Paul Caspi

The synchronous data flow programming language LUSTRE

The authors describe LUSTRE, a data flow synchronous language designed for programming reactive systems-such as automatic control and monitoring systems-as well as for describing hardware. The data flow aspect of LUSTRE makes it very close to usual description tools in these domains (block-diagrams, networks of operators, dynamical sample-systems, etc.), and its synchronous interpretation makes it well suited for handling time in programs. Moreover, this synchronous interpretation allows it to be compiled into an efficient sequential program. The LUSTRE formalism is very similar to temporal logics. This allows the language to be used for both writing programs and expressing program properties, which results in an original program verification methodology. >

The synchronous languages 12 years later

Twelve years ago, Proceedings of the IEEE devoted a special section to the synchronous languages. This paper 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 mathematically sound tools.

LUSTRE: a declarative language for real-time programming

LUSTRE is a synchronous data-flow language for programming systems which interact with their environments in real-time. After an informal presentation of the language, we describe its semantics by means of structural inference rules. Moreover, we show how to use this semantics in order to generate efficient sequential code, namely, a finite state automaton which represents the control of the program. Formal rules for program transformation are also presented.

Translating discrete-time simulink to lustre

We present a method of translating discrete-time Simulink models to Lustre programs. Our method consists of three steps: type inference, clock inference, and hierarchical bottom-up translation. In the process, we explain and formalize the typing and timing mechanisms of Simulink. The method has been implemented in a prototype tool called S2L, which has been used in the context of a European research project to translate two automotive controller models provided by Audi.

Timed Regular Expressions

In this article, we define timed regular expressions, a formalism for specifying discrete behaviors augmented with timing information, and prove that its expressive power is equivalent to the timed automata of Alur and Dill. This result is the timed analogue of Kleene Theorem and, similarly to that result, the hard part in the proof is the translation from automata to expressions. This result is extended from finite to infinite (in the sense of Büchi) behaviors. In addition to these fundamental results, we give a clean algebraic framework for two commonly accepted formalisms for timed behaviors, time-event sequences and piecewise-constant signals.

A Kleene theorem for timed automata

In this paper we define timed regular expressions, and extension of regular expressions for specifying sets of dense-time discrete-valued signals. We show that this formalism is equivalent in expressive power to the timed automata of Alur and Dill by providing a translation procedure from expressions to automata and vice versa. the result is extended to /spl omega/-regular expressions (Buchis theorem).

Implementing Synchronous Models on Loosely Time Triggered Architectures

Synchronous systems offer a clean semantics and an easy verification path at the expense of often inefficient implementations. Capturing design specifications as synchronous models and then implementing the specifications in a less restrictive platform allow to address a much larger design space. The key issue in this approach is maintaining semantic equivalence between the synchronous model and its implementation. We address this problem by showing how to map a synchronous model onto a loosely time-triggered architecture that is fairly straightforward to implement as it does not require global synchronization or blocking communication. We show how to maintain semantic equivalence between specification and implementation using an intermediate model (similar to a Kahn process network but with finite queues) that helps in defining the transformation. Performance of the semantic preserving implementation is studied for the general case as well as for a few special cases.

A Protocol for Loosely Time-Triggered Architectures

A distributed real-time control system has a time-triggered nature, just because the physical system for control is bound to physics. Loosely Time-Triggered Architectures (LTTA) are a weaker form of the strictly synchronous Time-Triggered Architecture proposed by Kopetz, in which the different periodic clocks are not synchronized, and thus may suffer from relative offset or jitter.We propose a protocol that ensures a coherent system of logical clocks on the top of LTTA, and we provide several proofs for it, both manual and automatic, based on synchronous languages and associated model checkers. We briefly discuss how this can be used for correct deployment of synchronous designs on an LTTA.

Guidelines for a graduate curriculum on embedded software and systems

The design of embedded real-time systems requires skills from multiple specific disciplines, including, but not limited to, control, computer science, and electronics. This often involves experts from differing backgrounds, who do not recognize that they address similar, if not identical, issues from complementary angles. Design methodologies are lacking in rigor and discipline so that demonstrating correctness of an embedded design, if at all possible, is a very expensive proposition that may delay significantly the introduction of a critical product. While the economic importance of embedded systems is widely acknowledged, academia has not paid enough attention to the education of a community of high-quality embedded system designers, an obvious difficulty being the need of interdisciplinarity in a period where specialization has been the target of most education systems. This paper presents the reflections that took place in the European Network of Excellence Artist leading us to propose principles and structured contents for building curricula on embedded software and systems.

Toward an Approximation Theory for Computerised Control

This paper addresses the question of extending the usual approximation and sampling theory of continuous signals and systems to those encompassing discontinuities, such as found in modern complex control systems (mode switches for instance). We provide some evidence that the Skorokhod topology is a good candidate for dealing with those cases in a uniform manner by showing that, in the boolean case, Skorokhod uniformly continuous signals are exactly the signals with uniform bounded variability.