General models and a reduction design technique for FPGA switch box designs

An FPGA switch box is said to be hyper-universal if it is detailed-routable for any set of multipin nets specifying a routing requirement over the switch box. Comparing with the known "universal switch modules", where only 2-pin nets are considered, the hyper-universal switch box model is more general and powerful. This paper studies the generic problem and proposes a systematic designing methodology for hyper-universal (k, W)-switch boxes, where k is the number of sides and W is the number of terminals on each side. We formulate this hyper-universal (k, W)-switch box design problem as a k-parfite graph design problem and propose an efficient reduction design technique. Applying this technique, we can design hyper-universal (k, W)-switch boxes with low O(W) switches for any fixed k. For illustration, we provide optimum hyper-universal (2, W) and (3, W)-switch boxes and a hyper-universal (4, W)-switch box with switch number quite close to the lower bound 6W, which is used in a well-known commercial design without hyper-universal routability. We also conclude that the proposed reduction method can yield an efficient detailed routing algorithm for any given routing requirement as well.