
  4. A recent work showed that it is possible to transform a single-cycle test for stuck-at faults into a launch-on-shift (LOS) test that is guaranteed to detect the same stuck-at faults without any logic or fault simulation. The LOS test also detects transition faults. This was used for obtaining a compact LOS test set that detects both types of faults. In the scenario where LOS tests are used for both stuck-at and transition faults, this article observes that, under certain conditions, the detection of a stuck-at fault guarantees the detection of a corresponding transition fault. This implies that the two faults are equivalent under LOS tests. Equivalence can be used for reducing the set of target faults for test generation and test compaction. The article develops this notion of equivalence under LOS tests with equal primary input vectors and provides an efficient procedure for identifying it. It presents experimental results to demonstrate that such equivalences exist in benchmark circuits, and shows an unexpected effect on a test compaction procedure.
  5. Graphics Processing Units (GPUs) have rapidly evolved to enable energy-efficient data-parallel computing for a broad range of scientific areas. While GPUs achieve exascale performance at a stringent power budget, they are also susceptible to soft errors, often caused by high-energy particle strikes, that can significantly affect the application output quality. Understanding the resilience of general purpose GPU applications is the purpose of this study. To this end, it is imperative to explore the range of application output by injecting faults at all the potential fault sites. This problem is especially challenging because unlike CPU applications, which are mostly single-threaded, GPGPU applications can contain hundreds to thousands of threads, resulting in a tremendously large fault site space - in the order of billions even for some simple applications. In this paper, we present a systematic way to progressively prune the fault site space aiming to dramatically reduce the number of fault injections such that assessment for GPGPU application error resilience can be practical. The key insight behind our proposed methodology stems from the fact that GPGPU applications spawn a lot of threads, however, many of them execute the same set of instructions. Therefore, several fault sites are redundant and can bemore »pruned by a careful analysis of faults across threads and instructions. We identify important features across a set of 10 applications (16 kernels) from Rodinia and Polybench suites and conclude that threads can be first classified based on the number of the dynamic instructions they execute. We achieve significant fault site reduction by analyzing only a small subset of threads that are representative of the dynamic instruction behavior (and therefore error resilience behavior) of the GPGPU applications. Further pruning is achieved by identifying and analyzing: a) the dynamic instruction commonalities (and differences) across code blocks within this representative set of threads, b) a subset of loop iterations within the representative threads, and c) a subset of destination register bit positions. The above steps result in a tremendous reduction of fault sites by up to seven orders of magnitude. Yet, this reduced fault site space accurately captures the error resilience profile of GPGPU applications.« less