Switchbox routing by stepwise reshaping

An algorithm for switchbox routing, called PACKER, is presented. In an initial phase, the connectivity of each net is established in a fast way without taking the other nets into account. In general this will give rise to conflicts (short circuits). In the second stage the conflicts are removed iteratively using Connectivity preserving local transformations (CPLT’s). They “reshape” a net by displacing one of its segments without disconnecting it from the net. The transformations are applied in a systematic way using a scan-line technique. During this process, a subset of the segments at the position of the scan line are densely packed in the (two) layers available for routing. The remaining segments are pushed to the next scan-line position. Scanning in the four available directions (from left to right, right to left, top to bottom, and bottom to top) is performed until all conflicts have disappeared or no solution is found within a maximum number of iterations. It turns out that the new approach to routing, as implemented in PACKER, also has practical merits: most of the well-known “benchmark” examples are solved.