On The Verification of Sequential Machines at Differing Levels of Abstraction

In this paper, an algorithm is presented for the verification of the equivalence of two sequential circuit descriptions at the same or differing levels of abstraction, namely at the register-transfer (RT) level and the logic level. The descriptions represent general finite automata at the differing levels -- a finite automaton can be described in a ISP-like language and its equivalence to a logic level implementation can be verified using our algorithm. Two logic level automatons can be similarly verified for equivalence. Previous approaches to sequential circuit verification have been restricted to verifying relatively simple descriptions with small amounts of memory. Unlike these approaches, our technique is shown to be computationally efficient for much more complex circuits. The efficiency of our algorithm lies in the exploitation of don't care information derivable from the RTL or logic level description (e.g invalid input and output sequences) during the verification process. Using efficient cube enumeration procedures at the logic level we have been able to verify the equivalence of finite automata with a large number of states in small amounts of cpu-time.