Redistribute White Space for Minimizing Wire Length

Most existing floorplanning algorithms compact blocks to the left and bottom. Although the compacting obtains an optimal area, it may not be good to meet other objectives such as minimizing total wire length, routing congestion or buffer allocation. In this paper, we study the problem of distributing white space in floorplanning for minimizing total wire length. The problem can be formulated as linear programming. We propose an efficient min-cost flow based approach to solve it. Our approach guarantees to obtain the minimum of total wire length and meanwhile keep the minimum area for a given floorplan representation. We also show that the approach can be easily extended to handle constraints such as fixed-frame (fixed area), boundary pins, pre-placed blocks, boundary blocks, range placement, alignment and abutment, rectilinear blocks, cluster placement, and bounded net delay, without loss of optimality. The algorithm is so efficient in that it finishes in less than 0.4 seconds for all MCNC benchmarks of block placement. It is also very effective. Experimental results show we can further improve 4.2% of wire length even on very compact floorplans. Thus it provides an ideal way of post-floorplanning (refine floorplanning).

By: Xiaoping Tang, Martin D. F. Wong

Published in: RC23323 in 2004


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