Prevention of Sequential Message Loss in CAN Systems

More and more advanced features such as adaptive cruise control, collision avoidance, and stability control are being implemented in vehicles. These features are usually implemented as distributed CAN (controller area network) systems right now. In a CAN system, normally there is no clock synchronization among the ECU (electronic control unit) nodes connected by the CAN bus. Without synchronization, the clocks of those ECU nodes could drift away from each other. A typical clock drift rate of 30 ppm (parts per million) could cause a clock to drift by 108 milliseconds in one hour. The clock drift this large could cause problems in those advanced vehicle control systems. In fact, a sequence of messages could get lost in a distributed CAN system due to the combination of clock drift, transmission jitter, and finite buffer size. To solve the above problem, instead of performing high overhead clock synchronization in the CAN system, this paper provides an economical solution for the prevention of the above message loss problem. The idea is to synchronize the task activations on different ECU nodes and such synchronizations are performed only when necessary. An analysis method is developed for the determination of the synchronization frequency; and an algorithm is provided for the task activation synchronization.