Intel IA-32 - Manual (Page 430)

9-56 Vol. 3A
PROCESSOR MANAGEMENT AND INITIALIZATION
Description
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.
9.11.8.6 Function 01H—Write Microcode Update Data
This function integrates a new microcode update into the BIOS storage device. Table 9-14 lists
the parameters and return codes for the function.
Table 9-14. Parameters for the Write Update Data Function
Input
AX Function Code 0D042H
BL Sub-function 01H - Write update
ES:DI Update Address Real Mode pointer to the Intel Update structure. This buffer is
2048 bytes in length if the processor supports only fixed-size
microcode update or...
Real Mode pointer to the Intel Update structure. This buffer is
64 KBytes in length if the processor supports a variable-size
microcode update.
CX Scratch Pad1 Real mode segment address of 64 KBytes of RAM block
DX Scratch Pad2 Real mode segment address of 64 KBytes of RAM block
SI Scratch Pad3 Real mode segment address of 64 KBytes of RAM block
SS:SP Stack pointer 32 KBytes of stack minimum
Output
CF Carry Flag Carry Set - Failure - AH Contains status
Carry Clear - All return values valid
AH Return Code Status of the call
AL OEM Error Additional OEM information
Return Codes (see Table 9-18 for code definitions
SUCCESS The function completed successfully.
NOT_IMPLEMENTED The function is not implemented.
WRITE_FAILURE A failure occurred because of the inability to write the storage
device.
ERASE_FAILURE A failure occurred because of the inability to erase the storage
device.
READ_FAILURE A failure occurred because of the inability to read the storage
device.