Mips Technologies R4000 - Coherent Data; Noncoherent Data; System Interface Data Identifier Syntax

Chapter 12
374 MIPS R4000 Microprocessor User's Manual
System Interface Data Identifier Syntax
This section defines the encoding of the SysCmd bus for System interface
data identifiers. Figure 12-50 shows a common encoding used for all
System interface data identifiers.
Figure 12-50 Data Identifier SysCmd Bus Bit Definition
SysCmd(8) must be set to 1 for all System interface data identifiers.
NOTE: SysCmd(4) is reserved for processor data identifier. In an
external data identifier, SysCmd(4) indicates whether or not to check
the data and check bits for error.
System interface data identifiers have two formats, one for coherent data
and another for noncoherent data.
Coherent Data
Coherent data is defined as follows:
• data that is returned in response to a processor coherent block
read request
• data that is returned in response to an external intervention
request.
Noncoherent Data
Noncoherent data is defined as follows:
• data that is associated with processor block write requests and
processor doubleword, partial doubleword, word, or partial
word write requests
• data that is returned in response to a processor noncoherent
block read request or a processor doubleword, partial
doubleword, word, or partial word read request
• data that is associated with external update requests
• data that is associated with external write requests
• data that is returned in response to an external read request
• data that is associated with processor update requests.
Last
Data
1
8 7 5 4 03 2
Resp
Data
6
Err
Data
See
Note
below
Cache
State
Reserved