Intel IA-32 - Manual (Page 429)

Vol. 3A 9-55
PROCESSOR MANAGEMENT AND INITIALIZATION
9.11.8.4 INT 15H-based Interface
Intel recommends that a BIOS interface be provided that allows additional microcode updates
to be added to system flash. The INT15H interface is the Intel-defined method for doing this.
The program that calls this interface is responsible for providing three 64-kilobyte RAM areas
for BIOS use during calls to the read and write functions. These RAM scratch pads can be used
by the BIOS for any purpose, but only for the duration of the function call. The calling routine
places real mode segments pointing to the RAM blocks in the CX, DX and SI registers. Calls to
functions in this interface must be made with a minimum of 32 kilobytes of stack available to
the BIOS.
In general, each function returns with CF cleared and AH contains the returned status. The
general return codes and other constant definitions are listed in Section 9.11.8.9, “Return Codes.”
The OEM error field (AL) is provided for the OEM to return additional error information
specific to the platform. If the BIOS provides no additional information about the error, OEM
error must be set to SUCCESS. The OEM error field is undefined if AH contains either
SUCCESS (00H) or NOT_IMPLEMENTED (86H). In all other cases, it must be set with either
SUCCESS or a value meaningful to the OEM.
The following sections describe functions provided by the INT15H-based interface.
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.
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.