Routability driven white space allocation for fixed-die standard-cell placement

Abstract

The use of white space in fixed-die standard-cell placement is an effective way to improve routability. In this paper, we present a white space allocation approach that dynamically assigns white space according to the congestion distribution of the placement. In the top-down placement flow, white space is assigned to congested regions using a smooth allocating function. A post allocation optimization step is taken to further improve placement quality. Experimental results show that the proposed allocation approach, combined with a multilevel placement flow, significantly improves placement routability and layout quality.In our experiments, we compared our placement tool with two other fixed-die placers using an industrial place and route flow. Placements created by all three tools have been routed with an industrial router (Warp Route of Cadence). Compared with a leading-edge industrial tool, our placer produces placements with similar or better routability and on average 8.8% shorter routed wirelength. Furthermore, our tool produces placement that runs faster through the Warp Route compared with the industrial tool. Compared with a state-of-the-art academic placement tool (Capo/MetaPlacer), our placer shows ability to produce more routable placements: for 15 out of all 16 benchmarks our placer's outputs are routable while Capo/MetaPlacer only creates 4 routable placements.