Rephasing: A Transformation Technique for the Manipulation of Timing Constraints

We introduce a transformation, named rephasing, that manipulates the timing parameters in control-dataflow graphs. Traditionally high-level synthesis systems for DSP have either assumed that all the relative times, called phases, when corresponding samples are available at input and delay nodes are zero or have automatically assigned values to as part of the scheduling step when software pipelining is simultaneously applied. Rephasing, however, manipulates the values of these phases as a transformation before the scheduling. The advantage of this approach is that phases can be chosen to optimize the algorithm for metrics such as area and power. Moreover, rephasing can be combined with other transformations. We have developed techniques for using rephasing to optimize several design metrics. The experimental results show significant improvements.