Heuristic strategies for switchbox routing in VLSI design

A two-layer symbolic router is proposed which is able to route very dense switchbox problems successfully. The heuristics on which the routing program is based emulate the approach followed by expert designers in manual routing. First, the most promising connections are looked for, without affecting the wireability of more complex connections. Secondly, in crowded situations, blocking nets are identified and alternative solutions are tied through rip-up and rerouting steps. These heuristics greatly extend the space for searching the solution, thus markedly increasing its rate of success