The WorldFIP protocol is one of the three profiles that constitute the European fieldbus standard EN-50170. It is particularly well suited to be used in distributed computer-controlled systems (DCCS) where a set of process variables must be shared among network devices. To cope with the real-time requirements of such systems, the protocol provides communication services based on the exchange of identified variables. These exchanges can be periodic or aperiodic. The periodic exchanges have the highest priority and are executed at run-time according to a cyclic schedule. Therefore, the schedulability of periodic exchanges can be determined at pre-run-time when building the schedule table. Concerning the aperiodic exchanges, the situation is different, since aperiodic requests have lower priority and are handled according to a FCFS policy. In this paper a response time-based schedulability analysis for the real-time traffic is presented. Such analysis considers both types of traffic in an integrated way according to their priorities. Furthermore, a fixed-priorities based policy is also used to schedule the periodic traffic. The analysis represents an improvement relatively to previous work and it incurs in a sufficiently low run-time overhead so that it can be evaluated on-line. This particular feature is of particular importance when a planning scheduler is used instead of the typical off-line static scheduler to allow on-line changes to the set of periodic process variables.
Published in IEEE Transactions on Industrial Electronics, IEEE, Edited: J.
Rodriguez, Volume 49, Issue 5, pp 1165-1174.