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Reducing pessimism in CAN response time analysis
Publication Type:
Report - MRTC
ISRN:
MDH-MRTC-51/2002-1-SE
Abstract
This paper investigates the level of pessimism in the traditional
schedulability analysis for the Controller Area Network (CAN).
Specifically, we investigate the effects of considering bit-stuffing
distributions instead of worst case bit-stuffing. This allows us to
obtain bus utilisation values more close to reality. On the other
hand, since our analysis is based on assumptions concerning
distributions of stuff-bits, our response times will only be met
with some probability.We introduce a model and some methods, that relax the pessimism of the
worst case analysis, and we show the effect of our methods by
considering both an artificial traffic model and samples of real CAN
traffic. Also, we propose a simple coding scheme that substantially
reduces the number of stuff-bits in the considered real traffic.Delay variations (jitter) in computations and communications cause
degradation of performance in control applications. There are many
sources of jitter, including variations in execution time and bus
contention. By introducing some restrictions when using CAN, such as a
small reduction of available frame priorities, we are able to reduce
the number of stuff-bits in the worst case. We also combine this with
the methods mentioned above that reduces the number of stuff-bits in
the data part of the frame. We show the actual penalty introduced by
forbidding priorities and we show the overall improvement by using
these techniques together in a small case study.
Bibtex
@techreport{Nolte322,
author = {Thomas Nolte},
title = {Reducing pessimism in CAN response time analysis},
number = {ISSN 1404-3041 ISRN MDH-MRTC-51/2002-1-SE},
month = {March},
year = {2002},
url = {http://www.es.mdu.se/publications/322-}
}