Time-Triggered Scheduling of Mixed-Criticality Systems

Abstract

Real-time and embedded systems are moving from the traditional design paradigm to integration of multiple functionalities onto a single computing platform. Some of the functionalities are safety critical and subject to certification. The rest of the functionalities are nonsafety critical and do not need to be certified. Designing efficient scheduling algorithms which can be used to meet the certification requirement is challenging. Our research considers the time-triggered approach to scheduling of mixed-criticality jobs with two criticality levels. The first proposed algorithm for the time-triggered approach is based on the OCBP scheduling algorithm which finds a fixed-priority order of jobs. Based on this priority order, the existing algorithm constructs two scheduling tables S LO oc and S HI oc . The scheduler uses these tables to find a scheduling strategy. Another time-triggered algorithm called MCEDF was proposed as an improvement over the OCBP-based algorithm. Here we propose an algorithm which directly constructs two scheduling tables without using a priority order. Furthermore, we show that our algorithm schedules a strict superset of instances which can be scheduled by the OCBP-based algorithm as well as by MCEDF. We show that our algorithm outperforms both the OCBP-based algorithm and MCEDF in terms of the number of instances scheduled in a randomly generated set of instances. We generalize our algorithm for jobs with m criticality levels. Subsequently, we extend our algorithm to find scheduling tables for periodic and dependent jobs. Finally, we show that our algorithm is also applicable to mixed-criticality synchronous programs upon uniprocessor platforms and schedules a bigger set of instances than the existing algorithm.