wrto.asm

一个朋友写的操作系统源码

sseg segment STACK

     db 128 dup (0)

sseg ends

dseg segment 'data'

     filename db 'test.bin','0'

dseg ends

cseg segment 'code'

     assume cs:cseg;ds:dseg

start:
      ;read MBR into 87C00 to find our partion,assume our partition ID is 23h

      mov ax,8000h
      mov es,ax
      mov bx,7c00h
      mov ax,201h
      mov dl,80h
      mov dh,0
      mov ch,0
      mov cl,1
      int 13h

      ;find out our own partion table entry

      mov si,7dbeh      ;point to the partition table
      xor cx,cx
      mov cx,4
      mov ax,8000h
      mov ds,ax

searchloop:

      cmp byte ptr [si+4],23h
      je continue       ;got it!
      dec cx
die:  je die            ;can't find
      add si,16         ;address next entry
      jmp searchloop

continue:

      ;we should save the int 13 register parameters reading from Partition table

      mov ax,[si+1]
      push ax            ;save dh(low 8bit)

      mov ax,[si+2]
      push ax            ;save cl(low 8bit)

      mov ax,[si+3]
      push ax            ;save ch(low 8bit)

      ;now we call dos file system service to read file into 87a00
      ;200h before our binary file is the head information,skimp it!

      ;open the binary file

      mov ax,dseg
      mov ds,ax
      mov dx,offset filename
      mov ax,3d00h
      int 21h

      mov bx,ax          ;file handler passed
      mov ah,3fh
      mov cx,1000h
      mov dx,8000h
      mov ds,dx
      mov dx,7a00h       ;instruction should start at 87c00
      int 21h

      mov ah,3eh         ;close the file we just opened
      int 21h

      ;55aa signature should be added at 87dfe

      mov si,7dfeh
      mov [si],0aa55h

      mov bx,8000h
      mov es,bx
      mov bx,7c00h        ;set location to be placed
      pop ax              ;pop up ch
      mov ch,al

      pop ax              ;pop up cl
      mov cl,al

      pop ax              ;pop up dh
      mov dh,al

      mov dl,80h    
      mov ax,301h
      int 13h

      mov ah,4ch          ;abort mission
      int 21h

cseg ends

end start

end