Message Packing Algorithm for CAN-Based Legacy Control Systems Mixed with CAN and FlexRay

Hard real-time systems such as automotive control systems have to guarantee that strict deadlines are met for applications. Recent automotive control systems have been network systems that have combined event-triggered with time-triggered networks, i.e., Controller Area Network (CAN) and FlexRay. A CAN-FlexRay gateway has to execute real-time message transfers from CAN to FlexRay and from FlexRay to CAN to guarantee that communication deadlines are met. Most gateways in the automotive control systems select messages according to the priority of the messages and pack them into frames. However, when many events of same kinds occur within the short period, the gateway cannot guarantee that communication deadlines for time-triggered and first event-triggered messages will be met because many event-triggered messages prevent time-triggered messages from being packed into frame. This paper describes a novel real-time message packing algorithm that prioritizes transmissions of time-triggered messages and first event-triggered messages to guarantee that communication deadlines for them are met. The message packing algorithm statically establishes various clusters of both communication messages and FlexRay frames and preferentially packs a message into a specified frame according to relationship between clusters of them. We evaluated the proposed message packing algorithm by developing a communication middleware with the algorithm for CAN-based legacy control systems and a CAN-FlexRay gateway including the middleware and found that the algorithm guarantees communication deadlines for time-triggered messages and first event-triggered messages are met in spite of packing into fewer FlexRay frames by establishing the cluster which is defined to pack their messages certainly.