Exact stuck-at fault classification in presence of unknowns

Fault simulation is an essential tool in electronic design automation. The accuracy of the computation of fault coverage in classic n-valued simulation algorithms is compromised by unknown (X) values. This results in a pessimistic underestimation of the coverage, and overestimation of unknown (X) values at the primary and pseudo-primary outputs. This work proposes the first stuck-at fault simulation algorithm free of any simulation pessimism in presence of unknowns. The SAT-based algorithm exactly classifies any fault and distinguishes between definite and possible detects. The pessimism w.r.t. unknowns present in classic algorithms is discussed in the experimental results on ISCAS benchmark and industrial circuits. The applicability of our algorithm to large industrial circuits is demonstrated.