Section: New Results

Code generation for poly-endochronous processes

Participants : Loïc Besnard, Thierry Gautier, Jean-Pierre Talpin.

The synchronous modeling paradigm provides strong correctness guarantees for embedded system design while requiring minimal environmental assumptions. In most related frameworks, global execution correctness is achieved by ensuring the insensitivity of (logical) time in the program from (real) time in the environment. Tis property, called endochrony, can be statically checked, making it fast to ensure design correctness. Unfortunately, it is not preserved by composition, which makes it difficult to exploit with component-based design concepts in mind. It has been shown that compositionality can be achieved by weakening the objective of endochrony: a weakly endochronous system is a deterministic system that can perform independent computations and communications in any order as long as this does not alter its global state. Moreover, the non-blocking composition of weakly endochronous processes is isochronous, which means that the synchronous and asynchronous compositions of weakly endochronous processes accept the same behaviors. Unfortunately, testing weak endochrony needs state-space exploration, which is very costly in the general case. Then, a particular case of weak endochrony, called polyendochrony, was defined, which allows static checking thanks to the existing clock calculus. The clock hierarchy of a polyendochronous system may have several trees, with synchronization relations between clocks placed in different trees, but the clock expressions of the clock system must be such that there is no clock expression (especially, no root clock expression) defined by symmetric difference: root clocks cannot refer to absence. In other words, the clock system must be in disjunctive form [10].

We have now implemented code generation for poly-endochronous systems in Polychrony. This generation reuses techniques of distributed code generation, with rendez-vous management for synchronization constraints on clocks which are not placed in the same tree of clocks. The approach has been validated on several use cases running in parallel with time to time synchronization.