Interconnect power and delay optimization by dynamic programming in gridded design rules

The lithography used for 32 nanometers and smaller VLSI process technologies restricts the admissible interconnect widths and spaces to a small set of discrete values with some interdependencies, so that traditional interconnect sizing by continuous-variable optimization techniques becomes impossible. We present a dynamic programming (DP) algorithm for simultaneous sizing and spacing of all wires in interconnect bundles (or bus structures), yielding the optimal power-delay tradeoff curve. It sets the width and spacing of all interconnects simultaneously, thus finding the global optimum. The DP algorithm is generic and can handle a variety of power-delay objectives, such as total power or delay, or weighted sum of both, power-delay product, max delay and alike. The algorithm consistently yields more than 10% dynamic power and 5% delay reduction for interconnect channels in industrial microprocessor blocks designed in 32 nanometer process technology, when applied as a post-layout optimization step to redistribute wires within interconnect channels of fixed width, without changing the area of the original layout.