GRIP: Scalable 3D global routing using Integer Programming

We propose GRIP, a scalable global routing technique via integer programming (IP). GRIP optimizes wirelength and via cost without going through a layer assignment phase. GRIP selects the route for each net from a set of candidate routes that are generated based on an estimate of congestion generated by a linear programming pricing phase. To achieve scalability, the original IP is decomposed into smaller ones corresponding to balanced rectangular subregions on the chip. We introduce the concept of a floating terminal for a net, which allows flexibility to route long nets going through multiple subregions. We also use the IP to plan the routing of long nets, detouring them from congested subregions. For ISPD 2007 benchmarks, we obtain 3.9% and 11.3% average improvement in wirelength and via cost for the 2D and 3D versions respectively, compared to the best results reported in the open literature.