Controlling requests for access to resources made by multiple processors over a shared bus

A data processing system comprising a plurality of processors that access multiple resources over a bus shared by said processors, and a system memory connected to the bus for storing entries each of which corresponds to one of said resources and designates whether said resource is available for use,

• each of said processors comprising
• a processing unit for generating a request for access to one of said resources, said request identifying said resource,
• a local memory for storing copies of said system memory entries, and
• a controller for examining said copies of said entries stored in said local memory in response to said request to determine whether said resource identified in said request is available for use by said processing unit, said controller preventing said request from being transmitted over said bus if one of said copies of said entries stored in said local memory designates said identified resource as being unavailable, and otherwise transmitting said request over said bus, said controller comprising
• means for determining when said identified resource has become available, and
• means for updating the copy of said entry stored in said local memory that corresponds to said identified resource to indicate that said identified resource has become available in response to said determining, said controller thereafter permitting a subsequent request for access to said identified resource to be transmitted over said bus.

A data processing system comprising

• a plurality of processors interconnected by a bus, said processors having a plurality of possible modes of operation, and
• a system memory connected to said bus, said system memory including a plurality of entries each of which corresponds to one of said modes of operation and indicates whether said mode is available for use by one of said processors,
• each of said processors including:
• a processing unit for generating a request to operate in one of said modes, said request identifying said mode,
• a local memory for storing copies of said system memory entries, and
• a controller for examining said copies of said entries stored in said local memory in response to said request to determine whether said mode identified in said request is available for use by said processing unit, said controller preventing said request from being transmitted over said bus if one of said copies of said entries stored in said local memory designates said mode identified in said request as being unavailable, and otherwise transmitting said request over said bus.

A method for operating a processor in a data processing system that includes a plurality of processors which access multiple resources over a bus shared by said processors, and a system memory connected to the bus for storing a table of entries each of which corresponds to one of said resources and designates whether said resource is available for use, said method comprising

• generating a request for access to one of said resources, said request identifying said resource,
• storing in a local memory in said processor copies of said system memory entries,
• examining said copies of said entries stored in said local memory in response to said request for access to determine whether said resource identified in said request is available for use,
• preventing said request from being transmitted over said bus if one of said copies of said entries stored in said local memory designates said identified resource as being unavailable, and otherwise transmitting said request over said bus,
• determining when said identified resource has become available,
• updating the copy of said entry stored in said local memory that corresponds to said identified resource to indicate that said identified resource has become available in response to said determining, and
• thereafter permitting a subsequent request for access to said identified resource to be transmitted over said bus.

In a data processing system comprising a plurality of processors each of which accesses multiple resources over a bus shared by said processors, and a system memory connected to the bus for storing entries each of which corresponds to one of said resources and designates whether said resource is available for use, a method of operating each of said processors, comprising

• generating a request for access to one of said resources, said request identifying said resource,
• storing in a local memory in said processor copies of said system memory entries,
• examining said copies of said entries stored in said local memory in response to said request for access to determine whether said resource identified in said request is available for use,
• preventing said request from being transmitted over said bus if one of said copies of said entries stored in said local memory designates said identified resource as being unavailable, and otherwise transmitting said request over said bus,
• determining when said identified resource has become available,
• updating the copy of said entry stored in said local memory that corresponds to said identified resource to indicate that said identified resource has become available in response to said determining, and
• thereafter permitting a subsequent request for access to said identified resource to be transmitted over said bus.

In a data processing system that includes a plurality of processors interconnected by a bus, said processors having a plurality of possible modes of operation, a method comprising

• storing in a system memory connected to said bus a plurality of entries each of which corresponds to one of said modes of operation and indicates whether said mode is available for use by one of said processors,
• causing each of said processors to:
• generate a request to operate in one of said modes, said request identifying said mode,
• store in a local memory copies of said system memory entries,
• examine said copies of said entries stored in said local memory in response to said request for access to determine whether said mode identified in said request is available for use,
• prevent said request from being transmitted over said bus to said system memory if one of said copies of said entries stored in said local memory designates said mode identified in said request as being unavailable, and otherwise transmit said request to said system memory over said bus.

A computer system comprising

• a plurality of processors connected to a bus for executing a computer program,
• a system memory connected to the bus and storing said computer program, said system memory including entries each of which corresponds to a region of said computer program and designates whether said region is available for processing by one of said processors,
• each one of said processors including
• a processing unit for executing said computer program and generating an access request for a selected one of said regions of said computer program,
• a local memory for storing copies of said system memory entries, and
• a controller for examining said copies of said entries stored in said local memory in response to said access request to determine whether said selected one of said regions is available for processing by said processing unit, said controller preventing said access request from being transmitted over the bus if one of said copies of said entries stored in said local memory designates said selected region as being unavailable, and otherwise transmitting said access request over the bus.