Optimal cell flipping in placement and floorplanning

In a placed circuit, there are a lot of movable cells that can be flipped to further reduce the total wirelength, without affecting the original placement solution. We aim at solving this flipping problem optimally. However, solving such a problem optimally is non-trivial given the gigantic sizes of modern circuits. We are able to identify a large portion of cells (about 75%) of which the orientation (flipped or not flipped) can be determined independent of the orientations of all the other cells. We have derived three non-trivial conditions to identify those so called independent cells, strictly solvable cells and conditionally solvable cells. In this way, we can greatly reduce the number of cells whose orientations are dependent on each other. Finally, the cell flipping problem of the remaining dependent cells can be formulated as a Mixed Integer Linear Programming (MILP) problem and solved optimally. However, this may still be too slow for extremely large circuits and we have appli...

• Type: Conference
• Year: 2006
• Where: DAC
• Authors: Chiu-Wing Sham, Evangeline F. Y. Young, Chris C. N. Chu
• Keywords: DAC 2006, Design Automation, Flipping Problem, Integer Linear Programming, Solvable Cells