Arbitration among multiple users of a shared resource

Abstract

Arbitration is performed among a plurality of users for access to a shared resource in a system of the kind in which the users arbitrate by placing arbitration signals on a line and subsequently comparing their arbitration signals with a signal appearing on the line, by providing the users with independently operating clocks, and controlling the progression of the arbitration based on timing provided by the clock of at least one of the users. The progression of the arbitration thus does not depend upon a single master clock, or upon synchronizing the individual user clocks. Users that request access are assigned a first priority in the arbitration based at least on an access priority preassigned to the request for access and on whether the user is a member of a current group of users that is formed at a time during the arbitration when another group of users is empty, the current group including users that have been denied access as of that time; at least a portion of each user's arbitration signal is arranged as a multibit word having a value that represents the first priority, and each user that arbitrates for access places its multibit word in parallel on the path and determines whether it has won the arbitration by subsequently comparing its multibit word value with the value of a multibit word that appears on the path.