%T Multi\-priority scheduling for transputer\-based real\-time control
%A Peter H. Welch
%E Hussein S. M. Zedan
%B OUG\-13: Real\-Time Systems with Transputers
%X A major requirement of real\-time control applications is a
set of cyclic processes — one for each
"control\-law". Each process must be
managed so that it completes each cycle within a fixed time.
The rate at which each process cycles will be constant, but
will generally be different for different processes.Current
transputer hardware provides very fast pre\-emptive
scheduling for two static priority levels, with
"round\-robin" management within each
level. This is not sufficient to manage securely more than
one such control\-law per transputer — even at very low
processor loadings. Efficient classical solutions (e.g.
"deadline" scheduling) require multiple
and time\-varying priorities.This paper shows how to
implement such solutions simply, and with an acceptable
level of overhead, on the existing (and future) generation
of transputer. Other promising scheduling methods are
discussed. All solutions are expressed in occam with no
assembler inserts and no security rules violated — the
intended applications are safety\-critical! Real performance
figures are reported.Finally, a method of proving (or
dis\-proving) the security of any particular set of process
loadings, operating under any particular scheduling
algorithm, is described.
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