Optical bus control for distributed multiprocessors

Abstract

Optical interconnections offer a potential for gigahertz transfer rates in an environment free from capacitive bus loading, crosstalk, and electromagnetic interference. Device technology in electrooptics has matured to a point where small, low power, and low cost devices exist which are suitable for use in bus level implementations. Therefore, the realization of physically distributed, bus-interconnected multiprocessors is now possible. In this paper we propose a bus arbitration mechanism suitable for a large optical bus structure heavily populated with asynchronous bus masters. It is a two-level arbitration system with incoming requests hatched on a demand basis and serviced in a linear priority order within each batch. Low priority requests cannot be starved in high contention environments. For an optical bus of fixed length, propagation delay is bounded by the end-to-end transit time and is independent of the number of devices attached. In addition, as contention for the bus increases and batch sizes become larger, the time overhead paid for bus control decreases. Thus, a performance improvement is achieved dynamically under high contention conditions.