Abstract — Twelve years ago, Proceedings of the IEEE devoted a special section to the synchronous languages. This article discusses the improvements, difficulties, and successes that have occured with the synchronous languages since then. Today, synchronous languages have been established as a technology of choice for modeling, specifying, validating, and implementing real-time embedded applications. The paradigm of synchrony has emerged as an engineer-friendly design method based on mathematicallysound tools.

Abstract. We propose a mathematical framework to deal with the composition of heterogeneous reactive systems. Our theory allows to establish theorems, from which design techniques can be derived. We illustrate this by two cases: the deployment of synchronous designs over GALS architectures, and the deployment of synchronous designs over the so-called Loosely Time-Triggered Architectures. 1

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We present a new block diagram language for describing synchronous software. It coordinates the execution of synchronous, concurrent software modules, allowing real-time systems to be assembled from precompiled blocks specified in other languages. The semantics we present, based on fixed points, is deterministic even in the presence of instantaneous feedback. The execution policy develops a static schedule—a fixed order in which to execute the blocks that makes the system execution predictable. We present exact and heuristic algorithms for finding schedules that minimize system execution time, and show that good schedules can be found quickly. The scheduling algorithms are applicable to other problems where large systems of equations need to be solved.

In this paper we introduce the notion of weak endochrony, which extends to a synchronous setting the classical theory of Mazurkiewicz traces. The notion is useful in the synthesis of correct-by-construction communication protocols for globally asynchronous, locally synchronous (GALS) systems. The independence between various computations can be exploited here to provide communication schemes that do not restrict concurrency while still guaranteeing correctness. 1.

We present several methods to generate modular code from synchronous hierarchical block diagrams. Modularity means code is generated for a given macro (i.e., composite) block independently from context, that is, without knowing where this block is to be used, and also with minimal knowledge about its sub-blocks. We achieve this by generating a set of interface functions for each block and a set of dependencies between these functions that is exported along with the interface. The main trade-off is the degree of modularity (number of interface functions) vs. reusability (the set of diagrams that the block can be used in without creating dependency cycles). 1

. The SACRES project is dealing with the development of new design methodologies and associated tools for safety critical embedded systems. Emphasis is put on formal techniques for modular verification of the specifications, distributed code generation, and generated code validation against specifications. This is allowed by using a single formal model which is that of the Dc+ format, which provides a common semantic framework for all tools as well as end user specification formalisms. Modular and distributed code generation is the main subject of this paper. Distributed code generation aims at reducing the dependency of the design with respect to the target architecture. Modularity helps reuse of existing designs, and makes it possible to address much larger systems. 1 Introduction The overall objective of the SACRES project is to provide designers of embedded control systems, in particular safety critical systems, with an enhanced design methodology supported by a toolset...

We present a compositional theory of heterogeneous reactive systems. The approach is based on the concept of tags marking the events of the signals of a system. Tags can be used for multiple purposes from indexing evolution in time (time stamping) to expressing relations among signals like coordination (e.g., synchrony and asynchrony), and causal dependencies. The theory provides flexibility in system modeling because it can be used both as a unifying mathematical framework to relate heterogeneous models of computations and as a formal vehicle to implement complex systems by combining heterogeneous components. In particular, we introduce an algebra of tag structures to define heterogeneous parallel composition formally. Morphisms between tag structures are used to define relationships between heterogeneous models at different levels of abstraction. In particular, they can be used to represent design transformations from tightly-synchronized specifications to loosely-synchronized implementations. The theory has an important application in the correct-by-construction deployment of synchronous design on distributed architectures.

We introduce the definition of a language of distributed reactive objects, a Behaviour Description Language (BDL), as a unified medium for specifying, verifying, compiling and validating object-oriented, distributed reactive systems. One of the novelties in BDL is its seamless integration into the Unified Modeling Language approach (UML). BDL supports a description of objects interaction which respects both the functional architecture of system designs and the declarative style of diagram descriptions. This support is implemented by means of a partial-order theoretical framework. This framework allows to specify both the causality and the control models of object interactions independently of any hypothesis on the actual conguration of the system. Given the description of such a configuration, the use of BDL offers new perspectives for a flexible verification of systems by modeling them as an asynchronous network of synchronous components. It allows an optimized code generation by using compil...