Browse Prior Art Database

Method for Decreasing Arbitration Overhead

IP.com Disclosure Number: IPCOM000047736D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Bergey, AL: AUTHOR [+2]

Abstract

This invention is a method for decreasing the arbitration overhead required to transfer messages on a shared multiprocessor bus. It can be used whenever a given processor uses the bus more than one time in a row. It decreases arbitration overhead by overlapping arbitration with the beginning of the message. This invention is a variation of central arbitration. A multiprocessor bus with central arbitration is composed of several users, the bus, and a central arbiter. Each user sends a signal, Request, to the arbiter. The arbiter sends a signal, Grant, to each user. If a user wants to use the bus, it first activates Request. If that request is the only request active, the central arbiter replies with Grant immediately. If more than one request is active, the central arbiter chooses one, and issues Grant to that one.

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Method for Decreasing Arbitration Overhead

This invention is a method for decreasing the arbitration overhead required to transfer messages on a shared multiprocessor bus. It can be used whenever a given processor uses the bus more than one time in a row. It decreases arbitration overhead by overlapping arbitration with the beginning of the message. This invention is a variation of central arbitration. A multiprocessor bus with central arbitration is composed of several users, the bus, and a central arbiter. Each user sends a signal, Request, to the arbiter. The arbiter sends a signal, Grant, to each user. If a user wants to use the bus, it first activates Request. If that request is the only request active, the central arbiter replies with Grant immediately. If more than one request is active, the central arbiter chooses one, and issues Grant to that one. After the chosen one has finished using the bus, the central arbiter issues Grant to one of the other users. After each user has been serviced, Grant to that user is lowered. Before each user can use the bus, it must first arbitrate, or activate Request and wait for Grant. This operation adds overhead delay to both the bus user and the bus itself. This invention eliminates the arbitration delay in the case where a given processor uses the bus more than one time in a row. It does this with the following modifications to centralized arbitration: 1. If no other user requests the bus, Grant is not deactivated after a...