Executing Safe State Machines on a Reactive Processor

Safe State Machines (SSMs) are a Statechart dialect with precise synchronous semantics, used to describe the behavior of reactive systems. A natural target for executing SSMs are reactive processors, which have an instruction set architecture (ISA) particularly well-suited for reactive control flow. When synthesizing SSMs into code, this is traditionally done via the synchronous language Esterel. However, this is not always straightforward; transitions in SSMs can jump arbitrarily between states, and there is no Esterel statement that matches this. We here propose to circumvent this by synthesizing SSMs directly onto a reactive ISA that can encode transitions directly as GOTOs. This not only has the potential for smaller and faster code, but preserves the structure of the SSM much better that going via Esterel. Conversely, we note that SSMs appear easier to implement on a reactive processor than Esterel, notably because there is not exception handling required.