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NASM Forum => Using NASM => Topic started by: nobody on September 03, 2007, 06:56:34 PM

Title: HI some help here
Post by: nobody on September 03, 2007, 06:56:34 PM

i want to know how did u put a booting program on an diskett.
I have this program:
Boot record is loaded at 0000:7C00,
   ORG 7C00h
; load message address into SI register:
   LEA SI,[msg]
; screen function:
   MOV AH,0Eh
print:  MOV AL,[SI]
   CMP AL,0
   JZ done      ; zero byte at end of string
   INT 10h      ; write character to screen.
        INC SI
   JMP print

; wait for 'any key':
done:   MOV AH,0
       INT 16h      ; waits for key press
         ; AL is ASCII code or zero
         ; AH is keyboard code

; store magic value at 0040h:0072h to reboot:
;      0000h - cold boot.
;      1234h - warm boot.
   MOV  AX,0040h
   MOV  DS,AX
   MOV  word[0072h],0000h   ; cold boot.
   JMP  0FFFFh:0000h    ; reboot!

msg    DB  'Welcome, I have control of the computer.',13,10
   DB  'Press any key to reboot.',13,10
   DB  '(after removing the floppy)',13,10,0

i use nasm to assemble it but after that i dont know how to save it in a diskett ahy help would be nice

THX, Cesar

Title: Re: HI some help here
Post by: nobody on September 03, 2007, 07:38:42 PM

Hi Cesar,

I'd use dd. If your development OS doesn't have that, you could use "rawwrite", or John Fine's "partcopy", or DEBUG will do it (have to format the disk first - PITA!).

Or... since you claim to have control of the computer, you could write one. :)

Here's a start...

Best,
Frank

P.S. Your bootsector assumes that ds is zero. This may or may not be true - depends on the bios. If it doesn't work, that's probably why. If it does work on your machine, it may not work on another. As the Masm folks say, "Assume Nothing! :)

Having said that, *this* file assumes that your bootsector is named "boot.bin", and is going on a: :)

; nasm -f bin -o writeit.com writeit.asm

[BITS 16]
[ORG 0x100]
  mov  ax,3D00h
  mov  dx,filename
  int  21h
  ; check for errors here!
  mov  bx,ax
  mov  ah,3Fh
  mov  dx,buffer
  mov  cx,512
  int  21h
  ; check for errors here!
  mov  ah,3Eh
  int  21h

push ds
  pop  es
 mov bx, buffer
 mov dl, 00h
 mov dh, 0
 mov cl, 1
 mov ch, 0
 mov ah, 03h
 mov al, 1
  int  13h

mov ax, 4C00h
 int 21h

filename  db 'BOOT.BIN',0

buffer    times 512 db 0

Title: Re: HI some help here
Post by: nobody on September 03, 2007, 08:45:38 PM

Thanks i will try that now