Universal switch modules for FPGA design

Abstract

A switch module M with W terminals on each side is said to be universal if every set of nets satisfying the dimensional constraint (i.e., the number of nets on each side of M is at most W ) is simultaneously rout able through M . In this article, we present a class of universal switch modules. Each of our switch modules has 6 W switches and switch-module flexibility three (i.e, F s =3). We prove that no switch module with less than 6 W switches can be universal. We also compare our switch modules with those used in the Xilinx XC4000 family FPGAs and the antisymmetric switch modules (with F S =3) suggested by Rose and Brown [1991]. Although these two kinds of switch modules also have F S =3 and 6 W switches, we show that they are not universal. Based on combinatorial counting techniques, we show that each of our universal switch modules can accommodate up to 25% more routing instances, compared with the XC4000-type switch module of the same size. Experimental results demonstrate that our universal switch modules improve routability at the chip level. Finally, our work also provides a theoretical insight into the important observation by Rose and Brown [1991] (based on extensive experiments) that F S =3 is often sufficient to provide high routability.