Schedulability analysis for CAN bus messages  of periodically-varying size

Hussain, Ishfaq; Souto, Pedro; Bletsas, Konstantinos; Awan, Muhammad Ali; Tovar, Eduardo

http://hdl.handle.net/10400.22/21218

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Authors

Hussain, Ishfaq

Souto, Pedro

Bletsas, Konstantinos

Awan, Muhammad Ali

Tovar, Eduardo

Abstract(s)

Conventional CAN bus schedulability analysis assumes that all messages with a given identifier have the same worst-case length. In this paper we extend that analysis to a more general model in which messages with a given identifier may have different lengths, that vary according to a known periodic pattern.That is, for some positive integer S, we assume that the length of message instances n and n + S with the same id is the same. By leveraging such patterns, where present, our new analysis allows for a more efficient use of CAN bus bandwidth than the application of conventional analysis, which can be pessimistic. This may be interesting when a given node sends the values of multiple signals with different periods. In such a scenario, the conventional CAN schedulability analysis would require either the use of different ids for different signals (assuming there are enough of them), which leads to a higher bandwidth overhead because of the reduplication of message headers, or using only one id, but pessimistically always assuming the maximum possible length of the message, for safety reasons.