74 research outputs found
Parametric Schedulability Analysis of Fixed Priority Real-Time Distributed Systems
Parametric analysis is a powerful tool for designing modern embedded systems,
because it permits to explore the space of design parameters, and to check the
robustness of the system with respect to variations of some uncontrollable
variable. In this paper, we address the problem of parametric schedulability
analysis of distributed real-time systems scheduled by fixed priority. In
particular, we propose two different approaches to parametric analysis: the
first one is a novel technique based on classical schedulability analysis,
whereas the second approach is based on model checking of Parametric Timed
Automata (PTA).
The proposed analytic method extends existing sensitivity analysis for single
processors to the case of a distributed system, supporting preemptive and
non-preemptive scheduling, jitters and unconstrained deadlines. Parametric
Timed Automata are used to model all possible behaviours of a distributed
system, and therefore it is a necessary and sufficient analysis. Both
techniques have been implemented in two software tools, and they have been
compared with classical holistic analysis on two meaningful test cases. The
results show that the analytic method provides results similar to classical
holistic analysis in a very efficient way, whereas the PTA approach is slower
but covers the entire space of solutions.Comment: Submitted to ECRTS 2013 (http://ecrts.eit.uni-kl.de/ecrts13
A Benchmarks Library for Extended Parametric Timed Automata
Parametric timed automata are a powerful formalism for reasoning on
concurrent real-time systems with unknown or uncertain timing constants. In
order to test the efficiency of new algorithms, a fair set of benchmarks is
required. We present an extension of the IMITATOR benchmarks library, that
accumulated over the years a number of case studies from academic and
industrial contexts. We extend here the library with several dozens of new
benchmarks; these benchmarks highlight several new features: liveness
properties, extensions of (parametric) timed automata (including stopwatches or
multi-rate clocks), and unsolvable toy benchmarks. These latter additions help
to emphasize the limits of state-of-the-art parameter synthesis techniques,
with the hope to develop new dedicated algorithms in the future.Comment: This is the author (and extended) version of the manuscript of the
same name published in the proceedings of the 15th International Conference
on Tests and Proofs (TAP 2021
Dynamic Clock Elimination in Parametric Timed Automata
The formalism of parametric timed automata provides designers with a formal way to specify and verify real-time concurrent systems where iming requirements are unknown (or parameters). Such models are usually subject to the state space explosion. A popular way to partially reduce the size of the state space is to reduce the number of clock variables. In this work, we present a technique for dynamically eliminating clocks. Experiments using IMITATOR show a diminution of the number of states and of the computation time, and in some cases allow termination of the analysis of models that could not terminate otherwise. More surprisingly, even when the number of clocks remains constant, there is little noticeable overhead in applying the proposed clock elimination
Timed Automata Robustness Analysis via Model Checking
Timed automata (TA) have been widely adopted as a suitable formalism to model
time-critical systems. Furthermore, contemporary model-checking tools allow the
designer to check whether a TA complies with a system specification. However,
the exact timing constants are often uncertain during the design phase.
Consequently, the designer is often able to build a TA with a correct
structure, however, the timing constants need to be tuned to satisfy the
specification. Moreover, even if the TA initially satisfies the specification,
it can be the case that just a slight perturbation during the implementation
causes a violation of the specification. Unfortunately, model-checking tools
are usually not able to provide any reasonable guidance on how to fix the model
in such situations. In this paper, we propose several concepts and techniques
to cope with the above mentioned design phase issues when dealing with
reachability and safety specifications
Verification and Parameter Synthesis for Real-Time Programs using Refinement of Trace Abstraction
We address the safety verification and synthesis problems for real-time
systems. We introduce real-time programs that are made of instructions that can
perform assignments to discrete and real-valued variables. They are general
enough to capture interesting classes of timed systems such as timed automata,
stopwatch automata, time(d) Petri nets and hybrid automata.
We propose a semi-algorithm using refinement of trace abstractions to solve
both the reachability verification problem and the parameter synthesis problem
for real-time programs.
All of the algorithms proposed have been implemented and we have conducted a
series of experiments, comparing the performance of our new approach to
state-of-the-art tools in classical reachability, robustness analysis and
parameter synthesis for timed systems. We show that our new method provides
solutions to problems which are unsolvable by the current state-of-the-art
tools
From Authored to Produced Time in Computer-Musician Interactions
International audienceHuman musicians have since long developed methods and formalisms for ensemble authoring and real-time coordination and synchronization of their actions. Bringing such capabilities to computers and providing them with the ability to take part in musical interactions with human musicians, poses interesting challenges for authoring of time and interaction and real-time coordination that we address in this paper in the context of Mixed Music and the Antescofo project
A thread synchronization model for the PREEMPT_RT Linux kernel
This article proposes an automata-based model for describing and validating sequences of kernel events in Linux PREEMPT_RT and how they influence the timeline of threads’ execution, comprising preemption control, interrupt handling and control, scheduling and locking. This article also presents an extension of the Linux tracing framework that enables the tracing of kernel events to verify the consistency of the kernel execution compared to the event sequences that are legal according to the formal model. This enables cross-checking of a kernel behavior against the formalized one, and in case of inconsistency, it pinpoints possible areas of improvement of the kernel, useful for regression testing. Indeed, we describe in details three problems in the kernel revealed by using the proposed technique, along with a short summary on how we reported and proposed fixes to the Linux kernel community. As an example of the usage of the model, the analysis of the events involved in the activation of the highest priority thread is presented, describing the delays occurred in this operation in the same granularity used by kernel developers. This illustrates how it is possible to take advantage of the model for analyzing the preemption model of Linux
Hackers vs. Security: Attack-Defence Trees as Asynchronous Multi-Agent Systems
Attack-Defence Trees (ADTs) are well-suited to assess possible attacks to
systems and the efficiency of counter-measures. In this paper, we first enrich
the available constructs with reactive patterns that cover further security
scenarios, and equip all constructs with attributes such as time and cost to
allow quantitative analyses. Then, ADTs are modelled as (an extension of)
Asynchronous Multi-Agents Systems--EAMAS. The ADT-EAMAS transformation is
performed in a systematic manner that ensures correctness. The transformation
allows us to quantify the impact of different agents configurations on metrics
such as attack time. Using EAMAS also permits parametric verification: we
derive constraints for property satisfaction. Our approach is exercised on
several case studies using the Uppaal and IMITATOR tools.Comment: This work was partially funded by the NWO project SEQUOIA (grant
15474), EU project SUCCESS (102112) and the PHC van Gogh PAMPAS. The work of
Arias and Petrucci has been supported by the BQR project AMoJA
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