wrfpy.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 'floppy.bin','0'
     binbuf   db  512 dup (0)
     suc      db 'boot block patched successful!','$'

dseg ends

cseg segment 'code'

     assume cs:cseg;ds:dseg;es:dseg

     extrn panic:near,printf:near

start:

      ; write floppy.bin into sector 0 of floppy diskette

      ; open floppy.bin

      mov ax,dseg
      mov ds,ax
      mov es,ax

      push bp
      mov bp,sp
      sub sp,2

      mov dx,offset filename
      mov ax,3d00h
      int 21h
      jnc wnext1
      push ax
      call panic
wnext1:

      ; move fp to skip DOS exe header

      mov bx,ax
      xor cx,cx
      mov dx,512
      mov al,0
      mov ah,42h
      int 21h
      jnc wnext2
      push ax
      call panic
wnext2:
      mov dx,offset binbuf
      mov ah,3fh
      mov cx,512
      int 21h
      jnc wnext3
      push ax
      call panic
wnext3:

      ;close it

      mov ah,3eh
      int 21h

      mov word ptr [bp-2],5     ; init retry times
wretry:
      mov bx,offset binbuf
      mov ax,301h
      mov dl,0
      mov dh,0
      mov ch,0
      mov cl,1
      int 13h

      mov ah,1              ; check the error code
      int 13h
      cmp ah,0
      je wnext4
      cmp word ptr [bp-2],0
      jne wnext5
      mov al,ah
      xor ah,ah
      add ax,6
      push ax
      call panic
wnext5:
      dec word ptr [bp-2]

      ; reset controller

      mov ah,0
      int 13h
      jmp wretry 

wnext4:

      mov ax,offset suc
      push ax
      call printf
      pop cx

      mov ah,4ch
      int 21h

cseg ends

end start