Meeting Real-Time Constraints in CAN

Abstract

This paper deals with the problem of information flow scheduling in a communication system based on CAN ISO IS-11898 physical medium access mechanism. It mainly features a bus access arbitration protocol based on a priority assigned to each message to be transmitted; if two or more messages are transmitted at the same time by different communication nodes, only the message with the highest priority continues to be transmitted, the other being stopped. In real-time applications, messages are relevant to process variables which must be transmitted within strict time constraints; according to the CAN ISO IS-11898 bus arbitration protocol, respect of real-time constraints depends on the priority assigned to each variable. The aim of the paper is to propose a procedure for dynamic assignment of priorities to variables to be transmitted, in such a way the relevant real-time requirements are fulfilled. Although many other approaches can be found in literature, the proposal is original as it is based on standard full CAN communication stacks.