A Novel $ {\rm x}$-ploiting Strategy for Improving Performance of Test Data Compression

A precomputed core test set contains a large number of don't cares (
x
's) that can be effectively exploited to improve test data compression (TDC). Extending pattern run-length coding, we present a novel strategy that propagates the
x
's of a reference pattern to a new reference pattern in such a way that the reference pattern is xor-ed with the pattern to be encoded. The
x
-propagating strategy can increase the probability of a reference pattern being coding-compatible with the pattern to be encoded, and its validity can be established by filling some
x
's of the already encoded patterns in backtracing way. How our strategy is used for TDC is demonstrated. Experimental results for large ISCAS89 benchmarks show that, compared to the recently proposed schemes, our technique can effectively improve compression and simplify on-chip decoder, and work better when used for core-unified TDC.