MIPS R4000 Microprocessor User's Manual 317
System Interface
External Snoop Request
An external snoop request makes the processor inspect the secondary
cache to see if the cache contains a valid version of the specified cache line.
If the valid cache line is present, the processor reports the cache line state
and can modify this state.
An external snoop request is complete after the processor returns the state
of the specified cache line.
External Intervention Request
When an external agent issues an intervention request, the specified
secondary cache line is inspected. Upon inspection, the cache line state is
reported and/or modified. Under certain circumstances the specified
cache line may also be retrieved. The external intervention request is
complete after one of the following occurs:
• the processor returns the state of the specified cache line
• the processor returns the last word of data for the specified
cache line.
Read Response
A read response returns data in response to a processor read request, as
shown in Figure 12-13. While a read response is technically an external
request, it has one characteristic that differentiates it from all other
external requests—it does not perform System interface arbitration. For
this reason, read responses are handled separately from all other external
requests, and are simply called read responses.
Figure 12-13 Read Response
R4000
External Agent
1. Read request
2. Read response
To Next Page
Loading...