THE ORDERED-TRANSACTIONS STRATEGY
The self-timed scheduling strategy described in Chapter 5 introduces synchronization checks when processors communicate; such checks permit variations in actor execution times, but they also imply run-time synchronization and arbitration costs. In this chapter we present a scheduling model called orderedtransactions that alleviates some of these costs, and in doing so, trades off some of the run-time flexibility afforded by the self-timed approach. The orderedtransactions strategy was first proposed by Bier, Lee, and Sriram [LB90][BSL90]. In this chapter, we describe the idea behind the ordered-transactions approach and then we discuss the design and hardware implementation of a shared-bus multiprocessor that makes use of this strategy to achieve a low-cost interprocessor communication using simple hardware. The software environment for this board, for application specification, scheduling, and object code generation for the DSP processors is provided by the Ptolemy system developed at the University of California at Berkeley [BHLM94][Pto98].