We describe a hybrid formal hardware verification tool that links the HOL interactive proof system and the MDG automated hardware verification tool. It supports a hierarchical verification approach that mirrors the hierarchical structure of designs. We obtain advantages of both verification paradigms. We illustrate its use by considering a component of a communications chip. Verification with the hybrid tool is significantly faster and more tractable than using either tool alone.

There exist a wide range of hardware verification tools, some based on interactive theorem proving and other more automated tools based on decision diagrams. In this paper, we compare three different verification systems covering the spectrum of today's verification technology. In particular, we consider HOL, MDG and VIS. HOL is an interactive theorem proving system based on higher-order logic. VIS is an automatic system based on ROBDDs and integrating verification with simulation and synthesis. The MDG system is an intermediate approach based on Multiway Decision Graphs providing automation while accommodating abstract data sorts, uninterpreted functions and rewriting. As the basis for our comparison we used all three systems to independently model and verify a fabricated ATM communications chip: the Fairisle 4 4 switch fabric.