Abax: 2D/3D legaliser supporting look-ahead legalisation and blockage strategies

Abstract

Abax is a modern version of the classical Abacus, minimum displacement, greedy legaliser. Abax supports single-tier 2D or 3D legalisation for multiple, logic-on-logic 3D-IC tiers, efficient look-ahead legalisation of intermediate Global Placement (GP) iterations, Hard Macros, Blockages, row density constraints and multiple local cell displacement functions and cell orderings. For 3D-IC, Abax can produce multi-tier 3D-IC placements by performing Legalisation-based Partitioning. For efficient Look-ahead Legalisation, Abax supports two new local displacement cost functions, multi-cell mean and multi-cell total. We show that the classical single-cell displacement and multi-cell total can result in artifacts when legalising early intermediate GPs, and that multi-cell mean is the best candidate for Look-ahead Legalisation. Obstructions, i.e. Hard Macros and Blockages are handled by using two strategies. We present legalisation results for the ISPD2014 and ISPD2015 benchmarks, by using GP generated from Eh?Placer, and HPWL measurement by using RippleDP. For 3D, two-tier legalisation we illustrate a ∼30% reduction in HPWL for a set of ISPD2014 benchmarks. For 2D legalisation on the ISPD2015 benchmarks, our average HPWL increase over GP is 3.03%, compared to 7.21% of the Eh?Placer legaliser, and 43.16% of the RippleDP legaliser. © 2018 EDAA.