Net Topology Exploration and Tuning for Mitigating Congestion in Global Routing

The main task of global routing in the physical design flow assigns nets to specific routing bins in a die with the objective of minimizing the total wirelength of the net routes while satisfying the horizontal and vertical track constraints over the bins. Thus, it is very important to tune the net topologies passing over the congested bins with a minimal increase of wirelength. In this work, we propose an effective net topology exploration and route tuning method to mitigate the routing congestion. Precisely, inspired by an encoding concept, called Rectilinear Edge Sequence (RES), developed in the prior work to compactly and conveniently represent a rectilinear Steiner tree (RST) for each net, we propose a method of systematically and effectively exploring alternative RES encodes for the nets in congested regions so as to find the best suited RSTs for reducing the congestion at a minimal cost of wirelength increase. Through experiments with benchmark circuits, it is shown that our net topology exploration and route tuning method is able to reduce the amount of track overflows by 10.7% with only a 1.7% increase in wirelength when compared to using net topologies of minimal wirelength produced by the state-of-the-art prior work.