Placement: introduction/Problem Formulation
Gi-Joon Nam, Paul G. Villarrubia · Auerbach Publications eBooks · 2008
Placement is a physical synthesis task that transforms a block/gate/transistor-level netlist into an actual layout for timing convergence. The placement problem is usually divided into subproblems—global placement, legalization, and detailed placement—and each sub-problem is attacked separately. The fundamental formulation of the placement problem tends to stay the same, even in the new variants of placement algorithms. Some class of global placement algorithms, such as a partitioning-based algorithms or simulated annealing, is effective in directly handling hyper-edge nets. The intuition of the wirelength based placement objective function is to reduce signal delays of the design and enhance routability simply by minimizing the total. The legalization step then transforms an illegal global placement solution into a legal one while minimizing the perturbation to the original global placement solution. Placement algorithms are typically based on a simulated annealing, top-down cut-based partitioning, or analytical paradigm.