%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.
   "rate\-monotonic" or "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.