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Linear feedback shift register (LFSR) reseeding forms the basis for many test-compression solutions. A seed can be computed for each test cube by solving a system of linear equations based on the feedback polynomial of the LFSR. Despite the availability of numerous LFSR-reseeding-based compression methods in the literature, relatively little is known about the effectiveness of these seeds for unmodeled defects, particularly since there are often several candidate seeds for a test cube. We use the recently proposed output deviation measure of the resulting patterns as a metric to select appropriate LFSR seeds. Experimental results are reported using test patterns for stuck-at and transition faults derived from selected seeds for the ISCAS-89 and the IWLS-05 benchmark circuits. These patterns achieve higher coverage for transition and stuck-open faults than patterns obtained using other seed-generation methods for LFSR reseeding. Given a pattern pair (p 1, p 2) for transition faults, we also examine the transition-fault coverage for launch on capture by using p 1 and p 2 to separately compute output deviations. Results show that p 1 tends to be better when there is a high proportion of do-not-care bits in the test cubes, while p 2 is a more appropriate choice when the transition-fault coverage is high.
Computer-Aided Design of Integrated Circuits and Systems, IEEE Transactions on (Volume:28 , Issue: 2 )
Date of Publication: Feb. 2009