1 BoxRouter: A New Global Router Based on Box Expansion and Progressive ILP Minsik Cho and David Z. Pan ECE Dept. Univ. of Texas at Austin DAC 2006, July 24-28

2 Introduction Global Routing – plans approximate route of each net to reduce complexity of detailed router Goal: Optimize wire density during global routing –Improve manufacturability –Potential to feedback interconnect information

3 Steps PreRouting captures congested areas BoxRouting starts in most congested area and expands box to cover entire chip Progressive integer linear programming (ILP) technique to route wires in box Maze routing algorithm for rest of wires PostRouting reroutes wires without rip-up –Parameter controls trade-off between length and routability

4 BoxRouter Route as many wires inside box as possible with ILP Maze routing algorithm if ILP fails

5 Algorithm

6 Steps 1) PreRouting – Identify congested area 2) Box around congested area 3) ILP routing between G-cells 4) Maze routing5) Expand box 6) Repeat

7 PostRouting Start from congested area Reroute wires to reduce length (if possible) Reroute surrounding wires Repeat Parameter controls cost function –Wirelength vs. routability

8 Experimental Results Larger box expansion can improve results at a cost of runtime Compared to Labyrinth –Reduce wirelength by 14.3% –Reduce overflow by 91.7% Compared to Fengshui –Reduce overflow by 79% Compared to multicommodity flow-based router –15.7x faster –4.2% shorter wirelength