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Index > OS Construction > debugging BOOTMOSF

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viki



Joined: 03 Jan 2006
Posts: 40
Location: Czestochowa, Poland
viki
Based on BOOTMOSF.asm from MenuetOS I've prepared version you can debug in dos mode using for example td.exe. I prepared also small kernel for test. To test it please copy kernel.bin on floppy and run td boot.com.

kernel.asm

Code:
  org 0h

  mov  si,beg_txt
  call disp_txt
  retf

;-------------------------------------------------------------------------
disp_txt:
;-------------------------------------------------------------------------
  lodsb
  or   al,al
  jz   @f
  mov  ah,0eh
  mov  bx,07h
  int  010h
  jmp  disp_txt
@@:
  ret

beg_txt db "Kernel loaded",0  
    


boot.asm

Code:
  pos_read_tmp    equ 0700h ;position for temporary read
  boot_program    equ 07c00h ;position for boot code
  seg_read_kernel equ 01000h ;seguiment to kernel read
  org  100h

  jmp start
  nop

  OEM_ID            db 'KOLIBRI '
  BytesPerSector    dw 512
  SectorsPerCluster db 1
  ReservedSectors   dw 1
  TotalFATs         db 2
  MaxRootEntries    dw 224
  TotalSectorsSmall dw 2880
  MediaDescriptor   db 0f0h
  SectorsPerFAT     dw 9
  SectorsPerTrack   dw 18
  NumHeads          dw 2
  HiddenSectors     dd 0
  TotalSectorsLarge dd 0
  DriveNumber       db 0
  Flags             db 0
  Signature         db 029h
  VolumeID          dd 12
  VolumeLabel       db 'KOLIBRI    '
  SystemID          db 'FAT12   '

;-------------------------------------------------------------------------
start:
;-------------------------------------------------------------------------
  cld
  mov  ax,ss
  mov  [old_ss],ax
  mov  [old_sp],sp

  mov  ax,9000h ; segment for stack
  mov  ss,ax
  mov  sp,boot_program

  mov  si,msg_load
  call disp_txt

  push ss
  pop  es
  mov  ax,020eh ;read, 14 sectors for directory
  mov  bx,pos_read_tmp ;es:bx read position
  mov  cx,02h ;track 0, sector 2
  mov  dx,0100h ;head 1, drive 0 (aSmile
  call read_sector
  mov  di,bx

loop_find_kernel:
  mov  cx,11 ;file name
  mov  si,kernel_name
  rep  cmpsb
  je   load_fat
  add  di,21
  cmp  di,pos_read_tmp+(512*14) ;end of directory
  jb   loop_find_kernel

disp_err:
  mov  si,msg_err
  call disp_txt

load_fat:
  mov  bp,[es:di+15] ;starting cluster
  mov  [cluster1st], bp

  mov  ax,0209h ;read, 9 sectors
  mov  bx,pos_read_tmp ;es:bx read position
  mov  cx,02h ;track 0, sector 2
  xor  dx,dx ;head 0, drive 0 (aSmile
  call read_sector
  jc   disp_err
  mov  ax,seg_read_kernel
  mov  es,ax
  xor  bx,bx

loop_read_kernel:
  call read_floppy
  jc   disp_err

  push bx
  mov  bx,es
  add  bx,0x20
  mov  es,bx
  pop  bx

  mov  di,bp
  shr  di,01h
  pushf
  add  di,bp
  add  di,pos_read_tmp
  mov  ax,[ss:di]
  popf
  jc   even_sector
  and  ax,0fffh
  jmp  if_last_sector
even_sector:
  mov  cl,4
  shr  ax,cl
if_last_sector:
  cmp  ax,0ff8h
  jae  run_kernel
  mov  bp,ax
  jmp  loop_read_kernel

;-------------------------------------------------------------------------
run_kernel:
;-------------------------------------------------------------------------
  push word seg_read_kernel
  pop  ds
  push cs
  push 0
  push word seg_read_kernel
  push word 00h
  retf

koniec:
  cli
  mov  sp,[old_sp]
  mov  ax,[old_ss]
  mov  ss,ax
  sti
  ret

;-------------------------------------------------------------------------
disp_txt:
;-------------------------------------------------------------------------
  lodsb
  or   al,al
  jz   @f
  mov  ah,0eh
  mov  bx,07h
  int  010h
  jmp  disp_txt
@@:
  ret

;-------------------------------------------------------------------------
read_floppy: ;es:bx -> position in read buffer
;-------------------------------------------------------------------------
  ;bp -> logical sector to read
  ;carry <- 0 read OK
  ;carry <- 1 read error
  push bx
  mov  ax,0e5fh ;underline
  xor  bh,bh
  int  010h
  pop  bx
  mov  ax,bp ;data sector to read
writesec:
  add  ax,31 ;get logical sector
  mov  cx,36 ;sector/track
  xor  dx,dx
  div  cx
  mov  ch,al ;track transfer
  xor  dh,dh ;head 0
  cmp  dl,18
  jb   @f
  sub  dl,18
  inc  dh ;head 1
@@:
  inc  dl
  mov  cl,dl
  xor  dl,dl ;drive 0 (aSmile
patchhere:
  mov  ax,0201h ;read 1 sector
  call read_sector
  retn

;-------------------------------------------------------------------------
read_sector:
;-------------------------------------------------------------------------
  push bp
  mov  bp,20
@@:
  dec  bp
  jz   disp_err
  push ax bx cx dx
  int  0x13
  pop  dx cx bx ax
  jc   @b
  pop  bp
  retn

old_ss       dw  ?
old_sp       dw  ?

msg_load:    db  "Loading VikiOS v0.01 - 2006.04.01",13,10,"Please Wait...",0
msg_err:     db  "FDD read error",0
kernel_name  db 'KERNEL  BIN'
cluster1st   dw ?
loader_block dw 1
                         
Post 18 Apr 2006, 11:54
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