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25
TIMES: a Tool for Schedulability Analysis and Code Generation of RealTime Systems
 IN PROC. OF FORMATS’03, NUMBER 2791 IN LNCS
, 2003
"... Times is a tool suite designed mainly for symbolic schedulability analysis and synthesis of executable code with predictable behaviours for realtime systems. Given a system design model consisting of (1) a set of application tasks whose executions may be required to meet mixed timing, precedenc ..."
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Cited by 85 (2 self)
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Times is a tool suite designed mainly for symbolic schedulability analysis and synthesis of executable code with predictable behaviours for realtime systems. Given a system design model consisting of (1) a set of application tasks whose executions may be required to meet mixed timing, precedence, and resource constraints, (2) a network of timed automata describing the task arrival patterns and (3) a preemptive or nonpreemptive scheduling policy, Times will generate a scheduler, and calculate the worst case response times for the tasks.
Almost ASAP Semantics: From Timed Models to Timed Implementations
, 2003
"... In this paper, we introduce a parametric semantics for timed controllers called the Almost ASAP semantics. This semantics is a relaxation of the usual ASAP semantics (also called the maximal progress semantics) which is a mathematical idealization that can not be implemented by any physical devic ..."
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Cited by 53 (6 self)
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In this paper, we introduce a parametric semantics for timed controllers called the Almost ASAP semantics. This semantics is a relaxation of the usual ASAP semantics (also called the maximal progress semantics) which is a mathematical idealization that can not be implemented by any physical device no matter how fast it is. On the contrary, any correct Almost ASAP controller can be implemented by a program on a hardware if this hardware is fast enough. We study the properties of this semantics, show how it can be analyzed using the tool HyTech, and illustrate its practical use on examples.
Implementation of timed automata: an issue of semantics or modeling
 In Proc. 3rd Int. Conf. Formal Modelling and Analysis of Timed Systems (FORMATS’05), Lecture Notes in Computer Science
, 2005
"... Abstract. We examine to what extent implementation of timed automata can be achieved using the standard semantics and appropriate modeling, instead of introducing new semantics. We propose an implementation methodology which allows to transform a timed automaton into a program and to check whether t ..."
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Cited by 33 (3 self)
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Abstract. We examine to what extent implementation of timed automata can be achieved using the standard semantics and appropriate modeling, instead of introducing new semantics. We propose an implementation methodology which allows to transform a timed automaton into a program and to check whether the execution of this program on a given platform satisfies a desired property. This is done by modeling the program and the execution platform, respectively, as an untimed automaton and a collection of timed automata. We also study the problem of property preservation, in particular when moving to a “better” execution platform. We show that some subtleties arise regarding the definition of “better”, in particular for digital clocks. The fundamental issue is that faster clocks result in better “sampling ” and therefore can introduce more behaviors. 1
Schedulability analysis of fixedpriority systems using timed automata
 Theoretical Computer Science
, 2006
"... In classic scheduling theory, realtime tasks are usually assumed to be periodic, i.e. tasks are released and computed with fixed rates periodically. To relax the stringent constraints on task arrival times, we propose to use timed automata to describe task arrival patterns. In a previous work, it i ..."
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Cited by 32 (5 self)
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In classic scheduling theory, realtime tasks are usually assumed to be periodic, i.e. tasks are released and computed with fixed rates periodically. To relax the stringent constraints on task arrival times, we propose to use timed automata to describe task arrival patterns. In a previous work, it is shown that the general schedulability checking problem for such models is a reachability problem for a decidable class of timed automata extended with subtraction. Unfortunately, the number of clocks needed in the analysis is proportional to the maximal number of schedulable task instances associated with a model, which is in many cases huge. In this paper, we show that for fixed priority scheduling strategy, the schedulability checking problem can be solved using standard timed automata with 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 RateMonotonic Analysis (RMA). The result is further extended to systems with datadependent control, in which the release time of a task may depend on the timepoint at which other tasks finish their execution. For the case when the execution times of tasks are constants, we show that the schedulability problem can be solved using n+ 1 extra clocks, where n is the number of tasks. The presented analysis techniques have been implemented in the Times tool. For systems with only periodic tasks, the performance of the tool is comparable with tools implementing the classic RMA technique based on equationsolving, without suffering from the exponential explosion in the number of tasks.
Robustness and Implementability of Timed Automata
 In Proc. Joint Conf. Formal Modelling and Analysis of Timed Systems and Formal Techniques in RealTime and Fault Tolerant System (FORMATS+FTRTFT’04), volume 3253 of LNCS
, 2004
"... In a former paper, we de ned a new semantics for timed automata, the Almost ASAP semantics, which is parameterized by to cope with the reaction delay of the controller. We showed that this semantics is implementable provided there exists a strictly positive value for the parameter for which t ..."
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Cited by 25 (13 self)
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In a former paper, we de ned a new semantics for timed automata, the Almost ASAP semantics, which is parameterized by to cope with the reaction delay of the controller. We showed that this semantics is implementable provided there exists a strictly positive value for the parameter for which the strategy is correct. In this paper, we de ne the implementability problem to be the question of existence of such a . We show that this question is closely related to a notion of robustness for timed automata de ned in [Pur98] and prove that the implementability problem is decidable.
