Measurement of Cache-Related Preemption Delay for Spacecraft Computers

Cheol Hea Koo, Hyungshin Kim

Abstract: In order to guarantee task schedulability in real-time embedded systems, analysis on cache and cache behavior at task preemption is required because cache misses cause unpredictable delays in task execution time. Nevertheless, studies on cache behavior and its effects in preemptive multitasking systems have been conducted mainly with simulation and analytic methods, which may induce pessimistic scheduling policy. In this paper, we propose a measurement framework to diagnose the cache-related preemption delay (CRPD) on LEON3 SPARC V8 processor to understand its effect with execution time analysis. The experimental results from several benchmark program execution on the framework show that the time delay and penalty for cache operations are not constant. We were able to identify that each software has a unique degree of cache susceptibility with regard to CRPD. We conclude that this experiment data can be used to prevent real-time tasks from missing the deadline, which is not tolerable in real-time constraints of spacecraft computers, by applying it on real-time scheduling. The results may be useful to the susceptibility analysis of real-time embedded software. The measured CRPD on a specified real target processor can be used to assess the schedulability of task sets to bound WCET on task preemption condition.