US 4,229,791 AGranted

Distributed arbitration circuitry for data processing system

AssigneeDigital Equipment Corporation

InventorsJohn V. Levy, David Rodgers, Robert E. Stewart, David Potter, Richard J. Casabona

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Abstract

A digital data processing system including an interconnection for the various elements that constitute the system. Each element that connects to the interconnection is called a nexus, and each nexus in the system can communicate with other nexuses on a priority basis. A central clocking circuit generates timing signals that control such communications by defining bus cycles on a synchronous basis and each nexus contains priority circuitry that operates in response to these signals. Each nexus that requires access to the interconnection asserts a transfer request signal at a predetermined time during each bus cycle. Priority arbitration circuitry in each nexus receives all such requests and samples them at another, later, time during each bus cycle. When a nexus is transmitting a request and no nexus with a higher priority is transmitting a request, that nexus takes control of the interconnection. A transfer during a subsequent bus cycle to another nexus can be prevented during certain types of transfers.

Claims16

Dependent claims

A data processing system including a bus means with arbitration conductor means, timing conductor means and information transfer conductor means and including a plurality of nexus means connected to said bus means, at least one said nexus means comprising:

A. timing means connected to said timing conductor means for establishing iteratively a sequence of control states,
B. information transfer means connected to said information transfer conductor means for affecting an exchange of information over said information conductor means with another of said nexus means,
C. priority assignment means for establishing for said nexus means a priority level that is unique to said nexus means,
D. request means connected to said timing means and said information transfer means for generating during a first control state a priority request signal onto said arbitration conductor means when said information transfer means is prepared to affect an exchange of information, said priority request signal having a priority corresponding to the priority level established for said nexus means by said priority assignment means,
E. priority receiver means connected to said arbitration conductor means for receiving at least the priority request signals from all said other nexus means having a higher priority than said nexus means, and
F. comparison means connected to said priority receiver means, said priority assignment means and said timing means for enabling said information transfer means to affect an information exchange when said nexus means generates a priority request signal having the highest priority level during a given sequence of control states.

3 more elements

A nexus means for exchanging information with other nexus means connected thereto by a bus means with arbitration conductor means, timing conductor means and information transfer conductor means, said nexus means comprising:

A. timing means that connects to the timing conductor means for establishing iteratively a sequence of control states,
B. information transfer means that connects to said information transfer conductor means for affecting an exchange of information over the information conductor means with another of said nexus means,
C. priority assignment means for establishing for said nexus means a priority level that is unique to said nexus means,
D. request means connected to said timing means and said information transfer means for generating selectively a priority request signal during a first control state that has a priority corresponding to the level established by said priority assignment means,
E. priority receiver means that connects to the arbitration conductor means for receiving at least the priority request signals from all other nexus means having a higher priority level than said nexus means, and
F. comparison means connected to said priority receiver means, said priority assignment means and said timing means for enabling said information transfer means to affect an information exchange whenever said nexus means generates a priority request signal having the highest priority level in the data processing system.

3 more elements

Dependencies are inferred from the claim text.