MIPS R10000 Microprocessor User's Manual - SGI TechPubs Library

102 Chapter 6.
SysAD[63:0] Encoding
SysAD[63:0] Address Cycle Encoding
SysAD[63:60]
This section describes the system address/data bus encoding.
Table 6-21 presents the encoding of the SysAD[63:0] bus for address cycles.
Table 6-21 Encoding of SysAD[63:0] for Address Cycles
During the address cycle of processor noncoherent block read, double/single/
partial-word read, block write, double/single/partial-word write, and eliminate
requests, the processor always drives a target indication of 0 on SysAD[63:60].
This indicates that the request targets the external agent only. When the
CohPrcReqTar mode bit is negated, during the address cycle of processor
coherent block read and upgrade requests, the processor also drives a target
indication of 0 on SysAD[63:60]. However, when the CohPrcReqTar mode bit is
asserted, during the address cycle of processor coherent block read and upgrade
requests, the processor drives a target indication of 0xF on SysAD[63:60]. This
indicates that the request targets all processors, together with the external agent,
on the cluster bus. In multiprocessor systems using the cluster bus, the
CohPrcReqTar mode bit is asserted for a snoopy-based coherency protocol, and
negated for a duplicate tag or directory-based coherency protocol.
When the processor is in slave state, an external agent uses the target indication
field to specify which processors are targets of an external request.
SysAD[59:58] Uncached Attribute
SysAD[63:60] Target Indication
SysAD[63] Target processor with DevNum = 3
SysAD[62] Target processor with DevNum = 2
SysAD[61] Target processor with DevNum = 1
SysAD[60] Target processor with DevNum = 0
SysAD[59:58] Uncached attribute
SysAD[57] Secondary cache block way indication
SysAD[56:40] Reserved
SysAD[39:0] Physical address
During the address cycle of processor double/single/partial-word read and write
requests and during the address cycle of processor Uncached accelerated block write
requests, the processor drives the uncached attribute onto SysAD[59:58]. See the
section titled, Support for Uncached Attribute, in this chapter for more
information.
Version 2.0 of January 29, 1997 MIPS R10000 Microprocessor User's Manual