Intel IA-32 - Manual (Page 411)

Vol. 3A 9-37
PROCESSOR MANAGEMENT AND INITIALIZATION
.
Table 9-6. Microcode Update Field Definitions
Field Name Offset
(bytes) Length
(bytes) Description
Header Version 0 4 Version number of the update header.
Update Revision 4 4 Unique version number for the update, the basis for
the update signature provided by the processor to
indicate the current update functioning within the
processor. Used by the BIOS to authenticate the
update and verify that the processor loads
successfully. The value in this field cannot be used for
processor stepping identification alone. This is a
signed 32-bit number.
Date 8 4 Date of the update creation in binary format:
mmddyyyy (e.g. 07/18/98 is 07181998H).
Processor
Signature 12 4 Extended family, extended model, type, family, model,
and stepping of processor that requires this particular
update revision (e.g., 00000650H). Each microcode
update is designed specifically for a given extended
family, extended model, type, family, model, and
stepping of the processor.
The BIOS uses the processor signature field in
conjunction with the CPUID instruction to determine
whether or not an update is appropriate to load on a
processor. The information encoded within this field
exactly corresponds to the bit representations returned
by the CPUID instruction.
Checksum 16 4 Checksum of Update Data and Header. Used to verify
the integrity of the update header and data. Checksum
is correct when the summation of all the DWORDs
(including the extended Processor Signature Table)
that comprise the microcode update result in
00000000H.
Loader Revision 20 4 Version number of the loader program needed to
correctly load this update. The initial version is
00000001H.
Processor Flags 24 4 Platform type information is encoded in the lower 8 bits
of this 4-byte field. Each bit represents a particular
platform type for a given CPUID. The BIOS uses the
processor flags field in conjunction with the platform Id
bits in MSR (17H) to determine whether or not an
update is appropriate to load on a processor. Multiple
bits may be set representing support for multiple
platform IDs.
Data Size 28 4 Specifies the size of the encrypted data in bytes, and
must be a multiple of DWORDs. If this value is
00000000H, then the microcode update encrypted
data is 2000 bytes (or 500 DWORDs).