A comparison of fixed-priority and static cyclic scheduling for distributed automotive control applications

This paper compares different scheduling policies applied to distributed systems intended for automotive real-time control applications. We describe the characteristics of systems using fixed priority (FP) and static cyclic (SC) scheduling of processors and bus communication, with combinations ranging from FP bus-FP processors to SC bus-SC processors. FP bus is represented by the Controller Area Network protocol (CAN) and SC bus by a Time Division Multiple Access (TDMA) protocol. We also study the effects of using a global time base. Our main concern is control performance, including input and output jitter and control delay and therefore the response time of a sequence of control tasks and the related communication. For each system configuration we analyze the expected response times of a series of control related tasks (delay) and the temporal variation of the input and output instants (jitter).