flat assembler - Jump in TSR proc

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jentos

Joined: 30 Mar 2004
Posts: 8
Location: Russia

jentos 23 Feb 2007, 13:15

Hi all!
Can somebody tell me please what wrong in this code?
I try create simple TSR programm, initialisation going quite well Smile

Smile

, but in "MyInt" instruction "jmp far dword [OldInt]" don`t jump to saved interrupt Sad

Sad

. I try also "jmp far dword [cs:OldInt]", but at all work the same Sad

Sad

.

Code:

        org     100h
        use16
;--------------------------------------------------------------------
        jmp init
OldInt: dd      0
;-------------------------------------------------------------------
MyInt:
        jmp far dword [OldInt]
;---------------------------------------------------
init:   mov     ax,3508h
        mov     word [OldInt+2],es
        mov     word [OldInt],bx
        int     21h
        ;
        mov     ax,2508h
        mov     dx,MyInt
        int     21h
        ;
        mov     ah,9
        mov     dx,Mes
        int     21h
        ;
        mov     dx,init
        int     27h
        ;
Mes     db 'TSR...',13,10,'$'

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23 Feb 2007, 13:15

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Goplat

Joined: 15 Sep 2006
Posts: 181

Goplat 23 Feb 2007, 19:38

jentos: You do have to jump through [CS:OldInt] since DS could be anywhere. There's another problem though: your code for getting the original vector is wrong. It needs to be like this

Code:

init:   mov     ax,3508h
        int     21h
        mov     word [OldInt+2],es
        mov     word [OldInt],bx

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23 Feb 2007, 19:38

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jentos

Joined: 30 Mar 2004
Posts: 8
Location: Russia

jentos 24 Feb 2007, 07:55

Embarassed

Thank you!
Smile

Smile

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24 Feb 2007, 07:55

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