Vol. 3A 9-47

PROCESSOR MANAGEMENT AND INITIALIZATION

This control is provided on a global basis for all updates and processors. The caller can determine the current status 
of update loading (enabled or disabled) without changing the state. The function does not allow the caller to disable 
loading of binary updates, as this poses a security risk.
The caller specifies the requested operation by placing one of the values from Table 9-17 in the BH register. After 
successfully completing this function, the BL register contains either the enable or the disable designator. Note that 
if the function fails, the update status return value is undefined.

The READ_FAILURE error code returned by this function has meaning only if the control function is implemented in 
the BIOS NVRAM. The state of this feature (enabled/disabled) can also be implemented using CMOS RAM bits 
where READ failure errors cannot occur. 

9.11.8.8   Function 03H—Read Microcode Update Data

This function reads a currently installed microcode update from the BIOS storage into a caller-provided RAM buffer. 
Table 9-18 lists the parameters and return codes. 

Table 9-16.  Parameters for the Control Update Sub-function

Input
AX

Function Code

0D042H

BL

Sub-function

02H - Control update

BH

Task

See the description below.

CX

Scratch Pad1

Real mode segment of 64 KBytes of RAM block

DX

Scratch Pad2

Real mode segment of 64 KBytes of RAM block

SI

Scratch Pad3

Real mode segment of 64 KBytes of RAM block

SS:SP

Stack pointer

32 kilobytes 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. 

BL

Update Status

Either enable or disable indicator

Return Codes (see Table 9-19 for code definitions)
SUCCESS

Function completed successfully.

READ_FAILURE

A failure occurred because of the inability to read the storage device. 

Table 9-17.  Mnemonic Values

Mnemonic

Value

Meaning

Enable

1

Enable the Update loading at initialization time.

Query

2

Determine the current state of the update control without changing its status.

Table 9-18.  Parameters for the Read Microcode Update Data Function

Input
AX

Function Code

0D042H

BL

Sub-function

03H - Read Update

ES:DI

Buffer Address

Real Mode pointer to the Intel Update structure that 

will be written with the binary data