VERISEC: verifying equivalence of sequential circuits using SAT

In this paper we propose a framework to verify equivalence of sequential circuits using Boolean satisfiability (SAT). We tackle a problem that is harder than the traditional sequential hardware equivalence; specifically, we address the uninvestigated problem of verifying delay replaceability as stated in V. Singhal et al. (2001) of two sequential designs. This notion of sequential equivalence does not make any assumptions either about the design-environment or about the design's steady state behavior. Thus, verifying delay replaceability is considered as hard as verifying safe replaceability according to V. Singhal et al. (2001) of sequential circuits (conjectured as EXPSPACE complete). Our SAT-based framework has the following salient features: (a) a methodology to inductively prove equivalence (delay replaceability) of sequential circuits with no assumptions about any initial state; (b) a scheme to include sequential logic implications into the framework; and (c) a low-cost scheme to identify equivalent flip-flop pairs on the fly. We used our tool to successfully verify several sequential benchmark circuits. Low execution times make our framework practical and scalable.