Context-sensitive Parametric WCET Analysis

In this paper, we propose aWCET analysis that focuses on two aspects. First, it supports contextsensitive hardware and software timing effects, meaning that it is sensitive to the execution history of the program and thus can account for effects like cache persistence, triangular loop, etc. Second, it supports the introduction of parameters in both the software model (e.g. parametric loop bounds) and the hardware model (e.g. number of cache misses). WCET computation by static analysis is traditionally handled by the Implicit Path Enumeration Technique (IPET), using an Integer Linear Program (ILP) that is difficult to resolve parametrically. We suggest an alternative tree-based approach. We define a context-sensitive CFG format to express these effects, and we provide an efficient method to process it, giving a parametric WCET formula. Experimental results show that this new method is significantly faster and more accurate than existing parametric approaches

Code generation for multi-phase tasks on a multi-core distributed memory platform

International audienceEnsuring temporal predictability of real-time systems on a multi-core platform is difficult, mainly due to hard to predict delays related to shared access to the main memory. Task models where computation phases and communication phases are separated (such as the PRedictable Execution Model), have been proposed to both mitigate these delays and make them easier to analyze. In this paper we present a compilation process, part of the Prelude compiler, that automatically translates a high-level synchronous data-flow system specification into a PREM-compliant C program. By automating the production of the PREM-compliant C code, low-level implementation concerns related to task communications become the responsibility of the compiler, which saves tedious and error-prone development efforts

Minimizing a real-time task set through Task Clustering

International audienceIn the industry, real-time systems are specified as a set of hundreds of functionalities with timing constraints. Implementing those functionalities as threads in a one-to-one relation is not realistic due to the overhead caused by the large number of threads. In this paper, we present task clustering, which aims at minimizing the number of threads while preserving the schedulability. We prove that our clustering problem is NP-Hard and describe a heuristic to tackle it. Our approach has been applied to fixed-task or fixed-job priority based scheduling policies as Deadline Monotonic (DM) or Earliest Deadline First (EDF)

Ordonnancement de tâches périodiques avec précédences étendues sans sémaphores

National audienceCe travail porte sur l'ordonnancement de systèmes embarqués critiques. Ces systèmes sont multi-périodiques et soumis à des contraintes d'échéances. L'implémentation d'un tel système doit de plus être fonctionnellement déterministe (les mêmes sorties produites pour les mêmes entrées), ce qui nécessite de contrôler précisément l'ordre des communications entre tâches, à l'aide de contraintes de précédence. Nous nous intéressons donc à l'ordonnancement de tâches périodiques reliées par des contraintes de précédence étendues (entre tâches de périodes différentes), à l'aide de politiques basées sur les priorités. En raison du caractère critique des applications considérées, on s'intéresse à des politiques d'ordonancement sans sémaphores, afin d'éliminer tout risque d'anomalie d'ordonnancement (un système prouvé ordonnançable avant l'exécution sur la base des WCET devenant non-ordonnaçable à l'exécution en raison d'une tâche ne prenant pas son WCET). Nous proposons une politique d'ordonnancement optimale pour le problème présenté ci-dessus, en priorité dynamique

Implementing Multi-Periodic Critical Systems: from Design to Code Generation

This article presents a complete scheme for the development of Critical Embedded Systems with Multiple Real-Time Constraints. The system is programmed with a language that extends the synchronous approach with high-level real-time primitives. It enables to assemble in a modular and hierarchical manner several locally mono-periodic synchronous systems into a globally multi-periodic synchronous system. It also allows to specify flow latency constraints. A program is translated into a set of real-time tasks. The generated code (\C\ code) can be executed on a simple real-time platform with a dynamic-priority scheduler (EDF). The compilation process (each algorithm of the process, not the compiler itself) is formally proved correct, meaning that the generated code respects the real-time semantics of the original program (respect of periods, deadlines, release dates and precedences) as well as its functional semantics (respect of variable consumption).Comment: 15 pages, published in Workshop on Formal Methods for Aerospace (FMA'09), part of Formal Methods Week 2009

Automated runnable to task mapping

We propose in this paper, a method to automatically map runnables (blocks of code with dedicated functionality) with real-time constraints to tasks (or threads). We aim at reducing the number of tasks runnables are mapped to, while preserving the schedulability of the initial system. We consider independent tasks running on a single processor. Our approach has been applied with fixed-task or fixed-job priorities assigned in a Deadline Monotonic (DM) or a Earliest Deadline First (EDF) manner

Palmer-Chalker correlations in the XY pyrochlore antiferromagnet Er2Sn2O7

\ersn\, is considered, together with \erti, as a realization of the XY antiferromagnet on the pyrochlore lattice. We present magnetization measurements confirming that \ersn\, does not order down to 100 mK but exhibits a freezing below 200 mK. Our neutron scattering experiments evidence the strong XY character of the \er moment and point out the existence of short range correlations in which the magnetic moments are in peculiar configurations, the Palmer-Chalker states, predicted theoretically for an XY pyrochlore antiferromagnet with dipolar interactions. Our estimation of the \ersn\, parameters confirm the role of the latter interactions on top of relatively weak and isotropic exchange couplings

Dynamic Priority Scheduling of Periodic Tasks with Extended Precedences

International audienceThe software architecture of a critical embedded control system generally consists of a set of multi-periodic communicating tasks. In order to be able to describe such a system, we define the notion of \emph{semaphore precedence constraint}, which supports multi-rate communications that follow regular repetitive patterns. We propose a feasibility test for EDF and we study three implementations, for periodic task sets related by such extended precedences on monoprocessor architectures