MIPS R10000 Microprocessor User's Manual - SGI TechPubs Library

100 Chapter 6.
During data cycles, SysCmd[4:3] indicate the data type, as shown in Table 6-17.
Processor block write and double/single/partial-word write requests use request
data and request last data type indications. External data and processor coherency
data responses use response data and response last data type indications.
Table 6-17 Encoding of SysCmd[4:3] for Data Cycles
SysCmd[4:3] Data type Indication
0 Request data
1 Response data
2 Request last
3 Response last
During data cycles of an external block data response or processor coherency data
response, SysCmd[2:1] contain the state of the cache block, as shown in Table 6-18.
Table 6-18 Encoding of SysCmd[2:1] for Block Data Responses
SysCmd[2:1] Cache Block State
0 Reserved
1 Shared
2 CleanExclusive
3 DirtyExclusive
During data cycles, SysCmd[0] specifies whether ECC checking and correcting is
to be performed for the SysAD[63:0] bus, as shown in Table 6-19. During
processor data cycles, the processor asserts SysCmd[0]. Consequently, in a
multiprocessor system using the cluster bus, ECC checking and correcting will be
enabled for external block data responses resulting from processor coherency data
responses.
Table 6-19 Encoding of SysCmd[0] for External Data Cycles
SysCmd[0] ECC check indication
0 ECC checking and correcting disable
1 ECC checking and correcting enable
Version 2.0 of January 29, 1997 MIPS R10000 Microprocessor User's Manual