Improving a nonenumerative method to estimate path delay fault coverage

A recently proposed method obtains path delay fault coverages by estimating the count of the number of tested faults instead of actually enumerating them. The estimate becomes pessimistic when several paths share a set of lines. In this communication, we present a continuum of improved approximations for the counting method, approaching exact fault simulation, to allow tradeoffs between accuracy and complexity. Higher accuracy is obtained at the expense of CPU time. We propose the use of flags 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 length of segments is increased, the accuracy becomes close to that of the exact fault simulation, even with small segment lengths.