ABSTRACT
This chapter presents work on space management, legalization, and detailed placement, the design flow steps normally falling between global placement and the start of routing. Fixed-die routing dominates the industry, but faces the problem of routing failure. Space management is also an effective way of adjusting to changes resulting from gate sizing or buffer insertion. Flow-based improvements are sometimes referred to as ripple moves; one can see chains of regions, where logic elements move in sequence through, from dense regions to sparse. A physics-based model can be used to compute particle velocities between bins with different pressures. Many groups have experimented with different legalizers, window sizes for reordering, methods to perform space allocation, and so forth. The placement examples with known optimal benchmarks contain no pads; thus, there are multiple optimal configurations, corresponding to mirroring or flipping of the design.
