Vector restoration using accelerated validation and refinement

Given a test sequence and a list of faults detected by the sequence, vector restoration techniques extract a minimal subsequence that detects a chosen subset of faults. Vector restoration techniques are useful in static compaction of test sequences and in fault diagnosis. We propose a new vector restoration technique that is a significant improvement over the state of the art in several ways: (1) a sequence of length n can be restored with only O(nlog2n) simulations while known approaches require simulation of O(n²) vectors; (2) a two-step restoration process is used that makes vector restoration practical for large designs; and (3) the restoration process for several faults is overlapped to provide significant acceleration in vector restoration. Our new ideas can be used to improve run-times of known static compaction and fault diagnosis methods. We integrated the proposed vector restoration technique into a static test sequence compaction system. Our experiments show that the new restoration technique, as compared to known techniques, is for (1) about 2 times faster for the ISCAS benchmark circuits, and for (2) 3 to 5 times faster on large, industrial designs. Using the new restoration technique, we successfully processed large industrial designs that could not be handled by earlier techniques in 2 CPU days