Fast algorithms for handling diagonal constraints in timed automata

A popular method for solving reachability in timed automata proceeds by enumerating reachable sets of valuations represented as zones. A na\"ive enumeration of zones does not terminate. Various termination mechanisms have been studied over the years. Coming up with efficient termination mechanisms has been remarkably more challenging when the automaton has diagonal constraints in guards. In this paper, we propose a new termination mechanism for timed automata with diagonal constraints based on a new simulation relation between zones. Experiments with an implementation of this simulation show significant gains over existing methods.Comment: Shorter version of this article to appear in CAV 201

Performance Analysis and Functional Verification of the Stop-and-Wait Protocol in HOL

Real-time systems usually involve a subtle interaction of a number of distributed components and have a high degree of parallelism, which makes their performance analysis quite complex. Thus, traditional techniques, such as simulation, or the state-based formal methods usually fail to produce reasonable results. In this paper, we propose to use higher-order-logic (HOL) theorem proving for the performance analysis of real-time systems. The idea is to formalize the real-time system as a logical conjunction of HOL predicates, whereas each one of these predicates define an autonomous component or process of the given real-time system. The random or unpredictable behavior found in these components is modeled as random variables. This formal specification can then be used in a HOL theorem prover to reason about both functional and performance related properties of the given real-time system. In order to illustrate the practical effectiveness of our approach, we present the analysis of the Stop-and-Wait protocol, which is a classical example of real-time systems. The functional correctness of the protocol is verified by proving that the protocol ensures reliable data transfers. Whereas, the average message delay relation is verified in HOL for the sake of performance analysis. The paper includes the protocol’s formalization details along with the HOL proof sketches for the major theorems

Mixed-Critical Systems Design with Coarse-grained Multi-core Interference

International audienceThose autonomic concurrent systems which are timing-critical and compute intensive need special resource managers in order to ensure adaptation to unexpected situations in terms of compute resources. So-called mixed-criticality managers may be required that adapt system resource usage to critical run-time situations (e.g., overheating, overload, hardware errors) by giving the highly critical subset of system functions priority over low-critical ones in emergency situations. Another challenge comes from the fact that for modern platforms-multi-and many-cores-make the scheduling problem more complicated because of their inherent parallelism and because of "parasitic" interference between the cores due to shared hardware resources (buses, FPU's, DMA's, etc.). In our work-in-progress design flow we provide the so-called concurrency language for expressing, at high abstraction level, new emerging custom resource management policies that can handle these challenges. We compile the application into a representation in this language and combine the result with a resource manager into a joint software design used to deploy the given system on the target platform. In this context, we discuss our work in progress on a scheduler that aims to handle the interference in mixed-critical applications by controlling it at the task level

A Framework for Evaluating Schedulability Analysis Tools

International audienceThere exists a large variety of schedulability analysis tools based on dierent, often incomparable timing models. This variety makes it dicult to choose the best t for analyzing a given real-time system. To help the research community to better evaluate analysis tools and their underlying methods, we are developing a framework which consists of (1) a simple language called RTSpec for specifying real-time systems, (2) a tool chain which translates a system specication in RTSpec into an input for various analysis tools, and (3) a set of benchmarks. Our goal is to enable users and developers of schedulability analysis tools to compare such tools systematically, automatically and rigorously

Schedulability Analysis Using Two Clocks

In classic scheduling theory, real-time tasks are usually assumed to be periodic, i.e. tasks arrive and compute with xed 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

Robustness and Implementability of Timed Automata

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

Modeling of WEST plasmas with reduced Lower-Hybrid model: interplay with transport and parameter optimization

International audienceA heuristic reduced model was developed in METIS [Artaud et al, 2018] for a fast and reliable Lower-Hybrid Heating and Current Drive (LHCD) power and current deposition. Its performance is studied in a stand-alone way through experiments and first-principle modeling comparisons within a WEST database. Its self-consistent evolution is then characterized through an integrated modeling approach incorporating the interplay with transport