Temporal robustness of real-time architectures specified by estimated wcets

Abstract — Real-time dimensioning depends on the Worst Case Execution Time (WCET) of its tasks. Using estimated WCETs for the dimensioning is less conservative but execution overruns are more likely to happen. Fault tolerant mechanisms must be implemented to preserve the real-time system from timing failures, associated to late task termination deadlines misses, in the case of WCETs overruns. We show in this article how to compute the extra duration (allowance) on the WCETs that can be given to faulty tasks while still preserving all the deadline constraints of the tasks. This allowance is used on-line to tolerate WCET overruns. We present a mechanism called the Latest Execution Time (LET) using the allowance of the tasks for the temporal robustness of real-time systems. This mechanism only requires classical timers. Its benefits are presented in the context of a java virtual machine meeting the Real-Time Specification for Java (RTSJ) with estimated WCETs. Real-time System; fault tolerance; estimated WCET; allowance; slack time; temporal robustness I