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 smooth allocating functions. 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. A set of approaches for white space allocation has been presented and compared in this paper. All of them are based on routability-driven methods. However, these approaches vary in the allocation function and allocation aggressiveness. All the placement results are investigated by feeding them into a widely used industrial router (Warp Route of Cadence). Comparisons have been made between: 1) placement with or without white space allocation; 2) different white space allocation approaches; and 3) our placement flow, industrial placement tool, and the other state-of-the-art academic placement tool.