Experimental study of message latencies on FlexRay bus

Abstract: FlexRay is a real-time communication protocol for automotive networks which was developed by a consortium of over hundred automotive companies. A communication cycle in FlexRay consists of an event driven segment known as dynamic segment. we have studied the delays suffered by messages that are transmitted in the dynamic segment of FlexRay. To obtain this goal we have used FlexRay nodes that were connected on a bus topology. We have various messages with same payloads and different transmission intervals. While transmitting we have stamped the frame with message instance counter, cycle number and message ID. On the receiving side, we have stamped each received message with current cycle number in order to get delay. Transmission delays are measured in terms communication cycles which are obtained by taking the difference of transmitting cycle and receiving cycle.Experimental results obtained showed that higher priority messages are delayed maximum by one cycle if they are placed in transmission buffer when their slot has passed. Whereas low priority message suffer delays or they might not sent at all if high priority messages have smaller transmission periods as compare to low priority messages.