Chapter 12
302 MIPS R4000 Microprocessor User's Manual
12.4 Processor and External Requests
There are two broad categories of requests: processor requests and external
requests. These two categories are described in this section.
When a system event occurs, the processor issues either a single request or
a series of requests—called processor requests—through the System
interface, to access an external resource and service the event. For this to
work, the processor System interface must be connected to an external
agent that is compatible with the System interface protocol, and can
coordinate access to system resources.
An external agent requesting access to processor caches or to a processor
status register generates an external request. This access request passes
through the System interface. System events and request cycles are shown
in Figure 12-5.
Figure 12-5 Requests and System Events
R4000
External Agent
Processor Requests
• Read
• Write
• Null write
• Invalidate
• Update
External Requests
• Read
• Write
• Null
• Invalidate
• Update
• Snoop
• Intervention
System Events
• Load Miss
• Store Miss
• Store Hit
• Uncached Load/Store
• CACHE operations
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