Intel IA-32 - Manual (Page 435)

Vol. 3A 9-61
PROCESSOR MANAGEMENT AND INITIALIZATION
9.11.8.7 Function 02H—Microcode Update Control
This function enables loading of binary updates into the processor. Table 9-15 lists the parame-
ters and return codes for the function.
Description
This control is provided on a global basis for all updates and processors. The caller can deter-
mine 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 9-16 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.
Table 9-15. 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 9-18 for code definitions)
SUCCESS Function completed successfully.
READ_FAILURE A failure occurred because of the inability to read the storage
device.
Table 9-16. 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.