Team VerTeCs

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Section: New Results

Keywords : controller synthesis methodology, Hierarchical models, symbolic methods.

Controller Synthesis

Participant : Hervé Marchand.

Efficient Modular Method for the Control of Concurrent Discrete Event Systems: A Language-Based Approach

For several years we have been interested in the control of Concurrent Discrete Event Systems defined by a collection of components that interact with each other. We investigate the computation of the supremal controllable language contained in the language of the specification. We make the use of a modular centralized approach and perform the control on some approximations of the plant derived from the behavior of each component. The behavior of these approximations is restricted so that they respect a new language property for discrete event systems called partial controllability condition that depends on the safety property. It is shown that, under some assumptions (the objectives have to be locally consistent   [Oops!] ), the intersection of these “controlled approximations” corresponds to the supremal controllable language contained in the property with respect to the plant. This computation is performed without building the whole plant. Further, we relax the usual assumption that all shared events are controllable by introducing two new structural conditions relying on the global mutual controllability condition. The novel concept used as a sufficient structural condition is strong global mutual controllability. The main result uses a weaker condition called global mutual controllability together with local consistency of the specification. An example illustrates the approach. This work has been done in cooperation with Jan Komenda (Academy of Sciences, Brno, Czech Republic), Jan van Schuppen (CWI, The Netherlands) and Benoit Gaudin (UCD, Dublin)  [Oops!] .

Optimal discrete controller synthesis for the modeling of fault-tolerant distributed systems

Embedded systems require safe design methods based on formal methods, as well as safe execution based on fault-tolerance techniques. This year, we propose a safe design method for safe execution systems: it uses optimal discrete controller synthesis (DCS) to generate a correct reconfiguring fault-tolerant system. The properties enforced concern consistent execution, functionality fulfillment (whatever the faults, under some failure hypothesis), and several optimizations (of the tasks' execution time). We propose an algorithm for optimal DCS on bounded paths. We propose model patterns for a set of periodic tasks with checkpoints, a set of distributed, heterogeneous and fail-silent processors, and an environment model that expresses the potential fault patterns. We describe an implementation of our method, using the Sigali symbolic DCS tool and Mode Automata.This work has been done in cooperation with Emil Dumitrescu, Alain Girault and Eric Rutten  [Oops!] , [Oops!] , [Oops!] .

Ctrl-S Tool Development

This year, we have pursued, in collaboration with Sophie Pinchinat from the INRIA project S4 at IRISA, the development of the open platform, named Ctrl-S , dedicated to (1) the simulation of synchronous products of finite state machines, and (2) the integration of toolboxes that compute their controllers. This development has started in 2005 as a demo for the 30th Birthday of IRISA. Programming tasks have been assigned to Samer Maroun, an MSc. student from “École Supérieure d'ingénieurs de Beyrouth” (Liban), and was supported by an INRIA INTERSHIP. We also pursued the integration of the tool syntool, by considering new controller synthesis algorithms. A generic 3D libraries of components has been developped allowing an easy devising of demonstrations [Oops!] .


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