Voltage island-driven floorplanning

Energy efficiency has become one of the most important issues to be addressed in today\´s system-on-a-chip (SoC) designs. One way to lower the power consumption is to reduce the supply voltage. Multi-supply voltage (MSV) is thus introduced to provide higher flexibility in controlling the power and performance trade-off. In region-based MSV, circuits are partitioned into "voltage islands" where each island occupies a contiguous physical space and operates at one supply voltage. These tasks of island partitioning and voltage level assignments should be done simultaneously in the floorplanning process in order to take those important physical information into consideration. In this paper, we consider this core-based voltage island driven floorplanning problem including islands with power down mode, and propose a method to solve it. Given a candidate floorplan solution represented by a normalized Polish expression, we are able to obtain optimal voltage assignment and island partitioning (including islands with power down mode) simultaneously to minimize the total power consumption. Simulated annealing is used as the basic searching engine. By using this approach, we can achieve significant power savings (up to 50%) for all data sets, without any significant increase in area and wire length. Our floorplanner can also be extended to minimize the number of level shifters between different voltage islands and to simplify the power routing step by placing the islands in proximity to the corresponding power pins.