A generic approach to schedulability analysis of realtime tasks
 Nordic J. of Computing
, 2003
"... Abstract. In offline schedulability tests for real time systems, tasks are usually assumed to be periodic, i.e. they are released with fixed rates. To relax the assumption of complete knowledge on arrival times, we propose to use timed automata to describe task arrival patterns. In a recent work, i ..."
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Cited by 24 (2 self)
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Abstract. In offline schedulability tests for real time systems, tasks are usually assumed to be periodic, i.e. they are released with fixed rates. To relax the assumption of complete knowledge on arrival times, we propose to use timed automata to describe task arrival patterns. In a recent work, it is shown that for fixed priority scheduling strategy and tasks with only timing constraints (i.e. execution time and deadline), the schedulability of such models can be checked by reachability analysis on timed automata with two clocks. In this paper, we extend the above result to deal with precedence and resource constraints. This yields a unified task model, which is expressive enough to describe concurrency, synchronization, and tasks that may be periodic, aperiodic, preemptive or nonpreemptive with (or without) combinations of timing, 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 technique. The presented results have been implemented in the TIMES tool for automated schedulability analysis. 1
Schedulability analysis using two clocks
 In: 9th International Conference on Tools and Algorithms for the Construction and Analysis of Systems (TACAS 2003) (Hubert Garavel and John Hatcliff, Eds.). Vol. 2619 of LNCS. SpringerVerlag
, 2003
"... Abstract. In classic scheduling theory, realtime tasks are usually assumed to be periodic, i.e. tasks arrive and compute with fixed rates periodically. To relax the stringent constraints on task arrival times, we propose to use timed automata to describe task arrival patterns. In a previous work, ..."
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Cited by 19 (3 self)
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Abstract. In classic scheduling theory, realtime tasks are usually assumed to be periodic, i.e. tasks arrive and compute with fixed rates periodically. To relax the stringent constraints on task arrival times, we propose to use timed automata to describe task arrival patterns. In a previous work, it is shown that the general schedulability checking problem for such models is a reachability problem for a decidable class of timed automata extended with subtraction. Unfortunately, the number of clocks needed in the analysis is proportional to the maximal number of schedulable task instances associated with a model, which in many cases is huge. In this paper, 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 RateMonotonic Scheduling. We believe that this is the optimal solution to the problem, a problem that was suspected undecidable previously. We also extend the result to systems in which the timed automata and the tasks may read and update shared data variables. Then the release timepoint of a task may depend on the values of the shared variables, and hence on the timepoint at which other tasks finish their exection. We show that this schedulability problem can be encoded as timed automata using n+1 extra clocks, where n is the number of tasks. 1
Robust Safety of Timed Automata
 FORMAL METHODS IN SYSTEM DESIGN
"... Timed automata are governed by an idealized semantics that assumes a perfectly precise behavior of the clocks. The traditional semantics is not robust because the slightest perturbation in the timing of actions may lead to completely different behaviors of the automaton. Following several recent wo ..."
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Cited by 16 (8 self)
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Timed automata are governed by an idealized semantics that assumes a perfectly precise behavior of the clocks. The traditional semantics is not robust because the slightest perturbation in the timing of actions may lead to completely different behaviors of the automaton. Following several recent works, we consider a relaxation of this semantics, in which guards on transitions are widened by ∆> 0 and clocks can drift by ε> 0. The relaxed semantics encompasses the imprecisions that are inevitably present in an implementation of a timed automaton, due to the finite precision of digital clocks. We solve the safety verification problem for this robust semantics: given a timed automaton and a set of bad states, our algorithm decides if there exist positive values for the parameters ∆ and ε such that the timed automaton never enters the bad states under the relaxed semantics.
Verification of Computation Orchestration via Timed Automata
 Proc. of the 8 th Int. Conference on Formal Engineering Methods, volume 4260 of Lecture Notes in Computer Science
, 2006
"... Abstract. Recently, a promising programming model called Orc has been proposed to support a structured way of orchestrating distributed web services. Orc is intuitive because it offers concise constructors to manage concurrent communication, timeouts, priorities, failure of sites or communication a ..."
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Cited by 14 (3 self)
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Abstract. Recently, a promising programming model called Orc has been proposed to support a structured way of orchestrating distributed web services. Orc is intuitive because it offers concise constructors to manage concurrent communication, timeouts, priorities, failure of sites or communication and so forth. The semantics of Orc is also precisely defined. However, there is no verification tool available to verify critical properties against Orc models. Instead of building one from scratch, we believe the existing mature modelcheckers can be reused. In this work, we first define a Timed Automata semantics for the Orc language, which we prove is semantically equivalent to the original operational semantics of Orc. Consequently, Timed Automata models are systematically constructed from Orc models. The practical implication of the construction is that tool supports for Timed Automata, e.g., UPPAAL, can be used to model check Orc models. An experimental tool is implemented to automate our approach. 1
Assurance cases in modeldriven development of the pacemaker software
 In Proceedings of International Symposium on Leveraging Applications of Formal Methods, Verification, and Validation (ISoLA 2010), volume 6416 of LNCS
, 2010
"... of the Pacemaker Software ⋆ ..."
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