Cycle-based symbolic simulation of gate-level synchronous circuits

Abstract

Symbolic methods are often considered the state-of-the-art technique for validating digital circuits. Due to their complexity and unpredictable run-time behavior, however, their potential is currently limited to small-to-medium circuits. Logic simulation privileges capacity, it is nicely scalable, flexible, and it has a predictable run-time behavior. For this reason, it is the common choice for validating large circuits. Simulation, however, typically visits only a small fraction of the state space. The discovery of bugs heavily relies on the expertise of the designer of the test stimuli. In this paper we consider a symbolic simulation approach to the validation problem. Our objective is to trade-off between formal and numerical methods in order to simulate a circuit with a large number of input combinations and sequences in parallel. We demonstrate larger capacity with respect to symbolic techniques and better efficiency with respect to cycle-based simulation. We show that it is possible to symbolically simulate very large trace sets in parallel (over 100 symbolic inputs) for the largest ISCAS benchmark circuits, using 96 Mbytes of memory.