Unfolding and retiming data-flow DSP programs for RISC multiprocessor scheduling

Retiming and unfolding are two useful techniques which have been effectively applied in many fields. These two techniques are combined to solve the problem of rate-optimal scheduling for unit-time data flow graphs (DFGs). A rate-optimal retimeable graph is a DFG such that after a legal retiming a rate-optimal schedule can be obtained. For the case of unit-time DFG, which is applicable to RISC multiprocessors, the best known upper-bound for an unfolding factor which produces a rate-optimal retimeable DFG is improved, and it is shown that the result is the minimum possible unfolding factor for rate-optimal schedules. Moreover, for any unfolding factor, the corresponding minimum rate is given by a simple criterion. Since it is proved that the order of retiming and unfolding is irrelevant, efficient polynomial-time retiming algorithms are obtained