-System Interface Data Identifier Syntax

12.9 System Interface Commands and Data Identifiers

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.

Data Identifier Bit Definitions

SysCmd(7) marks the last data element and SysCmd(6) indicates whether or not the data is response data, for both processor and external coherent and noncoherent data identifiers. Response data is data returned in response to a read request or an intervention request.

SysCmd(5) indicates whether or not the data element is error free. Erroneous data contains an uncorrectable error and is returned to the processor, forcing a bus error. In the case of a block response, the entire line must be delivered to the processor no matter how minimal the error. The processor delivers data with the good data bit deasserted if a primary parity error is detected for a transmitted data item. If the system is in ECC mode, a secondary cache data ECC error is detected by comparing the values transmitted on the SysAD and SysADC.

SysCmd(4) indicates to the processor whether to check the data and check bits for this data element, for both coherent and noncoherent external data identifiers.

SysCmd(3) is reserved for external data identifiers.

SysCmd(4:3) are reserved for both coherent and noncoherent processor data identifiers.

SysCmd(2:0) indicate the data cache state to load the cache line, in response to processor coherent read requests for coherent data identifiers. SysCmd(2:0) also indicate the cache state for response data to an external intervention request, or for the data cycle issued in response to an external snoop request. SysCmd(2:0) are reserved for noncoherent data identifiers.

Table 12-25 lists the encodings of SysCmd(7:3) for processor data identifiers. Table 12-26 lists the encodings of SysCmd(7:3) for external data identifiers. Table 12-27 lists the encodings of SysCmd(2:0) for coherent data identifiers.

Table 12-25 Processor Data Identifier Encoding of SysCmd(7:3)

Table 12-26 External Data Identifier Encoding of SysCmd(7:3)

Table 12-27 Coherent Data Identifiers Encoding of SysCmd(2:0)

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