Intel IA-32 - Manual (Page 542)

14-16 Vol. 3A
MACHINE-CHECK ARCHITECTURE
The 4-bit RRRR sub-field (see Table 14-7) indicates the type of action associated with the error.
Actions include read and write operations, prefetches, cache evictions, and snoops. Generic
error is returned when the type of error cannot be determined. Generic read and generic write
are returned when the processor cannot determine the type of instruction or data request that
caused the error. Eviction and snoop requests apply only to the caches. All of the other requests
apply to TLBs, caches and interconnects.
The bus and interconnect errors are defined with the 2-bit PP (participation), 1-bit T (time-
out), and 2-bit II (memory or I/O) sub-fields, in addition to the LL and RRRR sub-fields (see
Table 14-8). The bus error conditions are implementation dependent and related to the type of
bus implemented by the processor. Likewise, the interconnect error conditions are predicated
on a specific implementation-dependent interconnect model that describes the connections
between the different levels of the storage hierarchy. The type of bus is implementation depen-
dent, and as such is not specified in this document. A bus or interconnect transaction consists
of a request involving an address and a response.
Table 14-7. Encoding of Request (RRRR) Sub-Field
Request Type Mnemonic Binary Encoding
Generic Error ERR 0000
Generic Read RD 0001
Generic Write WR 0010
Data Read DRD 0011
Data Write DWR 0100
Instruction Fetch IRD 0101
Prefetch PREFETCH 0110
Eviction EVICT 0111
Snoop SNOOP 1000