A polynomial time flow for implementing free-choice Petri-nets

Abstract

FSM and PTnet control models are pertinent in both software and hardware applications as both specification and implementation models. The state-based, monolithic FSM model is directly implementable in software or hardware, but cannot model concurrency without state explosion. Interacting FSM models have so far lacked the formal rigor for expressing the synchronising interactions between different FSMs. The event-based, PTnet model is able to model both concurrency and choice within the same model, however lacks a polynomial time flow to implementation, as current methods of exposing the event state space require a potentially exponential number of states. In this work, we present a polynomial complexity flow for transforming a Free-Choice PTnet into a new formalism for Interacting FSMs, i.e Multiple, Synchronised FSMs (MSFSMs), a compact Interacting FSMs model, potentially implementable using any existing monolithic FSM implementation method. We believe that such a flow can in the long term bridge the event and state-based models. We present execution time and state space results of exercising our flow on 25 large PTnet specifications, describing asynchronous control circuits, and contrast our results to the popular Petrify tool for PTnet state space exploration and circuit implementation. Our results indicate a very significant reduction in both state space size and execution time.