Publications 1997

P. Aubry.
Mises en oeuvre distribuées de programmes synchrones.  Phd thesis, Université de Rennes 1, IFSIC, October 1997. (postscript)
Abstract : L'approche synchrone est destinée aux programmeurs des systèmes réactifs temps-réel. En apportant des primitives de concurrence et de communication, les langages synchrones, tels que SIGNAL, LUSTRE ou ESTEREL, permettent une spécification des systèmes à un haut niveau d'abstraction; basés sur une sémantique forte, ils offrent les possibilités de vérification formelle et d'optimisations poussées. Cette thèse se place dans le cadre de l'environnement SIGNAL en explorant la répartition manuelle et semi-automatique de programmes flots-de-données synchrones. L'étude, basée sur un modèle dynamique, permet de combler les manques de la description statique habituellement utilisée. Ce modèle permet ainsi de décrire des exécutions synchronisées et désynchronisées, respectant tout ou partie de la sémantique synchrone traditionnelle. Le prototype réalisé dans le cadre de ce travail met l'accent sur l'automatisation et la transparence des mécanismes de distribution, en introduisant les directives de répartition au sein même du langage SIGNAL.
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PH. Baufreton, X. Méhaut, E. Rutten.
L'approche Sacres pour les systèmes embarqués à sécurité critique.  Actes du Salon Real-Time Systems RTS'97, Paris, Teknea, pages 101-118, January 1997. (postscript)
Abstract : Cet article présente une approche pour la conception et mise en oeuvre de systèmes embarqués à sécurité critique développée dans le projet Esprit Sacres. Le but du projet est d'intégrer dans un environnement complet et unifié une variété d'outils de spécification tels que StateMate, Sildex, les Timing Diagrams et un outil de vérification. Nous nous focaliserons ici sur le domaine d'application de la motorisation en avionique, et de l'utilisation de l'outil Sildex.
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PH. Baufreton, X. Méhaut, E. Rutten.
Embedded Systems in Avionics and the Sacres Approach.  Proceedings of The 16th International Conference on Computer Safety, Reliability and Security, SAFECOMP'97, York, United Kingdom, Springer, September 1997. (postscript)
Abstract : This paper presents an industrial experiment in avionics of the programming environment Sildex based on the synchronous model, and an approach to the design and implementation of such safety critical embedded systems, developped in the framework of the Esprit project Sacres. The goal of the project is to integrate into a complete and unified environment, around the synchronous models technology, a variety of specification tools such as StateMate, Sildex, Timing Diagrams and tools for verification, code generation and validation of the code produced.
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PH. Baufreton, H. Granier, X. Méhaut, E. Rutten.
The Sacres Approach to Emdedded Systems Applied to Aircraft Engine Controllers.  Proceedings of the 22st IFAC/IFIP Workshop on Real Time Programming, WRTP'97, Lyon, France, Elsevier, September 1997. (postscript)
Abstract : This paper presents an industrial experiment in avionics of the programming environment Sildex based on the synchronous model, and an approach to the design and implementation of such safety critical embedded systems, developped in the framework of the Esprit project Sacres. The goal of the project is to integrate into a complete and unified environment, around the synchronous models technology, a variety of specification tools such as StateMate, Sildex, Timing Diagrams and tools for verification, code generation and validation of the code produced. This design environment is used at SNECMA in the various steps of the development of controllers for aircraft engines.
Keywords: Reactive systems, design environment, synchronous language, industrial application, aircraft engine control.

A. Benveniste, P. Le Guernic, P. Aubry.
Compositionality in dataflow synchronous languages: specification & code generation.  Research report Irisa / Inria-Rennes, No3310, November 1997. (postscript)
Abstract : Modularity is advocated as a solution for the design of large systems, the mathematical translation of this concept is often that of compositionality. This paper is devoted the issues of compositionality aiming at modular code generation, for dataflow synchronous languages. As careless storing of object code for further reuse in systems design fails to work, we first concentrate on what are the additional features needed to abstract programs for the purpose of code generation: we show that a central notion is that of scheduling specification as resulting from a causality analysis of the given program. Then we study separate compilation for synchronous programs, and we discuss the issue of distributed implementation using an asynchronous medium of communication; for both topics we provide a complete formal study. Corresponding algorithms are currently under development in the framework of the DC+ common format for synchronous languages.
Keywords: Synchronous languages, modularity, compositionality, code generation, distributed code generation, causality analysis, separate compilation, desynchronisation

P. Bournai, M. Le Borgne, H. Marchand.
Environnement de conception d'automatismes discrets basé sur le langage Signal.  Research report Irisa, No1124, September 1997. (postscript)
Abstract : Nous présentons l'intégration des techniques de vérification et de synthèse de contrôleurs dans l'environnement de programmation Signal à travers la description d'un prototype pour la conception d'automatismes et de logiciels s\^urs les implémentant. Ce prototype est validé à travers divers exemples tirés du monde académique.

