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Token-style-arbitration-on-a-serial-bus-by-passing-an-unrequested-bus-grand-signal-and-returning-the-token-by-a-token-refusal-signal

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Token style arbitration on a serial bus by passing an unrequested bus grand signal and returning the token by a token refusal signal

Details

Inventors: Duckwall, William S.;
Assignee: Apple Computer, Inc. (Cupertino, CA)
Primary Examiner: Dung; Dinh C.
Assistant Examiner:
Attorney, Agent or Firm: Blakely, Sokoloff, Taylor & Zafman

An electronic system comprises a plurality of components each having at least one communication node and being coupled together by communication links through the respective communication nodes so that the plurality of communication links and communication nodes form a bus which resembles an acyclic directed graph having established hierarchical parent-child relationships between adjacent nodes and a root node. Token passing style arbitration is implemented on the system, in one embodiment, in response to the root node sending out an unrequested bus grant, so that the node with the token has access to the bus.

DETAILED DESCRIPTION It is an object of the present invention to enhance the functionality of a computer system bus in which the nodes of the bus have been resolved into an acyclic directed graph.
This and other objects of the present invention are implemented in a computer system in which the various components of the system are interconnected via nodes on a communications bus.
In one embodiment, once the topology of the nodes has been resolved into an acyclic directed graph, and the nodes have gone through an initialization process, the nodes are allowed to arbitrate for control of the bus in accordance with a token passing method.
During the arbitration, a metaphorical token is passed through the acyclic directed graph in an order determined by predetermined selection criterion each node has established for selecting adjacent nodes.
Provisions can be made for other arbitration methods, such as fair bus access arbitration.

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