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New Results
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Section: New Results

Automatic distribution of synchronous programs

Participants : Mouaiad Alras, Gwenaël Delaval, Alain Girault [ contact person ] .

Modular distribution and application to discrete controller synthesis

Synchronous programming languages describe functionally centralized systems, where every value, input, output, or function are always directly available for every operation. However, most embedded systems are nowadays composed of several computing resources. The aim of this work is to provide a language-oriented solution to describe functionally distributed reactive systems. This is the topic of the PhD of Gwenaël Delaval, co-advised by Alain Girault and Marc Pouzet (University of Orsay, LRI)  [10] .

In order to address this problem, we have extended a synchronous data flow language with primitives for program distribution. These primitives allow the programmer, on one hand to describe the architecture of the system in terms of symbolic locations representing physical locations and links between them, and on the other hand to express where streams and expressions are located in this architecture  [23] .

First, a distributed semantics has been proposed in order to formalize the distributed execution of a program. Then, a type and effects system, where types of values are their localizations, has been proposed in order to infer the localization of non-annotated values by means of type inference and to ensure, at compilation time, the consistency of the distribution. Finally, a projection operation allows us to obtain automatically, from a centralized typed program, the local program to be executed by each computing resource. The semantical equivalence of the centralized program and its distributed version through this projection operation has been proven.

This type system, as well as the projection operation, has been implemented within the Lucid Synchrone [41] compiler. This higher-order synchronous language allows the expression of stream of stream functions. The distribution method proposed is performed in a modular way, and thus fits with the compilation of such higher-order features. The aim is, by combining this distribution method together with higher-order features of this languages, to allow the expression of dynamic reconfiguration of a hardware resource by another by sending code through communication channels: such channels being then streams of stream functions.

Furthermore, we have shown the application of the automatic distribution of synchronous reactive programs to the specific problem of discrete controller synthesis of complex reactive systems. Discrete controller synthesis is a formal method used to ensure properties on a flexible system which does not a priori verify them. However, this method is efficient only on Boolean programs. More complex embedded systems, comprising complex data types and structures, cannot be addressed without abstraction means. We show how such abstractions can be obtained automatically using a type-directed projection operation. This operation allows then the safe recombination of the result of the synthesis with the original abstracted system, preserving the ensured properties  [16] .

Model-based development of fault-tolerant embedded systems, code generation for distributed heterogeneous platforms

Model-based design (MBD) involves designing a model of a control system, simulating and debugging it with dedicated tools, and finally generating automatically code corresponding to this model. In the domain of embedded systems, it offers the huge advantage of avoiding the time-consuming and error-prone final coding phase. The main issue raised by MBD is the faithfulness of the generated code with respect to the initial model, the latter being defined by the simulation semantics. To bridge the gap between the high-level model and the low-level implementation, we use the synchronous programming language Lustre as an intermediary formal model [63] . Concretely, starting from a high-level model specified in the de-facto standard Simulink, we first generate Lustre code along with some necessary structured “glue code”, and then we generate embedded real-time code for the Xenomai RTOS ( ). Thanks to Lustre's clean mathematical semantics, we are able to guarantee the faithfulness of the generated multi-tasked real-time code. This is the topic of the PhD of Mouaiad Alras, co-advised by Alain Girault and Pascal Raymond (CNRS, Verimag).


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