Intel 64 and IA-32 Architectures Software Developers Manual Volume 3A, System Programming Guide, Part 1

Vol. 3A 9-57
PROCESSOR MANAGEMENT AND INITIALIZATION
9.11.8.5 Function 00H—Presence Test
This function verifies that the BIOS has implemented required microcode update
functions. Table 9-13 lists the parameters and return codes for the function.
In order to assure that the BIOS function is present, the caller must verify the carry
flag, the return code, and the 64-bit signature. The update count reflects the number
of 2048-byte blocks available for storage within one non-volatile RAM.
The loader version number refers to the revision of the update loader program that is
included in the system BIOS image.
Table 9-13. Parameters for the Presence Test
Input
AX Function Code 0D042H
BL Sub-function 00H - Presence test
Output
CF Carry Flag Carry Set - Failure - AH contains status
Carry Clear - All return values valid
AH Return Code
AL OEM Error Additional OEM information.
EBX Signature Part 1 'INTE' - Part one of the signature
ECX Signature Part 2 'LPEP'- Part two of the signature
EDX Loader Version Version number of the microcode update loader
SI Update Count Number of 2048 update blocks in NVRAM the BIOS
allocated to storing microcode updates
Return Codes (see Table 9-18 for code definitions
SUCCESS The function completed successfully.
NOT_IMPLEMENTED The function is not implemented.