Chapter 12
304 MIPS R4000 Microprocessor User's Manual
Processor Requests
A processor request is a request or a series of requests, through the System
interface, to access some external resource. As shown in Figure 12-7,
processor requests include read, write, null write, invalidate, and update.
This section also describes clusters.
Figure 12-7 Processor Requests
Read request asks for a block, doubleword, partial doubleword, word, or
partial word of data either from main memory or from another system
resource.
Write request provides a block, doubleword, partial doubleword, word, or
partial word of data to be written either to main memory or to another
system resource.
Null write request indicates that an expected write has been cancelled as a
result of an external request.
Invalidate request specifies a line in every other cache in the system that
must be marked invalid.
Update request provides a block, doubleword, partial doubleword, word,
or partial word of data that must be transferred to every other cache in the
system.
Table 12-1 lists the processor requests that each type of R4000 can issue.
Table 12-1 Supported Processor Requests
Request R4000PC R4000SC R4000MC
Processor Read X X X
Processor Write X X X
Processor Null Write X X
Processor Invalidate X
Processor Update X
R4000
External Agent
Processor Requests
• Read
• Write
• Null write
• Invalidate
• Update
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