A Description of the Computer Simulation of a New Bus Arbitration Scheme

The object of bus arbitration schemes is to provide fair access to the bus by the various elements of the computer system. Arbitration must allow for each element to have access to the bus while, at the same time, preventing any signal element from monopolizing the bus. The method of bus arbitration presented here appears to meet these goals. The arbitration scheme described in this report places the various elements of the system on a rotating system of priorities. After the various priorities are set initially O...N-1, where N is the number of system elements all the priorities are incremented by one on a modulo N basis. In this way, each processor will eventually have top priority and be able to take possession of the bus if needed. In a simulation of this scheme using a random mix of bus demands, the average wait of any processor for the bus was very short, generally less than 10 bus cycles bus cycle defined in the body of the report. For simulations in which the bus demand was high a probability of requesting the bus of 0.75 and a probability of retaining the bus of 0.75, the average delay was seven cycles. The simulation program itself is described in detail and the results of various combinations of probabilities are presented.