Ripple: A Robust and Effective Routability-Driven Placer

The significant mismatch between the objective of wirelength and routing congestion makes the routability issue even more important in placement. In this paper, we describe a routability-driven placer called Ripple. Each step, including global placement, legalization, and detailed placement, is made to trade-off between routability and wirelength. We propose a robust and effective flow by using cell inflation to relieve routing congestion. Cell inflation has traditionally been used to deal with congestion and we will discuss how this technique can be used easily and robustly in the global placement. Besides, unlike many previous works that focus on different types of swapping strategies, we analyze and propose some simple and effective approaches when considering routability in the legalization and detailed placement steps. Experimental results show that Ripple is particularly effective in improving routability. When compared to the top results in the ISPD 2011 Contest and SimPLR, Ripple can obtain the smallest overflow and half-perimeter wirelength on average, while the congestion hot spots are also distributed sparsely in Ripple.