MIPS R4000 Microprocessor User's Manual 337
System Interface
Processor Cluster Request Protocol
In secondary-cache mode, the processor can issue two types of requests:
individual and cluster.
All of the requests that are part of a cluster must be accepted by the
external agent before a response to the read request, that began the cluster,
can be returned to the processor. A cluster consists of:
• a processor read with write forthcoming request followed by a
write request
• a processor read request followed by a potential update request
• a processor read with write forthcoming request followed by a
potential update request, followed by a write request.
Figure 12-23 illustrates a cluster consisting of a read with write
forthcoming request, followed by a potential update request, followed by
a coherent block write request for eight words of data (with minimum
spacing between the requests that form the cluster), followed by an
uncompelled change to slave state at the earliest opportunity.
NOTE: Timings for the SysADC and SysCmdP buses are the same as
those of the SysAD and SysCmd buses, respectively. There may be
unused cycles between the requests that form a cluster.
Figure 12-23 Processor Cluster Request Protocol
SCycle
1 2 3 4 5 6 7 8 9 10 11 12
SClock
SysAD Bus
Addr Addr Data0 Addr Data0 Data1 Data2 Data3
SysCmd Bus
RwWF Upd CEOD Write CData CData CData CEOD
ValidOut*
ValidIn*
RdRdy*
WrRdy*
Release*
4
1
Master Slave
2
3
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