MIPS R4000 Microprocessor User's Manual 369
System Interface
Null Requests
Figure 12-45 shows the format of a SysCmd null request.
Figure 12-45 Null Request SysCmd Bus Bit Definition
Processor null write requests, System interface release external null
requests, and secondary cache release external null requests all use the
null request command. Table 12-18 lists the encodings of SysCmd(4:3) for
processor null write requests. Table 12-19 lists the encodings of
SysCmd(4:3) for external null requests.
SysCmd(2:0) are reserved for both instances of null requests.
Table 12-18 Processor Null Write Request Encoding of SysCmd(4:3)
Table 12-19 External Null Request Encoding of SysCmd(4:3)
SysCmd(4:3) Null Write Attributes
0 Null write
1 Reserved
2 Reserved
3 Reserved
SysCmd(4:3) Null Attributes
0 System Interface release
1 Secondary cache release
2 Reserved
3 Reserved
011
0
8 7 5 4 03 2 1
Null Request Specific
(see tables)
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