Optimal global interconnects for GSI

Abstract

Performance of a high-speed chip is largely affected by both latency and bandwidth of global interconnects, which connect different macrocells. Therefore, one of the important goals is to design high-bandwidth and fast buses that connect a processor and its on-chip cache memory or link different processors within a multiprocessor chip. In this paper, the width of global interconnects is optimized to achieve a large and a small latency simultaneously. Data-flux density is the product of interconnect bandwidth and reciprocal wire pitch, which represents the number of bits per second that can be transferred across a unit-length bisectional line. The optimal wire width, which maximizes the product of data-flux density and reciprocal latency, is independent of interconnect length and can be used for all global interconnects. It is rigorously proved that the optimal wire width is the width that results in a delay that is 33% larger than the time-of-flight (ToF). Using the optimal wire width decreases latency, energy dissipation, and repeater area considerably, compared to a sub-optimal wire width (e.g., 42% smaller latency, 30% smaller energy-per-bit, and 84% smaller repeater area compared with the W/sub opt//2 case) at the cost of a small decrease in data-flux density (e.g., 14% smaller compared with W/sub opt//2 case). A super-optimal wire width, however, causes a slight decrease in latency (e.g., 14% for 2W/sub opt/) at the cost of a large decrease in data-flux density (e.g., 35% for 2W/sub opt/).