Ordered single chain tree a new coding scheme for standard cell placement

Abstract

VLSI standard cell placement is a NP hard problem, which divides into global placement and detail placement phases. In this paper, we proposed a novel coding scheme named ordered single chain tree (OSCT) for detail placement in standard cell placement. Its solution space is n!2n-1 and code length is lgn+(n-1) (where n is the number of cells), which are smaller and shorter than normalized polish expression[3] for standard cell placement. Because of its string structure, OSCT coding scheme can be employed combining with any artificial intelligent algorithms such as simulated annealing (SA) and genetic algorithm (GA) to search for optimal solution in detail placement stage conveniently. This characteristic will enhance the management scale in detail placement, release the workload and uncertainty in global placement, and thus improve whole quality of standard cell placement. Experiments on modified MCNC benchmarks show the effectiveness and efficiency of OSCT coding scheme.