Leakage efficient chip-level dual-Vdd assignment with time slack allocation for FPGA power reduction

To reduce power, Vdd programmability has been proposed recently to select Vdd-level for interconnects and to power-gate unused interconnects. However, Vdd-level converters used in the Vdd-programmable method consume a large amount of leakage. In this paper, we develop chip-level dual-Vdd assignment algorithms to guarantee that no low-Vdd interconnect switch drives high-Vdd interconnect switches. This removes the need of Vdd-level converters and reduces interconnect leakage and interconnect device area by 91.78% and 25.48%, respectively. The assignment algorithms include power sensitivity based heuristics with implicit time slack allocation and a linear programming (LP) based method with explicit time slack allocation. Both first allocate time slack to interconnects with higher transition density and assign low-Vdd to them for more power reduction. Compared to the aforementioned Vdd-programmable method using Vdd-level converters, the LP based algorithm reduces interconnect power by 65.13% without performance loss for the MCNC benchmark circuits. Compared to the LP based algorithm, the sensitivity based heuristics can obtain slightly smaller power reduction but run 4× faster.