Directional bias and non-uniformity in FPGA global routing architectures

We investigate the effect of the prefabricated routing track distribution on the area-efficiency of FPGAs. The first question we address is whether horizontal and vertical channels should contain the same number of tracks (capacity), or if there is a density advantage with a directional bias. Secondly, should the channels have a uniform capacity, or is there an advantage when capacities vary from channel to channel? The key result is that the most area-efficient global routing architecture is one with uniform (or very nearly uniform) channel capacities across the entire chip in both the horizontal and vertical directions. Several non-uniform and directionally-biased architectures, however are fairly area-efficient provided that appropriate choices are made for the pin positions on the logic blocks and the logic array aspect ratio.