Dynamic Priority Based Message Scheduling on Controller Area Network

Controller area network (CAN) is a serial communication protocol developed in early 1980's by Robert Bosch. Low cost, ease of use and ability to work in harsh EMI environments have resulted in its widespread acceptance in automotive and automation industry. Message scheduling and access to the bus in CAN is performed through a fixed Message Identifier field, which is also the basis for a static priority. Although this fixed priority apparently results in good bus utilization but low priority messages may suffer from starvation due to an ill designed message identifier allocation scheme. Also with its introduction into newer fields, the fixed priority per message is looking to be a limitation for some applications. Un till now there has been no work to add this faculty to CAN in a standardize way. This paper presents a set of algorithms and guide lines to support the dynamically changing priorities in a CAN network without breaking the integration with existing CAN based networks. The scheme is effectively a generalization of the single priority per message to a multi-priority-window per message.