ISR hook

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DustWolf

Joined: 26 Jan 2006
Posts: 373
Location: Ljubljana, Slovenia

DustWolf 25 Sep 2007, 18:11

Hello,

I'm making my first kernel and sortof at the phase of laying the foundation for my CPU scheduler. I need a Timer ISR hook. I was translating this from some other dialect and the far pointers translation to FASM wasn't exactly obvious... So I'm wondering if I got it about right:

ISR Hook:

Code:

ISRnewTimerInstall:
        cli
        mov     ax,cs       ;data is where the code is
        mov     ds,ax
        mov     ax, 0       ;ISR routing table is in sector 0
        mov     es,ax
        mov     ax,[es:32]  ;8 (as int  * 4
        mov     bx,[es:34]  ;8 (as int  * 4 + 2
        mov     [ISRoldTimerOffset],ax
        mov     [ISRoldTimerSegment],bx
        mov     [es:32],word ISRnewTimerOffset
        mov     [es:34],word cs
        sti

ISR Routine:

Code:

ISRnewTimerOffset:
        cli
        sti
        jmp far dword [ISRoldTimerOffset]
ISRoldTimerOffset       dw      ?
ISRoldTimerSegment      dw      ?

Does it appear right?

Thanks for any help. Smile

25 Sep 2007, 18:11

mikegonta

Joined: 20 Nov 2005
Posts: 99

mikegonta 25 Sep 2007, 21:31

[ Post removed by author. ]

Last edited by mikegonta on 27 Jan 2009, 22:00; edited 2 times in total

25 Sep 2007, 21:31

DustWolf

Joined: 26 Jan 2006
Posts: 373
Location: Ljubljana, Slovenia

DustWolf 26 Sep 2007, 18:06

mikegonta wrote:

Assemble your 32 bit protected mode program with ORG 100000h (1 meg), rename it "start" and copy it to the FAT12 disk.

While I do appreciate the program you have created and am aware that it would help to simplify quite a lot in various cases a lot like mine.... my Kernel does not use file systems, much less FAT12, nor would I like to rely on any other software while testing my basic concepts for implementability.

26 Sep 2007, 18:06

mikegonta

Joined: 20 Nov 2005
Posts: 99

mikegonta 27 Sep 2007, 00:39

[ Post removed by author. ]

Last edited by mikegonta on 27 Jan 2009, 22:01; edited 2 times in total

27 Sep 2007, 00:39

Dex4u

Joined: 08 Feb 2005
Posts: 1601
Location: web

Dex4u 27 Sep 2007, 03:33

@DustWolf, here are two fasm examples:
16bit real mode example, from MiniDos

Code:

;====================================================;;  set interrupt vector                              ;;====================================================;int21_25:  cmp   al,19h                       ; No change int 19h (for rebooting)        je    int21_error                  ; Jump to int21_error label        cli                                ; Turn off int's        xor   ah,ah                        ; 0 AH        shl   ax,2                         ; Mul whats in AX by 4        push  si                           ; Save SI        push  bx                           ; Save BX        push  es                           ; Save ES        mov   si,ax                        ; Move AX into SI        xor   bx,bx                        ; 0 BX        mov   es,bx                        ; Move BX into ES        mov   word[es:si],dx              ; Move offset address to ES:SI points to.        mov   bx, ds                       ; Move DS into BX        mov   word[es:si+2],bx                 ; Move segment of address to ES:SI+2 points too.        pop   es                           ; Restore ES        pop   bx                           ; Restore BX        pop   si                           ; Restore SI        sti                                ; Turn int's on       jmp int21_exit                     ; Jump to int21_exit label;====================================================;;  Get interrupt vector                              ;;====================================================;int21_35:        push  ds                           ; Save DS        push  si                           ; Save SI    xor   ah,ah                        ; 0 AH        shl   ax,2                         ; Mul whats in AX by 4        mov   si,ax                        ; Move AX into SI        xor   bx,bx                        ; 0 BX        mov   ds,bx                         ; DS = 0        mov   bx,word[ds:si+2]            ; Move the word that DS:SI+2 points to, into BX        push bx                            ; Save BX        mov   bx,word [ds:si]            ; Move the word that DS:SI points to, into BX        pop es                               ; Move what was in the pushed BX into ES        pop si                             ; Restore SI        pop ds                             ; Restore DS jmp   int21_exit                   ; Jump to int21_exit label

pmode 32bit example from "TITANSRC"

Code:

  get_int_vector:                  ; AL = interrupt number       movzx   eax,al        shl     eax,3 add     eax,10800h              ; add address of IDT  cli   mov     cx,word [ds:eax+2]  ; get selector        mov     [esp+18h],cx            ; return selector in CX       mov     dx,word [ds:eax+6]        shl     edx,16        mov     dx,word [ds:eax]  mov     [esp+14h],edx           ; return offset in EDX        sti   jmp     int_ok  set_int_vector:                   ; CX:EDX - interrupt handler      movzx   eax,al                  ; AL = interrupt number       shl     eax,3 add     eax,10800h              ; add address of IDT  cli   mov     word [ds:eax+2],cx  ; store selector      mov     word [ds:eax],dx    ; store offset        shr     edx,16        mov     word [ds:eax+6],dx        sti   jmp     int_ok

27 Sep 2007, 03:33

DustWolf

Joined: 26 Jan 2006
Posts: 373
Location: Ljubljana, Slovenia

DustWolf 27 Sep 2007, 22:24

Dex4u: Thanks! Could you just also add the code of the 16 bit version where the dx value is derived for the interrupt set? Also I could use some code on how to do an interrupt routine (only basic structure relevant) and continue into another.

mikegonta: I'm not coding in 16 bit mode, my loader is in 16 bit mode. As such it is not relying on anything in it's runtime, only at load-time which can be dismissed. The BIOS extender you are offering, regardless of how valuable it is in most cases, is a hack and thus an undefined variable which will make the results of my idea-exploring harder to interpet.

27 Sep 2007, 22:24

Dex4u

Joined: 08 Feb 2005
Posts: 1601
Location: web

Dex4u 28 Sep 2007, 02:36

DustWolf wrote:

Dex4u: Thanks! Could you just also add the code of the 16 bit version where the dx value is derived for the interrupt set? Also I could use some code on how to do an interrupt routine (only basic structure relevant) and continue into another.

Sure, as MiniDos is a Dos clone, its the same as calling int 21h, function 25h from dos
example:

Code:

xor ax,axmov ds,ax                        mov ah,25hmov al,9hmov dx,int9hhandlerint 21h;some stuff hereint9hhandler:;some stuff hereiret

Note: the above code would be called from a user program.

Also the full code to MiniDos is here: http://board.flatassembler.net/topic.php?t=5275

28 Sep 2007, 02:36

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