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MultiProcessor Specification
A-4 Version 1.4
mov esi,LVT1
mov eax,[esi] ; read LVT1
and eax,0FFFE00
FFH ; not masked, edge, active high
or eax,000005700H ; ExtInt
mov [esi],eax ; write LVT1
;
; Program LVT2 as NMI, which delivers the signal on the NMI signal of all
; processors' cores listed in the destination.
;
mov esi,LVT2
mov eax,[esi] ; read LVT2
and eax,0FFFE00
FFH ; not masked, edge, active high
or eax,000005400H ; NMI
mov [esi],eax ; write LVT2
extrn pmode_off : near
call pmode_off ; switch back to real mode
pop ax ; restore imr settings
out 0a1h,al ; restore secondary imr
pop ax
out 021h,al ; restore primary imr
; this routine leaves NMI disabled
pop esi ; restore regs used in APIC init
pop es ; (unless also saved for CPUID)
pop ds
ret
InitLocalAPIC endp
Example A-1. Programming Local APIC for Virtual Wire Mode (continued)
A.4 Constructing the MP Configuration Table
For a compliant system, one of the main functions of the system BIOS is to construct the MP
floating pointer structure and the MP configuration table. Because the MP configuration table is
optional, the BIOS must set the MP feature information bytes in the MP floating pointer structure
to indicate whether an MP configuration table is present.
If the MP configuration table is required, the BIOS constructs it in conjunction with the BSP and
APs. The BIOS is responsible for synchronizing the activities of the APs during the construction
of the table. The BIOS may need some synchronization during processor initialization so that each
processor may be brought up in the proper order. The mechanism for synchronization is not
specified; however, the procedure described in the following paragraphs of this section uses AP
status flags as an example of a synchronization mechanism. This procedure also initializes the APs
serially. System developers may employ other mechanisms and may initialize all processors in
parallel to minimize the system start-up time.
The BIOS maintains an initialized AP status flag for each AP. Each AP will begin executing the
same BIOS code as the BSP, but will eventually be put in a HALT state or held in a loop until the
BSP enables its AP status flag.