source: trunk/minix/lib/i386/misc/getprocessor.s@ 10

!       getprocessor() - determine processor type       Author: Kees J. Bot
!                                                               26 Jan 1994

.sect .text; .sect .rom; .sect .data; .sect .bss
.sect .text

! int getprocessor(void);
!       Return 386, 486, 586, ...

.define _getprocessor

_getprocessor:
        push    ebp
        mov     ebp, esp
        and     esp, 0xFFFFFFFC ! Align stack to avoid AC fault
        mov     ecx, 0x00040000 ! Try to flip the AC bit introduced on the 486
        call    flip
        mov     eax, 386        ! 386 if it didn't react to "flipping"
        jz      gotprocessor
        mov     ecx, 0x00200000 ! Try to flip the ID bit introduced on the 586
        call    flip
        mov     eax, 486        ! 486 if it didn't react
        jz      gotprocessor
        pushf
        pusha                   ! Save the world
        mov     eax, 1
        .data1  0x0F, 0xA2      ! CPUID instruction tells the processor type
        andb    ah, 0x0F        ! Extract the family (5, 6, ...)
        movzxb  eax, ah
        cmp     eax, 15         ! 15: extended family
        jne     direct
        mov     eax, 6          ! Make it 686
direct:
        imul    eax, 100        ! 500, 600, ...
        add     eax, 86         ! 586, 686, ...
        mov     7*4(esp), eax   ! Pass eax through
        popa
        popf
gotprocessor:
        leave
        ret

flip:
        pushf                   ! Push eflags
        pop     eax             ! eax = eflags
        mov     edx, eax        ! Save original eflags
        xor     eax, ecx        ! Flip the bit to test
        push    eax             ! Push modified eflags value
        popf                    ! Load modified eflags register
        pushf
        pop     eax             ! Get it again
        push    edx
        popf                    ! Restore original eflags register
        xor     eax, edx        ! See if the bit changed
        test    eax, ecx
        ret