kernel/fat12/fat12.asm

   1 ;----------------------------------------------------------;
   2 ; BOS kernel                Christoffer Bubach, 2012-2015. ;
   3 ;----------------------------------------------------------;
   4 ;                                                          ;
   5 ;    FAT12 driver.                                         ;
   6 ;                                                          ;
   7 ;----------------------------------------------------------;
   8
   9     ;---------------------------------------------;
  10     ;   FAT12 main info structure                 ;
  11     ;---------------------------------------------;
  12     struc fat12
  13     {
  14         .disk_number                     db  0       ; which VFS disk number
  15         .root_dir                        dw  0       ; position of rootdir
  16         .fat_1                           dd  0       ; position of fat1
  17         .fat_2                           dd  0       ; position of fat2
  18         .data_area                       dw  0       ; position of dataarea
  19         .disk_size                       dd  0       ; total storage size
  20         .free_space                      dd  0       ; free space available
  21         .boot                            bootsector
  22         .dir_entries:
  23             times 16 * sizeof.dir_entry  db 0        ; 512b dir entry buffer
  24         .fat_buffer:      times 512      db 0        ; 512b FAT cluster info buffer
  25     }
  26
  27     virtual at 0                                      ; could use "at esi" instead
  28         fat12 fat12
  29         sizeof.fat12 = $-$$
  30     end virtual
  31
  32     ;---------------------------------------------;
  33     ;   FAT12 bootsector structure                ;
  34     ;---------------------------------------------;
  35     struc bootsector                                  ; 512 bytes
  36     {
  37         .jumper            db  0,0,0
  38         .oem               db  0,0,0,0,0,0,0,0
  39         .sectorsize        dw  0
  40         .sect_per_clust    db  0
  41         .reserved_sect     dw  0                      ; reserved sectors, 1 for bootsector.
  42         .fats_per_drive    db  0
  43         .root_entries      dw  0
  44         .small_sectors     dw  0                      ; total sectors on small disk
  45         .media_describtor  db  0                      ; 240 / 0xF0 = 1.44MB, 3.5"
  46         .sectors_per_fat   dw  0                      ; 9   on 1.44MB, 3,5"
  47         .sect_per_track    dw  0                      ; 18  on 1.44MB, 3,5"
  48         .heads             dw  0                      ; 2   on 1.44MB, 3,5"
  49         .hidden_sectors    dd  0                      ; sectors before bootsector
  50         .large_sectors     dd  0                      ; total sectors if large disk
  51         .drive_no          db  0
  52         .reserved_field    db  0
  53         .bpb_signature     db  0                      ; 41=3 more (win NT req.), 0=end.
  54         .disk_id           dd  0                      ; random ident number on format.
  55         .volume_label      db  0,0,0,0,0,0,0,0,0,0,0
  56         .filesystem        db  0,0,0,0,0,0,0,0        ; "FAT12   " or "FAT16   "
  57         .code:   times 448 db  0
  58         .boot_signature    db  0,0                    ; 0x55,0xAA
  59     }
  60
  61     virtual at 0
  62         bootsector bootsector
  63         sizeof.bootsector = $-$$
  64     end virtual
  65
  66     ;---------------------------------------------;
  67     ;   FAT12 directory entry structure           ;
  68     ;---------------------------------------------;
  69     struc dir_entry
  70     {
  71         .filename          db  0,0,0,0,0,0,0,0
  72         .extension         db  0,0,0
  73         .attributes        db  0                      ; 0x10 = dir for example.
  74         .reserved          db  0,0,0,0,0,0,0,0,0,0
  75         .changed_time      dw  0
  76         .changed_date      dw  0
  77         .start_cluster     dw  0
  78         .filesize          dd  0
  79     }
  80
  81     virtual at 0
  82         dir_entry dir_entry
  83         sizeof.dir_entry = $-$$
  84     end virtual
  85
  86     ;---------------------------------------------;
  87     ;   FAT12 directory entry for LFN             ;
  88     ;---------------------------------------------;
  89     struc lfn_entry
  90     {
  91         .order             db  0                      ; LFN entry in sequence, never 0x00 or 0xE5.
  92         .namefirst         dw  0,0,0,0,0              ; 5 first unicode (2byte) chars
  93         .attribute         db  0                      ; 0x0F for Long File Name identification.
  94         .reserved          db  0
  95         .checksum          db  0                      ; 8.3 name checksum
  96         .namemiddle        dw  0,0,0,0,0,0            ; middle 6 unicode (2byte) chars
  97         .zero_cluster      dw  0                      ; always zero on LNF entries
  98         .namelast          dw  0,0                    ; last 2 unicode (2byte) characters.
  99     }
 100
 101     virtual at 0
 102         lfn_entry lfn_entry
 103         sizeof.lfn_entry = $-$$
 104     end virtual
 105
 106     ;------------------------------------------;
 107     ;   FAT cluster constants used             ;
 108     ;------------------------------------------;
 109     cluster_free        = 0x000                       ; up for grabs.
 110     cluster_reserved    = 0xFF0                       ; 0xFF0-0xFF6. 0xFF7=bad.
