Integrated Rerouting

Abstract

It is generally true that routers which sequentially embed nets one at a time suffer both from their lack of foresight and lack of hindsight. They lack foresight because they fail to anticipate the consequences that embedding a net will have on those nets yet to be routed. Likewise, they lack hindsight because of their inability to modify previous routing decisions in response to the unforeseen needs of a currently routing net. The foresight problem is usually addressed with heuristic route-ordering and various congestion-avoidance strategies. Because these relatively simple measures often fail to provide reliable completion, it frequently proves necessary to attack the hindsight problem as well. This is done by giving the router a capability to rip-up previously embedded nets, which is the subject of this chapter.