Rewired retiming for free flip-flop reductions without delay penalty

Abstract

Due to the intrinsic difference between fan-in and fan-out counts of a retimed component, the number of flip-flops tends to be undesirably increased in a conventional retiming procedure, which can cause a significant area/power penalty on the retimed circuit. Nonetheless, because of the higher dominance on interconnect delays, without a mechanism to reflect real physical design accurately, the clock period produced by a retiming scheme will be unrealistic. To overcome these two major drawbacks of the conventional retiming technique, we propose a novel retiming flow combined with rewiring, being able to largely cut down flip-flops (FFs) while with the original retimed clock period uncompromised. For a more accurate delay estimation, all interconnect delays are formulated and calculated based on real placements. Experimental results show that this novel rewired retiming scheme can bring a reduction of 18.7% (on average) on the number of flip-flops compared to the original retiming without rewiring. This large FF reduction can be considered a free gain as the retimed clock period can still be kept without compromise in such flow. Further experiments have indicated that about 8.26% of the total dynamic power can be saved.