Detecting State Coding Conflicts in STG Unfoldings Using SAT

The behaviour of asynchronous circuits is often described by Signal Transition Graphs (STGs), which are Petri nets whose transitions are interpreted as rising and falling edges of signals. One of the crucial problems in the synthesis of such circuits is that of identifying whether an STG satisfies the Complete State Coding (CSC) requirement, e.g., by using model checking based on the state graph of an STG. In this paper, we avoid constructing the state graph of an STG, which can lead to state space explosion, and instead use only the information about causality and structural conflicts between the events involved in a finite and complete prefix of its unfolding. The algorithm is derived by adopting the Boolean Satisfiability (SAT) approach. This technique leads not only to huge memory savings when compared to methods based on state graphs, but also to significant speedups. Keywords: asynchronous circuits, automated synthesis, complete state coding, CSC, Petri nets, signal transition graphs, STG, SAT, net unfoldings.