MIPS R4000 Microprocessor User's Manual 361
System Interface
12.8 System Interface Cycle Time
The processor specifies minimum and maximum cycle counts for various
processor transactions and for the processor response time to external
requests. Processor requests themselves are constrained by the System
interface request protocol, and request cycle counts can be determined by
examining the protocol. The following System interface interactions can
vary within minimum and maximum cycle counts:
• spacing between requests within a cluster (cluster request
spacing)
• waiting period for the processor to release the System interface
to slave state in response to an external request (release latency)
• response time for an external request that requires a response
(external response latency).
The remainder of this section describes and tabulates the minimum and
maximum cycle counts for these System interface interactions.
Cluster Request Spacing
Processor internal activity determines the minimum and maximum
number of unused cycles allowed between the requests within a cluster.
• The minimum number of unused cycles allowed between
requests within a cluster is 0: in other words, the requests can
be adjacent.
• The maximum number of unused cycles separating requests
within a cluster varies depending on the requests that form the
cluster.
Table 12-8 summarizes the minimum and maximum number of unused
cycles allowed between requests within a cluster.
Table 12-8 Unused Cycles Separating Requests within a Cluster
From Processor
Request
To Processor
Request
Minimum Unused
SClock Cycles
Maximum Unused
SClock Cycles
Read Update 0 2
Read Write 0 2
Update Write 0 2
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