9-42 Vol. 3A

PROCESSOR MANAGEMENT AND INITIALIZATION

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Issue the Update Control function with Task = Enable.

9.11.8.3   Microcode Update Functions

Table 9-13 defines the processor microcode update functions that implementations of INT 15H 0D042H must 
support.

9.11.8.4   INT 15H-based Interface

If an OEM-BIOS is implementing INT 15H 0D042H interface and offer to its client, the BIOS should allow additional 
microcode updates to be added to system flash.
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 9-14 lists the 
parameters and return codes for the function.

Table 9-13.  Microcode Update Functions 

Microcode Update Function

Function 

Number

Description

Required/Optional

Presence test

00H

Returns information about the supported functions.

Required

Write update data

01H

Writes one of the update data areas (slots).

Required

Update control

02H

Globally controls the loading of updates.

Required

Read update data

03H

Reads one of the update data areas (slots).

Required

Table 9-14.  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