Detailed Routing

The detailed-routing phase follows the global-routing phase in the two-phase approach to routing. Recall that the global-routing phase constructs routes that are paths in a routing graph whose edges represent routing regions. For the purpose of detailed routing, these edges have to be expanded to give an accurate graph representation of the respective routing region. The resulting detailedrouting graph looks very much like the routing grids used in area routing with the exception that it is (almost) always planar. However, in contrast to the area-routing problem, the input now contains not only a set of nets, but also a global route for each net. This route specifies how the net maneuvers around the obstacles in the routing region that are defined by the cells of the circuit. The detailed-routing problem is to find detailed routes through the routing graph that comply with the global routes and that obey a certain set of constraints. The constraint set is the detailed-routing model.