Josep Vidal UPVLC jvidal@disca.upv.es Ismael Ripoll UPVLC iripoll@disca.upv.es 2003 OCERA Consortium RTLinux PSignals PTimers Real-Time, POSIX, timers When performing a schedulability test, scheduling analysis relies on a known worst-case execution time (WCET). Nevertheless, estimating WCET is a difficult task due to the different execution paths within a program and today's computer architectures. Without bound on execution time, a task could execute more than estimated, causing other tasks to loose its deadlines. This, on most hard real time application, may result in catastrophic consequences. This component tries to give a solution to this problem, implementing execution time timers within the task scheduler. This kind of timers may be used to detect execution time overruns in the application, and to limit their effects. As an example, if a timer is created using a CPU-Time clock of a particular thread, and a relative expiration time is given, it can be used to notify that a certain budget of execution time has elapsed, for that thread. If the timer is armed each time a thread is activated, and the relative expiration time is set to the thread's estimated worst-case execution time (plus some small amount to take into account the limited resolution and precision of the CPU-Time clock), then the timer will only expire if the thread suffers an execution time overrun.