calling interrupts directly

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Hayden

Joined: 06 Oct 2005
Posts: 132

Hayden 15 Mar 2007, 20:55

Doe's anyone know the correct procedure to make a far call to an interrupt?
I've been reading the 'intel software developers manual' but its just all a bit to cumbersome for me at the moment.

Code:

ORG 100H
USE16

start:

    mov bx, 10h
    add bx, bx
    add bx, bx

    sidt [IDTDesc]

    les di, [IDTBase + bx]

    mov ax, 19
;    int 10h

;    pushf
    call far [es:di]

    xor ax, ax
    int 16h
    int 20h

IDTDesc:
    IDTLimit dw ?
    IDTBase  dd ?

_________________
New User.. Hayden McKay.

15 Mar 2007, 20:55

vid
Verbosity in development

Joined: 05 Sep 2003
Posts: 7103
Location: Slovakia

vid 15 Mar 2007, 21:25

what's wrong about using "int" instruction?

15 Mar 2007, 21:25

Hayden

Joined: 06 Oct 2005
Posts: 132

Hayden 15 Mar 2007, 21:48

just playin' around with unfamiliar instructions LGDT, LIDT etc... and this
was my first attempt to try something dumb.

15 Mar 2007, 21:48

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8466
Location: Kraków, Poland

Tomasz Grysztar 15 Mar 2007, 22:00

LES won't work for you here, and why do you add BX to IDTBase offset? You should rather add it to contents of [IDTBase]. This may look like:

Code:

ORG 100H
USE16

start:

    mov ebx,10h
    add ebx,ebx
    add ebx,ebx

    sidt [IDTDesc]

    mov eax,[IDTBase]
    add eax,ebx
    mov di,ax
    and di,0FFFh
    shr eax,16-4
    mov es,ax

    mov ax, 19
;    int 10h

    pushf
    call far dword [es:di]

    xor ax, ax
    int 16h
    int 20h

IDTDesc:
    IDTLimit dw ?
    IDTBase  dd ?

Well, cannot test it under Windows environment, because SIDT gives the Windows' IDT instead of the 16-bit one - which is by standard at 0 address anyway. Wink

15 Mar 2007, 22:00

Hayden

Joined: 06 Oct 2005
Posts: 132

Hayden 30 Apr 2007, 16:24

i've created some dos interrupt code that chains to the last handler via the pushf far call method wich led me back to this thread.

Quote:

LES won't work for you here, and why do you add BX to IDTBase offset? You should rather add it to contents of [IDTBase].

Thanks TG. I can now see the error of my ways Laughing

_________________
New User.. Hayden McKay.

30 Apr 2007, 16:24

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