On The Engineering of a Stable Force-Directed Placer

Analytic and force-directed placement methods that simultaneously minimize wire length and spread cells are receiving renewed attention from both academia and industry. However, these methods are by no means trivial to implement---to date, published works have failed to provide sufficient engineering details to replicate results. This dissertation addresses the implementation of a generic force-directed placer entitled FDP. Specifically, this thesis provides (1) a description of efficient force computation for spreading cells, (2) an illustration of numerical instability in this method and a means to avoid the instability, (3) metrics for measuring cell distribution throughout the placement area, and (4) a complementary technique that aids in minimizing wire length. FDP is compared to Kraftwerk and other leading academic tools including Capo, Dragon, and mPG for both standard cell and mixed-size circuits. Wire lengths produced by FDP are found to be, on average, up to 9% and 3% better than Kraftwerk and Capo, respectively. All told, this thesis confirms the validity and applicability of the approach, and provides clarifying details of the intricacies surrounding the implementation of a force-directed global placer

On the Use of Directed Moves for Placement in VLSI CAD

Search-based placement methods have long been used for placing integrated circuits targeting the field programmable gate array (FPGA) and standard cell design styles. Such methods offer the potential for high-quality solutions but often come at the cost of long run-times compared to alternative methods. This dissertation examines strategies for enhancing local search heuristics---and in particular, simulated annealing---through the application of directed moves. These moves help to guide a search-based optimizer by focusing efforts on states which are most likely to yield productive improvement, effectively pruning the size of the search space. The engineering theory and implementation details of directed moves are discussed in the context of both field programmable gate array and standard cell designs. This work explores the ways in which such moves can be used to improve the quality of FPGA placements, improve the robustness of floorplan repair and legalization methods for mixed-size standard cell designs, and enhance the quality of detailed placement for standard cell circuits. The analysis presented herein confirms the validity and efficacy of directed moves, and supports the use of such heuristics within various optimization frameworks

On The Engineering of a Stable Force-Directed Placer

I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. ii Analytic and force-directed placement methods that simultaneously minimize wire length and spread cells are receiving renewed attention from both academia and industry. However, these methods are by no means trivial to implement—to date, published works have failed to provide sufficient engineering details to replicate results. This dissertation addresses the implementation of a generic force-directed placer entitled FDP. Specifically, this thesis provides (1) a description of efficient force computation for spreading cells, (2) an illustration of numerical instability in this method and a means to avoid the instability, (3) metrics for measuring cell distribution throughout the placement area, and (4) a complementary technique that aids in minimizing wire length. FDP is compared to Kraftwerk and other leading academic tools including Capo, Dragon, and mPG for both standard cell and mixed-size circuits

Engineering details of a stable force-directed placer

Analytic placement methods that simultaneously minimize wire length and spread cells are receiving renewed attention from both academia and industry. In this paper, we describe the implementation details of a force-directed placer, FDP. Specifically, we provide (1) a description of efficient force computation for spreading cells, (2) an illustration of numerical instability in these methods and a means by which these instabilities are avoided, (3) spread metrics for measuring cell distribution throughout the placement region and (4) a complementary technique which aids in directly minimizing HPWL. We present results comparing our analytic placer to other academic tools for both standard cell and mixed-size designs. Compared to Kraftwerk and Capo 8.7, our tool produces results with an average improvement of 9 % and 3%, respectively