Synthesizing safe state machines from Esterel

Abstract

Esterel and Safe State Machines (SSMs) are synchronous languages dedicated to the modeling of embedded reactive systems. While Esterel is a textual language, SSMs are based on the graphical Statecharts formalism. Statecharts are often more intuitive to understand than their textual counterpart, and their animated simulation can help to visualize subtle behaviors of a program. However, in terms of editing speed, revision management, and meta-modeling, the textual nature of Esterel is advantageous. We present an approach to transform Esterel v5 programs into equivalent SSMs. This permits a design flow where the designer develops a system at the Esterel level, but uses a graphical browser and simulator to inspect and validate the system under development.We synthesize SSMs in two phases. The first phase transforms an Esterel program into an equivalent SSM, using a structural translation that results in correct, but typically not very compact SSMs. The second phase iteratively applies optimization rules that aim to reduce the number of states, transitions and hierarchy levels to enhance readability of the SSM. As it turned out, this optimization is also useful for the traditional, manual design of SSMs. The complete transformation has been implemented in a prototypical modeling environment, which allows to demonstrate the practicality of this approach and the compactness of the generated SSMs.