Chapter 28: Buffering in the Layout Environment

Chapters 26 and 27 presented buffering algorithms where the buffering problem was isolated from the general problem of timing closure. The main problem with this extraction is that there are not necessarily resources available to put the buffers or wires in their desired locations. One way to manage this flow is to put the buffers in their ideal locations and allow a legalization procedure to move them to actual locations. The problem with this approach is that buffers may be moved quite far from their ideal locations, which could completely corrupt the quality of the solution. It is much better to place the buffers in regions where appear to be sufficient space, so that legalization would move the buffers by at most 10-20 routing tracks, which would preserve the original solution. To do this, one must certainly take into account the blockages and preferably local placement and routing congestion. In this chapter, we explore techniques which consider these factors.