Hierarchical global wiring for custom chip design

Abstract

We present a global wiring algorithm used in a top-down physical design environment, i.e. macros are laid out only after global wiring is done, and wires are allowed to pass through macros (wiring-through model). The floorplan of the chip is in the form of a slicing structure. The algorithm is based on a hierarchical scheme. The final result is obtained through a series of refinement as the problem is recursively decomposed into a set of small-sized problems and then solved efficiently. Given a balanced slicing tree representation of the floorplan, the worst-case running time of the overall algorithm is 0(MN), where M is the number of macros and N the number of nets. The algorithm has been implemented in the C language and has been used for actual chip design. Experiments showed that the hierarchical router performs better than a flat maze type router in wireability handling, equally well in wire length, and much faster in run-time (at least 10 times for an example with 100 macros and 1000 nets, and the gap being even larger for bigger sized problems).