Julien Ouy

From multi-clocked synchronous processes to latency-insensitive modules

We consider the problem of synthesizing correct-by-construction globally asynchronous, locally synchronous (GALS) implementations from modular synchronous specifications. This involves the synthesis of asynchronous wrappers that drive the synchronous clocks of the modules and perform input reading in such a fashion as to preserve, in a certain sense, the global properties of the system. Our approach is based on the theory of weakly endochronous systems, which gives criteria guaranteeing the existence of simple and efficient asynchronous wrappers. We focus on the transformation (by means of added signalling) of the synchronous modules of a multiclock synchronous specification into weakly endochronous modules, for which simple and efficient wrappers exist.

Compositional design of isochronous systems

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. This property, called endochrony or patience, 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. Compositionality can be achieved by weakening this objective, but at the cost of an exhaustive state-space exploration. This raises a trade-off between performance and precision. Our aim is to balance it by proposing a formal design methodology that adheres to a weakened global design objective: the non-blocking composition of weakly endochronous processes, while preserving local design objectives for synchronous modules. This yields an effective and cost-efficient approach to compositional synchronous modeling.

Separate Compilation of Polychronous Specifications

As code generation for synchronous programs requires strong safety properties to be satisfied, compositionality becomes a difficult goal to achieve. Most synchronous languages, such as Esterel, Lustre or Signal require a given module or compilation unit to be insensitive to latency that communication with its environment may incur. In Lustre or Signal, for instance, a compilation unit must satisfy the so-called property of endochrony. To preserve endochrony in an asynchronous environment, an ad-hoc protocol is synthesized to interface the module. However, endochrony is not preserved by composition. Consequently, the protocol has to be rebuilt every time a new module is added in the environment. We propose a methodology and code generation scheme which simplifies this concern. It consists of weakening the global objective of globally preserving endochrony. Instead, we aim at the preservation of a more liberal and compositional objective, weak endochrony [D. Potop-Butucaru and B. Caillaud and A. Benveniste. Concurrency in Synchronous Systems. In Formal Methods in System Design, v. 28(2). Springer, March 2006], which is compositional and much closer from the expected requirement of insensitivity to communication latency. As a result, our code generation scheme supports true separate compilation: a locally compiled synchronous module does not require its synthesized interface with the environment to be rebuilt once composed with another module.

Polychronous interpretation of synoptic, a domain specific modeling language for embedded flight-software

The SPaCIFY project, which aims at bringing advances in MDE to the satellite flight software indus- try, advocates a top-down approach built on a domain-specific modeling language named Synoptic. In line with previous approaches to real-time modeling such as Statecharts and Simulink, Synoptic features hierarchical decomposition of application and control modules in synchronous block dia- grams and state machines. Its semantics is described in the polychronous model of computation, which is that of the synchronous language SIGNAL.