Robust priority assignment for messages on Controller Area Network (CAN)

This paper addresses the problem of determining the most robust priority assignment for CAN messages that are subject to transmission errors due to Electromagnetic Interference. In the presence of errors on the bus, CAN messages have a non-zero probability of missing their deadlines. An appropriate choice of priority ordering can minimise the overall worst-case deadline failure probability resulting in a more robust system. This paper shows that "deadline minus jitter" monotonic priority assignment, commonly used for priority assignment in commercial CAN systems, does not always result in the most robust priority ordering. A Robust Priority Assignment algorithm is presented that computes the most robust priority ordering for CAN messages subject to bit errors on the bus. This algorithm is optimal in the sense that it can be used to (i) maximise the number of errors tolerated, (ii) maximise the delay tolerated by any message, or (iii) minimise the probability of any message failing to meet its deadline. This algorithm is efficient and appropriate for use in an engineering context.