Incremental placement for timing and routability optimization

Abstract

Incremental placement takes an initial placement and modifies the placement to achieve de- sign closure. We address two key problems in incremental placement, timing- and routability- driven placements. First, an incremental timing-driven placement algorithm is presented. It optimizes timing critical paths through a blockage-aware path smoothing. The gates on criti- cal paths are relocated to free spaces around smoothed paths, so legalization is not necessary, while incremental static timing analysis is involved to accurately assess timing changes due to the relocation. Next, we propose an algorithm for timing-driven unified latch placement and cloning. Given a latch and the locations of the fanin and fanout gates, it relocates the latch based on a linear delay model such that the slack is maximized. The latch can be cloned into multiple latches to further improve the slack

each of the replicated latches drives a subset of the fanouts of the original latch. Finally, an incremental placement for pin-accessibility op- timization is presented. We propose two inaccessibility measures of pins which can identify the hard-to-access pins in a cell as well as in a placement. Its application to the placement optimization for improving accessibility of each cell is then presented.