GPCS: Global placement based on cell spreading method

As a key phase of force-directed placement, cell spreading can smooth the overlap linearly by adding additional forces to shift cells to the suitable place based on the utilization of bins. However, the magnitude and direction of these additional forces is hard to be determined. Unreasonable additional forces will bring great damage to the wire length and run time. In this paper, we present a new fast and accurate global placement called GPCS to cope with these problems and further optimize wire length. It mainly takes the following measures: Firstly, cross net model was used in the initial placement, which will increase the convergent speed and decrease half time in the initial phrase consequently. Secondly, in the process of cell spreading, a coarse half-split strategy is adopted, and with the help of non-scale spreading it will accelerate the quality of the global placement. Thirdly, cells are grouped into three steady sets according to their attributes, external connections and last move, and the different strategies of amending original force are adopted base on the sets respectively, which makes the average wire length reduced by 9.4.