USING PRIORITY INHERITANCE TECHNIQUES TO OVERRIDE THE SIZE LIMIT OF CAN MESSAGES

The CAN bus, highly appreciated for its efficiency and low cost, is widely adopted in many fields, especially where real-time properties are required. However, it is particularly tailored for short data, supporting up to eight data bytes per frame. Larger data entities need to be fragmented so that they can be transferred over the network. Such fragmented messages may experience long delays caused by preemption by higher priority messages, even when these still exhibit slack. This problem has been found in lift control systems in which multi-frame CAN messages had to be sent regularly and were also subject to timing constraints. This paper shows how to use current analysis to deduce response times for multi-frame CAN messages and then it proposes using resource management policies in the CAN bus, namely the Priority Inheritance Protocol, to exploit the slack of higher priority messages and reduce those response times. The paper presents several results that show the efficiency of the proposed mechanisms and highlight their benefits and drawbacks.