A “greedy” channel router

• Authors: Ronald L. Rivest;Charles M. Fiduccia
• Venue: DAC '82 Proceedings of the 19th Design Automation Conference
• Year: 1982

We present a new, “greedy”, channel-router that is quick, simple, and highly effective. It always succeeds, usually using no more than one track more than required by channel density. (It may be forced in rare cases to make a few connections “off the end” of the channel, in order to succeed.) It assumes that all pins and wiring lie on a common grid, and that vertical wires are on one layer, horizontal on another. The greedy router wires up the channel in a left-to-right, column-by-column manner, wiring each column completely before starting the next. Within each column the router tries to maximize the utility of the wiring produced, using simple, “greedy” heuristics. It may place a net on more than one track for a few columns, and “collapse” the net to a single track later on, using a vertical jog. It may also use a jog to move a net to a track closer to its pin in some future column. The router may occasionally add a new track to the channel, to avoid “getting stuck”.