'Delayed layering' three layer channel routing

In the paper, a new three-layer channel router with 'delayed layering' technique is presented. The delayed layering scheme in the routing can improve the capability of the router to reach comprehensive objectives. This new router not only minimises the tracks used, but also minimises the via usage and maximises the use of preferred routing layers. The delayed layering router consists of two steps: track assignment and layer assignment. The track assignment uses a topological sorting algorithm to determine the horizontal track number of every net. A layerless layout will result from the track assignment. The layer assignment heuristically determines which layers can be used for routing the wire segments in the layerless layout, such that the vias generated are as small as possible.