Delay Analysis of Priority Promotion Systems

Distributed real-time systems are often characterised by tight timing requirement on data exchanges, which should take place within precise deadlines in order to ensure that the system operates correctly. In this paper, a new priority promotion mechanism is introduced which is based on the medium access technique of the Controller Area Network (CAN) protocol and which offers a higher degree of robustness and responsiveness than token-based networks. At the same time, unlike conventional CAN networks, the one proposed is very fair and provides a means by which the schedule for the different real-time message streams in the system can be defined precisely. The priority promotion mechanism is analysed in detail and an analytical expression for an upper bound on the worst case transmission time is found.