Permutation Channel Routing

Most of the channel routing algorithms in the literature [Deut76, YoKu82, RiFi82, BuPe83, ReSS85] including the simulated annealing channel routers studied in Chapter 4 assume a model in which the pins on the two sides of the channel are fixed (both physically and logically.) Other models that reflect less stringent physical constraints have also been studied. In [GoCW83], it was assumed that only the relative ordering of the pins is fixed. The pins are allowed to “shift” horizontally. This model captures the possibility of expanding or contracting the dimensions of a cell. In [LeLi83] and [Leon86a], the discretionary channel routing problem in which only some of the pins in a given net need to be interconnected was studied. This model captures the possibility of having physically equivalent pins or duplicated pins in a cell. As expected, such flexibilities lead to better routing results, namely, fewer tracks are required for interconnection.