Scheduling the CAN bus with earliest deadline techniques

Controller Area Network (CAN) is widely used in real-time automobile control and is gaining wider acceptance as a standard for factory automation. This paper discusses the applicability of Earliest Deadline (EDF) techniques to the scheduling of CAN messages. Earliest deadline can guarantee higher network utilization than fixed-priority schemes like Deadline or Rate Monotonic (DM, RM), but it is difficult to implement in local area networks or focal buses. The reason is the need for updating the deadlines (priorities) at each scheduling round and the limited numer of priority levels offered by the arbitration protocol. This deadline encoding problem results in an additional priority inversion factor when considering the schedulability analysis of hard real-time messages. This paper describes an effective deadline encoding method and discusses its implementation and its effects on the guarantee analysis. In spite of a limited processor overhead (less than 5% of CPU time) the proposed EDF implementation allows a increase (up to 20%); in the feasible network workload. This trade off will be made more convenient as controller technology evolves.