Deviation-Based LFSR Reseeding for Test-Data Compression

Abstract

Abstract-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.

¹K.S. Neelukumari and ²Dr. K.B. Jayanthi

“…Since the amount of compression for LFSR reseeding depends on the number of specified bits, the proposed approach exploits this property. In Wang et al (2008) and Chandra and Chakrabarty (2000) output deviation method is used to select the effective test pattern from large n-detect set. The confidence level of each gate is used to check the output for various input combination.…”