A First-Come-First-Serve Bus-Allocation Scheme Using Ticket Assignments

Abstract

This paper describes a new scheme for allocating a data bus on a first-come-first-serve (FCFS) basis. When the devices connected to the bus request to become the bus-master, they are assigned distinct “ticket numbers” in the order in which the requests are generated, at which time they go into a wait state. When the bus is released by a device holding the ticket number n, it is then allocated to the device holding the ticket number n + 1. We discuss the conditions under which the scheme is a close approximation to the ideal FCFS scheme and evaluate its performance using simulation results. We also present two alternative hardware implementations of this scheme — one centralized and the other distributed. Because of its simple hardware implementation, the scheme is attractive for applications where a bus is shared, in an unbiased fashion, among a large number of devices.