 111     cluster_last        = 0xFF8                       ; 0xFF8-0xFFF last cluster.
 112
 113     ;------------------------------------------;
 114     ;   Directory entry first char constants   ;
 115     ;------------------------------------------;
 116     entry_free          = 0xE5                        ; up for grabs.
 117     entry_last          = 0x00                        ; this and remaining is free
 118     entry_japan_kludge  = 0x0E                        ; should be outputed as 0xE5.
 119     entry_dot           = 0x2E                        ; ASCII dot, check for "." or ".." dirs
 120
 121     ;------------------------------------------;
 122     ;   Directory entry attribute masks        ;
 123     ;------------------------------------------;
 124     mask_readonly       = 0x01
 125     mask_hidden         = 0x02
 126     mask_system         = 0x04
 127     mask_volume_label   = 0x08
 128     mask_subdirectory   = 0x10
 129     mask_archive        = 0x20
 130
 131     ;------------------------------------------;
 132     ;   Long File Name entry constants         ;
 133     ;------------------------------------------;
 134     lfn_last_entry_mask = 0x40                         ; LFN sequence-order mask for last
 135     attribute_lfn       = 0x0F                         ; attrb. byte value for LFN dir entry
 136
 137
 138
 139
 140
 141 fd0 fat12            ; define fd0 data..  tmp example.
 142
 143 ; TODO, alloc memory for struct and keep pointer only.
 144 ; ---------------
 145 ;drive dd 0
 146 ;mov edi, drive+fat12into.boot
 147
 148 ;--------------------------------------------------------------;
 149 ;   init_fat12  -  detect if drive fs is fat12 and init        ;
 150 ;--------------------------------------------------------------;
 151 ;                                                              ;
 152 ;       in:  reg = pointer to VFS drive info                   ;
 153 ;                                                              ;
 154 ;       out: reg = pointer to struct(s) if FAT12 found         ;
 155 ;                                                              ;
 156 ;--------------------------------------------------------------;
 157 init_fat12:
 158         push   eax
 159         ;...
 160
 161      ;-----------------------------;
 162      ;   calculate root location   ;
 163      ;-----------------------------;
 164         xor    eax, eax
 165         mov    al, byte [fd0.boot.fats_per_drive]
 166         mul    word [fd0.boot.sectors_per_fat]
 167         add    ax, word [fd0.boot.reserved_sect]
 168         mov    [fd0.root_dir], ax
 169
 170 ;   working with
 171 ;mov  si, [drive]
 172 ;mov  ax, [si+fat12.boot.sectorssize]
 173
 174         ; a bit more code here
 175         pop    eax
 176         ret
 177
 178 ;--------------------------------------------------------------;
 179 ; calc_lfn_chksum   - get long file name checksum              ;
 180 ;--------------------------------------------------------------;
 181 ;                                                              ;
 182 ;          in:   esi = pointer to 11 byte 8.3 filename         ;
 183 ;                                                              ;
 184 ;          out:   ax = checksum                                ;
 185 ;                                                              ;
 186 ;--------------------------------------------------------------;
 187 calc_lfn_chksum:
 188         push   cx
 189         push   esi
 190
 191         mov    cx, 11
 192         xor    ax, ax                                 ; return value start with null
 193     .l1:
 194         push   cx
 195         movzx  cx, byte [esi]                         ; add next char to sum
 196         add    ax, cx
 197         pop    cx
 198         shr    ax, 1                                  ; shift sum right by 1
 199         inc    esi                                    ; prepare for next character
 200         loop   .l1
 201
 202         pop    esi
 203         pop    cx
 204         ret
 205
 206 ;--------------------------------------------------------------;
 207 ;   get_dir_entry  -  get a directory entry or amount          ;
 208 ;--------------------------------------------------------------;
 209 ;                                                              ;
 210 ;       in:  esi = pointer to prev dir entry or 0 for root     ;
 211 ;            cx  = entry no. to extract or 0 for none          ;
 212 ;                                                              ;
 213 ;       out: cx  = number of entries or unchanged if set       ;
 214 ;            edi = pointer to dir entry or unchanged if cx=0   ;
 215 ;--------------------------------------------------------------;
 216 get_dir_entry:
 217         ;......
 218         ret
 219
 220 ;--------------------------------------------------------------;
 221 ;   get_fat_entry  -  get a fat entry/cluster number           ;
 222 ;--------------------------------------------------------------;
 223 ;                                                              ;
 224 ;       in:  cx  = fat entry/cluster number                    ;
 225 ;                                                              ;
 226 ;       out: cx  = next fat entry/cluster no. or 0 if none     ;
 227 ;--------------------------------------------------------------;
 228 get_fat_entry:
 229         ;...
 230         ret
 231
 232 ;--------------------------------------------------------------;
 233 ;   get_cluster  -  get a cluster                              ;
 234 ;--------------------------------------------------------------;
 235 ;                                                              ;
 236 ;       in:  cx  = fat entry/cluster number                    ;
 237 ;                                                              ;
 238 ;       out: edi = pointer to cluster or zero if none          ;
 239 ;--------------------------------------------------------------;
 240 get_cluster:
 241         ;...
 242         ret