A new global routing algorithm for FPGAs

As in traditional ASIC technologies, FPGA routing usually consists of two steps: global routing and detailed routing. Unlike existing FPGA detailed routers, which can take full advantage of the special structures of the programmable routing resources, FPGA global routing algorithms still greatly resemble their counter-parts in the traditional ASIC technologies. In particular, the routing congestion information of a switch block essentially is still measured by the numbers of available rows and columns in the switch block. Since the internal architecture of a switch block decides what can route through the block, the traditional measure of routing capacity is no longer accurate. In this paper, we present an accurate measure of switch block routing capacity. Our new measure considers the exact positions of the switches inside a switch block. Experiments with a global router based on these ideas show an average improvement of 38% in the channel width required to route some benchmark circuits using a popular switch block, compared with an algorithm based on the traditional methods for congestion control.