Keywords: Théorie du contrôle, systèmes dynamiques polynomiaux, méthodologie synchrine, Signal, simulation

E. Marchand, E. Rutten, F. Chaumette.
From data-flow task to multi-tasking: Applying the synchronous approach to active vision in robotics.  IEEE Trans. on Control Systems Technology, 5(2):200-216, March 1997. (postscript)
Abstract : In this paper, we apply the synchronous approach to real time active visual 3D reconstruction using a camera mounted on a robot end-effector. It illustrates the adequateness of SIGNAL, a synchronous data flow programming language and environment, for the specification of a system dealing with various domains in control theory and computer vision. More precisely, our application consists in the 3D structure estimation of a set of geometrical primitives using an active vision paradigm. At the level of camera motion control, the visual servoing approach is specified and implemented in SIGNAL as a function from sensor inputs to control outputs. Furthermore, the 3D structure estimation method is based on the ``structure from controlled motion'' approach (constraining camera motion for optimal estimation). Its specification is made in parallel to visual servoing, and involves the delay mechanism of SIGNAL for the specification of filters. This reconstruction involves to be focused on each object; we thus present a perception strategy for sequencing several estimations, using task preemption and time intervals in SIGNAL. It allows to consider in an unified framework the various aspects of the application: from data-flow task specification to multi-tasking and hierarchical task preemption. The integration of these techniques is validated experimentally by their implementation on a robotic cell. Merits and drawbacks of the proposed framework with respect to more usual asynchronous approaches are finally discussed.

H. Marchand, M. Le Borgne.
Partial Order Control and Optimal Control of Discrete Event Systems modeled as Polynomial Dynamical Systems over Galois fields.  Research report Irisa, No1125, October 1997. (postscript)
Abstract : In this paper, we propose computational methods for the synthesis of controllers for Discrete Event Systems modeled as Polynomial Dynamical Systems over finite Galois field. The control objectives are specified as order relations to be checked and as a minimization of a given cost function over the states through the trajectories of the system. The control objectives are then synthesized using algebraic tools such as ideals, varieties and morphisms. The applications of these methods to the safety specification of a power transformer station controller is finally presented.

Keywords: Discrete Event Systems, Polynomial methods, synthesis, Optimal Control.

H. Marchand.
Méthodes de synthèse d'automatismes décrits par des systèmes à événements discrets finis.  Phd thesis, Université de Rennes 1, IFSIC, October 1997. (postscript)
Abstract : Le langage SIGNAL est destiné à la conception et à la mise en oeuvre sure de systèmes réactifs temps réels. Certains domaines d'application exigent une grande fiabilité et une sûreté de fonctionnement. Traditionnellement, ces exigences sont vérifiées a posteriori par des techniques de simulation et de vérification de propriétés. La théorie du contrôle, utilisée dans le cadre des systèmes à événements discrets permet de développer le système en utilisant des méthodes de construction garantissant a priori les propriétés attendues du système global, permettant ainsi de restreindre la phase de validation aux seules propriétés du système non garanties par construction. L'objectif de cette thèse est la mise au point de méthodes permettant de dériver un système en y intégrant un ensemble de propriétés logico-temporelles. Dans notre approche, la théorie du contrôle repose sur une représentation équationnelle de la partie logique d'un programme SIGNAL sous la forme d'un système dynamique polynomial dans Z/3Z. Nous montrons, dans ce rapport, comment à partir d'un tel système, il est possible de synthétiser un contrôleur de manière à ce que le système contrôlé vérifie a posteriori un objectif de commande logique. Nous présentons une théorie de la commande optimale, permettant de synthétiser des contrôleurs traduisant un critère qualitatif et non plus logique. Les objectifs de commande s'expriment alors comme des relations d'ordre ou comme un critère de minimisation sur une trajectoire bornée du système. Enfin du point de vue théorique, nous esquissons une méthode de contrôle de systèmes dynamiques polynomiaux partiellement observés. Finalement, nous présentons l'intégration de ces techniques dans l'environnement de programmation SIGNAL à travers la description d'un prototype pour la conception d'automatismes et de logiciel sûrs les implémentant. Ce prototype est validé sur le contrôle d'un poste de transformation électrique et à travers divers exemples tirés du monde académique.
Keywords: Systèmes à événements discrets, théorie du contrôle, commande optimale, langages synchrones, SIGNAL

