Adding Local Priority-Based Dispatching Mechanisms to P-NET Networks: a Fixed Priority Approach Outdated
Ref: HURRAY-TR-9822 Publication Date: 1, Dec, 1998
Adding Local Priority-Based Dispatching Mechanisms to P-NET Networks: a Fixed Priority ApproachRef: HURRAY-TR-9822 Publication Date: 1, Dec, 1998
In this paper we address the real-time capabilities of P-NET, which is a multi-master fieldbus standard based on a virtual token passing scheme. We show how P-NET’s medium access control (MAC) protocol is able to guarantee a bounded access time to message requests. We then propose a model for implementing fixed priority-based dispatching mechanisms at each master’s application level. In this way, we diminish the impact of the first-come-first-served (FCFS) policy that P-NET uses at the data link layer. The proposed model rises several issues well known within the real-time systems community: message release jitter; pre-run-time schedulability analysis in non pre-emptive contexts; non-independence of tasks at the application level. We identify these issues in the proposed model and show how results available for priority-based task dispatching can be adapted to encompass priority-based message dispatching in P-NET networks.
Notes: This technical report was later updated by HURRAY-TR-9907
11th IEEE Euromicro Conference on Real-Time Systems