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Open AccessArticle

Improved Parallel Legalization Schemes for Standard Cell Placement with Obstacles

Computer Science, University of Thessaly, 35131 Lamia, Greece
Informatics and Telecommunications, University of Athens, 106 79 Athens, Greece
Computer Science and Biomedical Informatics, University of Thessaly, 35100 Lamia, Greece
Electrical and Computer Engineering, University of Thessaly, 382 21 Volos, Greece
Author to whom correspondence should be addressed.
This paper is an extended version of our paper published in A Tetris-based Legalization Heuristic for Standard Cell Placement with Obstacles. In Proceedings of the 7th International Conference on Modern Circuits and Systems Technologies (MOCAST 2018), Thessaloniki, Greece, 7–9 May 2018.
Technologies 2019, 7(1), 3;
Received: 9 November 2018 / Revised: 18 December 2018 / Accepted: 19 December 2018 / Published: 22 December 2018
(This article belongs to the Special Issue Modern Circuits and Systems Technologies on Electronics)
PDF [3043 KB, uploaded 22 December 2018]


In standard cell placement, a circuit is given consisting of cells with a standard height, (different widths) and the problem is to place the cells in the standard rows of a chip area so that no overlaps occur and some target function is optimized. The process is usually split into at least two phases. In a first pass, a global placement algorithm distributes the cells across the circuit area, while in the second step, a legalization algorithm aligns the cells to the standard rows of the power grid and alleviates any overlaps. While a few legalization schemes have been proposed in the past for the basic problem formulation, few obstacle-aware extensions exist. Furthermore, they usually provide extreme trade-offs between time performance and optimization efficiency. In this paper, we focus on the legalization step, in the presence of pre-allocated modules acting as obstacles. We extend two known algorithmic approaches, namely Tetris and Abacus, so that they become obstacle-aware. Furthermore, we propose a parallelization scheme to tackle the computational complexity. The experiments illustrate that the proposed parallelization method achieves a good scalability, while it also efficiently prunes the search space resulting in a superlinear speedup. Furthermore, this time performance comes at only a small cost (sometimes even improvement) concerning the typical optimization metrics. View Full-Text
Keywords: standard cell placement; cell legalization; obstacles; Abacus; Tetris; parallelization. standard cell placement; cell legalization; obstacles; Abacus; Tetris; parallelization.

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Oikonomou, P.; Dadaliaris, A.N.; Kolomvatsos, K.; Loukopoulos, T.; Kakarountas, A.; Stamoulis, G.I. Improved Parallel Legalization Schemes for Standard Cell Placement with Obstacles. Technologies 2019, 7, 3.

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