MIPS R10000 Microprocessor User's Manual - SGI TechPubs Library

System Interface Operations 87
External Responses
External Requests
Processor Responses
Outstanding Requests and Request Numbers
External responses are supplied by an external agent or another processor in
response to a processor request. The following external responses are supported:
• block data response
• double/single/partial-word data response
• completion response
External requests are generated by an external agent when it requires a resource
within the processor. The following external requests are supported:
• intervention shared request
• intervention exclusive request
• allocate request number request
• invalidate request
• interrupt request
External intervention and invalidate requests require some type of response by
the processor.
Processor responses are supplied by the processor in response to an external
request. The following processor responses are supported:
• coherency state response
• coherency data response
The processor allows requests and corresponding responses to be split
transactions, which enables additional processor and external requests to be
issued while waiting for a prior response. The System interface supports a request
number field to link requests with their corresponding responses, so responses
can be returned out of order.
The processor allows a maximum of eight outstanding requests on the System
interface through a 3-bit request number. These outstanding requests may be
composed of any mix of processor and external requests.
An individual processor (as opposed to the System interface, above) supports a
maximum of four outstanding processor requests at any given time.
MIPS R10000 Microprocessor User's Manual Version 2.0 of January 29, 1997