Section: New Results

Extensions of the language and the model

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

The different works on using the polychronous model as semantic median model (which has also a syntactic instance) for different effective models (AADL, Simulink via GeneAuto, UML via CCSL...) lead us to study various possible extensions of the semantic model as well as the syntactic one. Some of them have already been defined while for others, the study is still ongoing. In particular, we plan to add to the Signal language a new syntax for automata, partly inspired from AADL mode automata and hierarchic automata existing in other formalisms. An automaton is considered as an instance of a new process model and the “and” composition is the Signal composition.

A fundamental issue that we wish to address in a new way is that of globally asynchronous, locally synchronous (GALS), or globally asynchronous, locally polychronous systems. The idea we have is to extend Signal with a syntactic structure that encapsulates a polychronous (or synchronous) process $P$ in a system, $S$, that creates a continuous temporal domain providing a real-time clock presented in different time units (..., fs, ..., ms, ..., sec, mn, ...). Such a real-time clock can be used as a usual “synchronous” signal in the process $P$ encapsulated in $S$. Systems $S_1$, ..., $S_n$ may be composed (with the standard composition of Signal) in a same system $S$, but the ms of a given system $S_i$ is a priori not synchronous with the ms of another system $S_j$. Then it is possible to specify standard Signal constraints in the system $S$ on these different signals, to express for instance some variation limits of different clocks.

We have also started a new work on causality aspects in order to express and operate more elaborate dependencies than instantaneous dependencies currently computed on the graph of a program. This theoretical work allows one to express dependencies that cross several instants, in a formal framework of word automata and graph algebra.