Message scheduling and timing analysis for flexray dynamic segment by considering slot-multiplexing

Abstract

FlexRay is a communication protocol that combines event- and time-triggered communication to increase the schedulability and flexibility of message scheduling in current car systems. Because safety and reliability are particularly crucial for automotive systems, the worst-case response times of signals transmitted by electronic control units must be under their deadlines. To increase the bandwidth utilization, the slotmultiplexing (SM) mechanism that is allowable in protocol specification was adopted to schedule messages offline in the dynamic segment of the FlexRay protocol, and this mechanism was also considered in the timing analysis. The proposed method was feasible to calculate worst-case response time of message under any bus load when considered slot-multiplexing. Then the approach was applied to a Society of Automotive Engineers benchmark to ensure that all messages were schedulable. The simulation results revealed that by using slot-multiplexing, only 17 identifiers were used, which was less than 23 identifiers that were needed when the slot-multiplexing was not considered. It also improved the schedulability of dynamic segment with up to 27% improvement in bus bandwidth utilization.