Distributed arbitration apparatus and method for shared bus

In a computer system having a multiplicity of subunits connected to a shared bus, distributed arbitration apparatus comprising:

• an arbitration bus having a separate channel for each said subunit;
• and
• a multiplicity of arbitration means, each coupled to the shared bus, the arbitration bus and to a corresponding one of the subunits, for determining the priority by which said subunits shall access said shared bus;
• each said arbitration means determining only whether said subunit coupled to said arbitration means is to be granted access to said shared bus;
• each said arbitration means including:
• status means for storing a multiplicity of status signals denoting which of said subunits have priority over the subunit corresponding to said arbitration means;
• bus requesting means coupled to said arbitration bus for asserting a bus request signal on the channel of said arbitration bus corresponding to said arbitration means;
• and
• access control means, coupled to said arbitration bus and said status means, for comparing bus request signals asserted on the channels of said arbitration bus with corresponding ones of said status signals stored in said status means, and for granting the corresponding subunit access to said shared bus only if none of said bus request signals correspond to status signals denoting subunits having higher priority than said corresponding subunit.

In a computer system having a multiplicity of subunits connected to a shared bus, arbitration apparatus comprising:

• an arbitration bus having a separate channel for each other said subunit;
• and
• a multiplicity of arbitration means, each coupled to the shared bus, the abitration bus and to a corresponding one of the subunits, for determining the priority by which said subunits shall access said shared bus;
• each said arbitration means determining only whether said subunit coupled to said arbitration means is to be granted access to said shared bus;
• each said arbitration means including:
• status means for storing status signals denoting which ones of said subunits have higher priority and which ones have lower priority than the subunit corresponding to said arbitration means;
• bus requesting means coupled to said arbitration bus for asserting a bus request signal on the channel of said arbitration bus corresponding to said arbitration means;
• and
• access control means, coupled to said arbitration bus and said status means, for receiving bus request signals asserted on said arbitration bus and for granting the corresponding subunit access to said shared bus only when said bus requesting means has asserted a bus request signal and none of said received bus request signals correspond to subunits denoted by said status means as having higher priority than said corresponding subunit.

In a computer system having a multiplicity of subunits interconnected by an arbitration bus with means for carrying a multiplicity of substantially simultaneous bus request signals, a method of arbitrating access by said subunits to a shared bus, the steps of the method comprising performing, substantially simultaneously, the following steps at each subunit:

• storing a distinct set of status signals denoting which ones of said subunits have higher priority and which ones have lower priority than said subunit;
• asserting a bus request signal on said arbitration bus when said subunit needs access to said shared bus;
• comparing said bus request signals asserted on said arbitration bus with said status signals for said subunit;
• and
• granting said subunit access to said shared bus only when said subunit has asserted a bus request signal and none of said bus request signals correspond to subunits denoted by said status signals as having higher priority than said subunit;
• whereby each subunit simultaneously arbitrates access to the shared bus.

In a computer system having a multiplicity of subunits interconnected by an arbitration bus with means for carrying a multiplicity of substantially simultaneous bus request signals, a method of arbitrating access by said subunits to a shared bus, the steps of the method comprising:

• storing, for each subunit, a distinct set of status signals denoting which ones of said subunits have higher priority and which ones have lower priority than said subunit;
• asserting on said arbitration bus a separate bus request signal for each of those subunits which need access to said shared bus;
• and
• substantially simultaneously, at each one of said subunits which asserted a bus request signal, comparing said bus request signals asserted on said arbitration bus with said stored status signals for said subunit and granting said subunit access to said shared bus only if none of said bus request signals correspond to subunits denoted by said stored status signals as having higher priority than said subunit;
• whereby each subunit simultaneously arbitrates access to the shared bus.