Distributed round-robin and first-come first-serve protocols and their application to multiprocessor bus arbitrary

The round-robin (RR) protocol, which uses statically assigned arbitration numbers to resolve conflict during an arbitration, is more robust and simpler to implement than previous distributed RR protocols that are based on rotating-aging priorities. The proposed first-come-first-served (FCFS) protocol uses partly static arbitration numbers, and is the first practical proposal for a FCFS arbiter known the authors. The proposed protocols have a better combination of efficiency, cost, and fairness characteristics than existing multiprocessor bus arbitration algorithms. Three implementations of the RR protocol, and two implementations of the FCFS protocol, are discussed. Simulation results are presented that address: (1) the practical potential for unfairness in the simpler implementation of the FCFS protocol: (2) the practical implications of the higher waiting-time variance in the RR protocol; and (3) the allocation of bus bandwidth among agents with unequal request rate in each protocol. The simulation results indicate that there is very little practical difference in the performance of the two protocols