D. Nowak, J.P. Talpin, T. Gautier, P. Le Guernic.
An ML-like module system for the synchronous language Signal.  European Conference on Parallel Processing (Euro-Par'97), Springer-Verlag, LNCS 1300, pages 1244-1253, August 1997. (postscript)
Abstract : Synchronous languages, such as SIGNAL, are best suited for the design of dependable real-time systems. Synchronous languages enable a very high-level specification and an extremely modular implementation of complex systems by structurally decomposing them into elementary synchronous processes. Separate compilation in reactive languages is however made a difficult issue by global safety requirements. To enable separate compilation of the functional components of reactive systems while preserving their global integrity, we introduce a module system for SIGNAL. Just as data-types describe the invariants of program modules in functional languages, temporal and data-flow invariants interface SIGNAL processes to their environment. In conventional languages, typing is the medium allowing the separate compilation of functions in a program. In SIGNAL, the notion of conditional data-flow graph can similarly be used for separately compiling reactive processes and for assembling them in complex systems. Following this principle, we present the first design and implementation of a polymorphic type system and of a module system for the synchronous language SIGNAL.
Keywords: synchronous programming, module system, type system

D. Nowak, J.P. Talpin, T. Gautier.
Un système de modules avancé pour Signal.  Research report Irisa / Inria-Rennes, No3176, June 1997. (postscript)
Abstract : Nous proposons un système de modules avancé pour SIGNAL permettant de définir des unités génériques, des types abstraits et de paramétrer les modules par d'autres modules. La première tâche a été de formaliser le typage de SIGNAL sous forme de règles d'inférences, puis d'en déduire un algorithme de synthèse automatique des types.
Keywords: programmation synchrone, système de module, système de type

S. Pinchinat, J.V. Echague.
SOS specifications and Compositional ST-semantics.  XXIII Conferencia Latinoamericana de Informatica, Valparaiso, Chili, November 1997. (postscript)
Abstract : Syntactic formats of SOS specifications as a criterion to obtain compositional semantics have widely been investigated, almost always in the interleaving setting. In this paper, we study the case of truly concurrent semantics. We show how to derive Asynchronous Transition Systems with invisible actions from SOS specifications, and we exhibit simple syntactic conditions over the specifications to get compositionality for (rooted) ST-semantics. Classical process description languages like CCS fit the conditions.
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E. Rutten, E. Marchand, F. Chaumette.
An experiment with reactive data-flow tasking in active robot vision.  Software - Practice & Experience, 27(5):599-621, May 1997. (postscript)
Abstract :

This paper presents an experiment with the synchronous approach to reactive systems programming, and particularly the Signal language, applied to a significant problem in robot vision: active visual reconstruction. This application consists of the specification of a system dealing with various domains such as robot control, computer vision and transitions between different modes of control. It illustrates the adequacy in such domains of Signal, a data flow programming language and environment. The programming environment features tools for formal specification, analysis, consistency checking and code generation. Signal and its language-level extension for task preemption SignalGTi are used at the different levels of the application: data-flow function for the camera motion control (visual servoing), reconstruction method (in parallel to visual servoing, involving the dynamical processes), and reconstruction of complex scenes (with transitions between several robotics tasks). The combination of these levels constitutes a hybrid behavior with (sampled) continuous control and discrete transitions. These techniques are validated experimentally by an implementation on a robotic cell.
 

Keywords:
formal specification language, reactive systems, data flow, task preemption, robotics, active vision.

I. Smarandache, P. Le Guernic.
A Canonical Form for Affine Relations in Signal.  Research report Irisa / Inria-Rennes, No3097, February 1997. (postscript)
Abstract : In this paper we present affine transformations as an extension of the Signal language for the specification and validation of real-time applications. A Signal program is a system of equations which specify dependencies between program data and synchronization constraints on clock variables. In order to test if a program is functionally safe, the Signal compiler resolves the clock constraints and verifies that the data dependency graph contains no cycles. By means of the new transformations, {\it affine relations

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