kernel/fat12/fat12.asm

   1 ;----------------------------------------------------------;
   2 ; BOS kernel                Christoffer Bubach, 2012-2015. ;
   3 ;----------------------------------------------------------;
   4 ;                                                          ;
   5 ;    FAT12 driver.                                         ;
   6 ;                                                          ;
   7 ;----------------------------------------------------------;
   8       struc disk
   9       {
  10           .disk_number         db  0                  ; which disk?
  11           .root_dir            dw  0                  ; position of rootdir
  12           .fat_1               dd  0                  ; position of fat1
  13           .fat_2               dd  0                  ; position of fat2
  14           .data_area           dw  0                  ; position of dataarea
  15           .disk_size           dd  0
  16           .free_space          dd  0
  17           .boot                bootsector
  18           ; ..... some other values
  19       }
  20       struc bootsector                                ; 512 bytes
  21       {
  22           .jumper              db  0,0,0
  23           .oem                 db  0,0,0,0,0,0,0,0
  24           .sectorsize          dw  0
  25           .sect_per_clust      db  0
  26           ;.... more values here
  27       }
  28
  29       virtual at 0
  30           bootsector bootsector
  31           sizeof.bootsector = $
  32       end virtual
  33
  34       virtual at 0
  35           disk disk
  36           sizeof.disk = $
  37       end virtual
  38
  39
  40 fd0 disk            ; define fd0 data..
  41
  42 ;drv dd 0
  43 ;mov edi, drv+disk.boot
  44
  45      ;-----------------------------;
  46      ;   calculate root location   ;
  47      ;-----------------------------;
  48           xor     eax, eax
  49           mov     al, byte [fd0.boot.fats_per_drive]
  50           mul     word [fd0.boot.sectors_per_fat]
  51           add     ax, word [fd0.boot.reserved_sect]
  52           mov     [fd0.root_dir], ax
  53
  54 ;mov  si, [dsk]
  55 ;mov  ax, [si+disk.boot.sectorssize]
  56
  57
  58 init_fat12:
  59         push   eax
  60         ; a bit more code here
  61         pop    eax
  62         ret