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Adding local priority-based dispatching mechanisms to P-NET networks: a fixed priority approach
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Resumo(s)
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 prioritybased
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.
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IEEE