Worst - Case Timing Analysis of the Rtems Real - Time Operating System Antoine Colin , Isabelle Puaut

Knowing tasks worst-case execution times (WCET) is crucial in systems with hard real-time constraints, in which missing a deadline can have catastrophic consequences. Worst-case execution time analysis (WCET analysis), thanks to the analysis of a piece of code, returns an upper bound for the time required to execute it on a given hardware. Since real-time operating systems are used in many systems with hard real-time constraints, it is crucial that the WCET of the application tasks integrate the WCET of the system calls included in their code. This paper reports the results of a study aiming at using WCET analysis in order to obtain the WCET of the system calls of the RTEMS real-time kernel. The main result of our study is that it is possible to use WCET analysis to obtain the worst-case execution times of a real-time kernel. In addition, we highlight the problems encountered during the study. The goal is to provide the users of WCET analysis tools with the information regarding the problems that are likely to be found with the code of real-time operating systems, and to provide the designers of WCET analysis tools with guidance regarding the tools that are best suited to the analysis of real-time operating systems. Irisa Analyse du temps d'ex ecution au pire cas du syst eme d'exploitation temps-r eel RTEMS R esum e : Dans le domaine des syst emes temps-r eel dur, la connaissance des temps d'ex ecution au pire cas (WCET, pour worst-case execution time) des t^ aches est cruciale. En eeet, dans ces syst emes le d epassement d'une ech eance temporelle peut avoir des cons equences catastrophiques. L'analyse de temps d'ex ecution au pire cas (analyse de WCET) a pour but de fournir une borne sup erieure au temps d'ex ecution d'un programme sur un mat eriel donn e, par analyse statique de son code. Dans le cas d'un syst eme temps-r eel dur qui repose sur un syst eme d'exploitation temps-r eel, les WCET des t^ aches applicatives doivent int egrer le WCET des appels de syst eme qu'elles contiennent. Cet article pr esente les r esultats d'une etude visant a appliquer l'analyse de WCET aan d'obtenir le WCET des appels du noyau temps-r eel RTEMS. Le r esultat principal de notre etude est la possibilit e d'utiliser l'analyse de WCET pour obtenir les temps d'ex ecution au pire cas d'un noyau temps-r eel. …