Fault-Tolerant Arbitration in Multichip Crossbar Switches

A major problem in the design of large multichip crossbar networks is the latency associated with the centralized controller used to arbitrate requests. We present a solution to reduce this latency and also provide fault-tolerance by the use of multiple controllers that can operate concurrently. This paper concentrates on crossbars that are constructed using one-sided crosspoint switches, as such designs can alleviate simultaneous switching noise. Two arbitration mechanisms are proposed that provide a range of trade-oos in controller complexity and hardware overheads. We derive a lower bound on the number of busses required for any distributed control scheme and compare it with simulation results for a 64 port network. The results show that besides reducing arbitration latencies, distributed control can provide almost non-blocking operation with little extra hardware, and with improved properties of fault-tolerance and graceful degradation.