Practical considerations in formal equivalence checking of PowerPC microprocessors

Recently, formal verification has become more a part of the VLSI design methodology. Formally verifying a design guarantees 100% coverage and negates the need to do simulation. Theoretically, 100% coverage is very appealing and formal verification looks to be the panacea to solve the coverage problem. However, there are many practical considerations in deploying formal verification in real design environments. These considerations if not evaluated can lead to ineffective and even erroneous formal verification methodologies. In this paper we show how to make formal verification a successful part of a design methodology by paying attention to practical considerations and knowing the limitations of formal verification. We show the errors that can result by making over generalized assumptions and how they can be avoided. We do this in the context of the design of PowerPC microprocessors. We limit ourselves to a formal verification technique commonly used in our design methodology-boolean equivalence checking.