Intel IA-32 - Manual (Page 426)

9-52 Vol. 3A
PROCESSOR MANAGEMENT AND INITIALIZATION
•
The calling program should read any update data that already exists in the BIOS in order to
make decisions about the appropriateness of loading the update. The BIOS must refuse to
overwrite a newer update with an older version. The update header contains information
about version and processor specifics for the calling program to make an intelligent
decision about loading.
•
There can be no ambiguous updates. The BIOS must refuse to allow multiple updates for
the same CPU to exist at the same time; it also must refuse to load updates for processors
that don’t exist on the system.
•
The calling application should implement a verify function that is run after the update
write function successfully completes. This function reads back the update and verifies that
the BIOS returned an image identical to the one that was written.
Example 9-12 represents a calling program.
Example 9-12. INT 15 DO42 Calling Program Pseudo-code
//
// We must be in real mode
//
If the system is not in Real mode exit
//
// Detect the presence of Genuine Intel processor(s) that can be updated
// using(CPUID)
//
If no Intel processors exist that can be updated exit
//
// Detect the presence of the Intel microcode update extensions
//
If the BIOS fails the PresenceTestexit
//
// If the APIC is enabled, see if any other processors are out there
//
Read IA32_APICBASE
If APIC enabled
{
Send Broadcast Message to all processors except self via APIC
Have all processors execute CPUID and record the Processor Signature
(i.e.,Extended Family, Extended Model, Type, Family, Model, Stepping)
Have all processors read IA32_PLATFORM_ID[52:50] and record Platform
Id Bits
If current processor cannot be updated
exit
}
//
// Determine the number of unique update blocks needed for this system
//
NumBlocks = 0