Cell Shifting Aware of Wirelength and Congestion

Liu Dawei
Tsinghua University


The technique of cell shifting has the advantage of linearly smoothing the overlap in placement. In the shifting process we should preserve the integrity of the original placement as much as possible and do less damage to the relative locations of the cells. The current cell shifting methods only locally or globally smooth the density without considering the relation between the local and the global density. Furthermore, the cells generally are treated as points with area during cell shifting. In this paper we present a new cell shifting technique called CSAWGC to smooth the density distribution. CSAWC obtains the shifting distance while considering the local and the global density distribution simultaneously. The density and wirelength are taked into consideration while shifting the cells. We also discretize the standard cells and the macro blocks crossing multi-bin, and give the cell shifting distance by summing the shifting vector of the discrete module so as to get a more smooth speed. CSAWC has been embedded into the global placement process of CPlace, experimental result shows that the average runtime and HPWL have reduced 78% and 7% respectively comparing to DPlace.