A Model for Real-Time Systems

In this paper we define an equivalence and a modal logic for real-time systems. The equivalence is based on timed processes and timing specifications they have to satisfy. While the equivalence we define is not a congruence, it does satisfy many law

Improved Algorithms for Parity and Streett objectives

The computation of the winning set for parity objectives and for Streett objectives in graphs as well as in game graphs are central problems in computer-aided verification, with application to the verification of closed systems with strong fairness conditions, the verification of open systems, checking interface compatibility, well-formedness of specifications, and the synthesis of reactive systems. We show how to compute the winning set on $n$ vertices for (1) parity-3 (aka one-pair Streett) objectives in game graphs in time $O(n^{5/2})$ and for (2) k-pair Streett objectives in graphs in time $O(n^2 + nk \log n)$. For both problems this gives faster algorithms for dense graphs and represents the first improvement in asymptotic running time in 15 years

Real-Time Estelle

Estelle is one of the standardized Formal Description Techniques for the specification of communication protocols and distributed systems. Unfortunately, Estelle is not capable to express real-time requirements or characteristics of services or protocols which is especially important in the context of distributed multimedia systems. In this paper, we introduce an extension to Estelle called Real-Time Estelle that allows to describe real-time systems. We introduce the syntax of the new language and propose both an operational and a descriptive semantics. Examples show the usefulness of the approach. We also discuss ways to implement Real-Time Estelle specifications

La importancia del uso de procesos físicos reales en la enseñanza universitaria de la ingeniería

Este artículo revisa nuestra experiencia en el uso de procesos reales en la enseñanza universitaria. En concreto describe los resultados obtenidos en un grupo de asignaturas basadas en los Sistemas de Tiempo Real, las cuales se imparten en varias escuelas de la Universidad Politécnica de Valencia. El hecho de impartir estas asignaturas en diversas titulaciones permite, en cierta forma, generalizar los beneficios que aportan los procesos físicos reales en el ámbito universitario con los resultados de una asignatura

A model for real-time systems and technique for verifying them using timed process algebra.

A model for real-time systems and technique for verifying them using timed process algebra

Automatic verification of real-time systems with discrete probability distributions

Abstract. We consider the timed automata model of [3], which allows the analysis of real-time systems expressed in terms of quantitative timing constraints. Traditional approaches to real-time system description express the model purely in terms of nondeterminism; however, we may wish to express the likelihood of the system making certain transitions. In this paper, we present a model for real-time systems augmented with discrete probability distributions. Furthermore, using the algorithm of [5] with fairness, we develop a model checking method for such models against temporal logic properties which can refer both to timing properties and probabilities, such as, “with probability 0.6 or greater, the clock x remains below 5 until clock y exceeds 2”.

Automatic verification of real-time systems with discrete probability distributions

We consider the timed automata model of Alur and Dill (Theoret. Comput. Sci. 126 (1994) 183–235), which allows the analysis of real-time systems expressed in terms of quantitative timing constraints. Traditional approaches to real-time system description express the model purely in terms of nondeterminism; however, it is often desirable to express the likelihood of the system making certain transitions. In this paper, we present a model for real-time systems augmented with discrete probability distributions. Furthermore, two approaches to model checking are introduced for this model. The first uses the algorithm of Baier and Kwiatkowska (Distributed Comput. 11 (1998) 125–155) to provide a verification technique against temporal logic formulae which can refer both to timing properties and probabilities. The second, generally more efficient, technique concerns the verification of probabilistic, real-time reachability properties

Automatic Verification of Real-time Systems with Discrete Probability Distributions ⋆

We consider the timed automata model of [3], which allows the analysis of realtime systems expressed in terms of quantitative timing constraints. Traditional approaches to real-time system description express the model purely in terms of nondeterminism; however, it is often desirable to express the likelihood of the system making certain transitions. In this paper, we present a model for real-time systems augmented with discrete probability distributions. Furthermore, two approaches to model checking are introduced for this model. The first uses the algorithm of [6] to provide a verification technique against temporal logic formulae which can refer both to timing properties and probabilities. The second, generally more efficient, technique concerns the verification of probabilistic, real-time reachability properties.

Timed automata with asynchronous processes: schedulability and decidability

Abstract. In this paper, we exend timed automata with asynchronous processes i.e. tasks triggered by events as a model for real-time systems. The model is expressive enough to describe concurrency and synchronization, and real time tasks which may be periodic, sporadic, preemptive or non-preemptive. We generalize the classic notion of schedulability to timed automata. An automaton is schedulable if there exists a scheduling strategy such that all possible sequences of events accepted by the automaton are schedulable in the sense that all associated tasks can be computed within their deadlines. We believe that the model may serve as a bridge between scheduling theory and automata-theoretic approaches to system modeling and analysis. Our main result is that the schedulability checking problem is decidable. To our knowledge, this is the first general decidability result on dense-time models for real time scheduling without assuming that preemptions occur only at integer time points. The proof is based on a decidable class of updatable automata: timed automata with subtraction in which clocks may be updated by subtractions within a bounded zone. The crucial observation is that the schedulability checking problem can be encoded as a reachability problem for such automata. Based on the proof, we have developed a symbolic technique and a prototype tool for schedulability analysis.

A Generic Approach to Schedulability Analysis of Real-Time Systems

This thesis presents a framework for design, analysis, and implementation of embedded systems. We adopt a model of timed automata extended with asynchronous processes i.e. tasks triggered by events. A task is an executable program characterized by its worst-case execution time and deadline, and possibly other parameters such as priorities etc. for scheduling. The main idea is to associate each location of an automaton with a task (or a set of tasks). A transition leading to a location denotes an event triggering the tasks and the clock constraint on the transition specifies the possible arrival times of the event. This yields a model for real-time systems expressive enough to describe concurrency and synchronization, and tasks with (or without) combinations of timing, precedence and resource constraints, which may be periodic, sporadic, preemptive and (or) non-preemptive. We believe that the model may serve as a bridge between scheduling theory and automata-theoretic approaches to system modelling and analysis. Our main result is that the schedulability checking problem for this model is decidable. To our knowledge, this is the first general decidability result on dense-time models for real time scheduling without assuming that preemptions occur only at integer time points. The proof is based on a decidable class of updatable automata: timed automata with subtraction in which clocks may be updated by subtractions within a bounded zone. As the second contribution, we show that for fixed priority scheduling strategy, the schedulability checking problem can be solved by reachability analysis on standard timed automata using only two extra clocks in addition to the clocks used in the original model to describe task arrival times. The analysis can be done in a similar manner to response time analysis in classic Rate-Monotonic Scheduling. We believe that this is the optimal solution to the problem. The third contribution is an extension of the above results to deal with precedence and resource constraints. We present an operational semantics for the model, and show that the related schedulability analysis problem can be solved efficiently using the same techniques. Finaly, to demonstrate the applicability of the framework, we have modelled, analysed, and synthesised the control software for a production cell. The presented results have been implemented in the Times tool for automated schedulability analysis and code synthesis