Cabletron Systems, Inc.

Enterasys Networks, Inc.

William J Tiffany

Nicholas Ilyadis

Bus access is arbitrated among modules connected to a common bus. Each module has a priority level and an arbitration number assigned to it. More than one module can have the same priority level. For each priority level, the arbitration numbers assigned are unique. When two or more modules attempt bus access at the same time, the one with the higher priority level wins access. If the priority levels are the same but one module has already accessed the bus, the module that has been waiting wins access. If the modules have the same priority level and have been waiting then the module with the highest arbitration number wins access.

Method and apparatus for arbitrating bus access amongst competing devices

An arbitration unit contains a method of arbitration which includes distributed arbitration, a priority mechanism to support different classes of traffic, a unique arbitration ID bits for each module, a round robin arbitration within a given priority level to produce fair access to a bus 36, an arbitration timeout, and a bandwidth allocation between priority levels. The method of round robin bus arbitration includes the steps of providing a plurality of modules, providing a bus having a plurality of data lines, the bus connecting the plurality of modules, the bus having an arbitration unit, setting the bus to a wait state, signaling a first bus request to the bus by a first module needing to transmit a first plurality of data packets on to the bus, the first module having a first module priority level and a first unique arbitration number, signaling a second bus request to the bus by a second module needing to transmit a second plurality of data packets on to the bus, the second module having a second module priority level and a second unique arbitration number, establishing a bus priority according to a comparison of the first module priority level and the second module priority level, asserting the first unique arbitration number on the bus by the first module, asserting the second unique arbitration number on the bus by the second module, determining whether the first module and the second module have been waiting for the bus, comparing the first unique arbitration number and the second unique arbitration number, scheduling transmission of data packets in response to the steps of determining and comparing, and repeating the steps of setting, signaling, establishing, asserting, determining, comparing, and scheduling.

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Austin, TX, United States of America

William J Tiffany