IMPROVING A NONENUMERATIVE METHOD TO ESTIMATE PATH DELAY-FAULT COVERAGE

A recently proposed method obtains path delay fault coverages by estim ating the count of the number of tested faults instead of actually enu merating them. The estimate becomes pessimistic when several paths sha re a set of lines. In this communication, we present a continuum of im proved approximations for the counting method, approaching exact fault simulation, to allow tradeoffs between accuracy and complexity. Highe r accuracy is obtained at the expense of CPU time. We propose the use of Bags corresponding to fixed-length path segments. A flag indicates whether or not the segment has been included in a previously detected path fault. A path fault, detected by a pair of vectors, is counted as a new detection only if it includes at least one segment not included in any previously tested path fault. The results show that as the len gth of segments is increased, the accuracy becomes close to that of th e exact fault simulation, even with small segment lengths.