kernel/fat12/fat12.asm

   1 ;----------------------------------------------------------;
   2 ; BOS kernel                Christoffer Bubach, 2012-2015. ;
   3 ;----------------------------------------------------------;
   4 ;                                                          ;
   5 ;    FAT12 driver.                                         ;
   6 ;                                                          ;
   7 ;----------------------------------------------------------;
   8
   9     ;---------------------------------------------;
  10     ;   FAT12 calltable and structure pointer     ;
  11     ;---------------------------------------------;
  12     FAT12:
  13         .data_pointer         dd  0                   ; internal driver data
  14         .FSname               db  'FAT12'             ; 5 char filesystem name
  15         .init                 dd  init_fat12          ; pointer to init
  16         .deinit               dd  0                   ; remove driver
  17         .format               dd  0                   ; format drive
  18         .mount                dd  0                   ; mount drive
  19         .unmount              dd  0                   ; unmount drive
  20         .find                 dd  0                   ; find file
  21         .findnext             dd  0                   ; get next match
  22         .open                 dd  0                   ; open file, get handle
  23         .close                dd  0                   ; close file from handle
  24         .attrib               dd  0                   ; get/set attrib. and time
  25         .read                 dd  0                   ; read file from handle
  26         .write                dd  0                   ; write file from handle
  27         .seek                 dd  0                   ; seek from handle
  28         .rename               dd  0                   ; rename file
  29         .remove               dd  0                   ; remove file/dir
  30         .create               dd  0                   ; create file/dir
  31         .ioctl                dd  0                   ; extra calls if exists
  32
  33     ;---------------------------------------------;
  34     ;   FAT12 main info structure                 ;
  35     ;---------------------------------------------;
  36     struc fat12_data
  37     {
  38         .disk_number                     db  0        ; which VFS disk number
  39         .root_dir                        dw  0        ; position of rootdir
  40         .disk_size                       dd  0        ; total storage size
  41         .free_space                      dd  0        ; free space available
  42         .fat_1                           dd  0        ; position of fat1
  43         .fat_2                           dd  0        ; position of fat2
  44         .data_area                       dw  0        ; position of dataarea
  45         .boot: times sizeof.bootsector   db  0        ; copy of FAT12 bootsector
  46         .dir_entries:
  47             times 16 * sizeof.dir_entry  db  0        ; 512b dir entry buffer
  48         .fat_buffer:      times 512      db  0        ; 512b FAT cluster info buffer
  49         .foundfile:
  50             times 1 * sizeof.search      db  0        ; "DTA" like structure
  51         .filehandles:                                 ; "System File Table"
  52             times 32 * sizeof.filehandle db  0        ; for now, max opened files is 32
  53     }
  54
  55     virtual at 0                                      ; could use "at esi" instead
  56         fat12_data fat12_data
  57         sizeof.fat12_data = $-$$
  58     end virtual
  59
  60     ;---------------------------------------------;
  61     ;   FAT12 bootsector structure                ;
  62     ;---------------------------------------------;
  63     struc bootsector                                  ; 512 bytes
  64     {
  65         .jumper            db  0,0,0
  66         .oem               db  0,0,0,0,0,0,0,0
  67         .sectorsize        dw  0
  68         .sect_per_clust    db  0
  69         .reserved_sect     dw  0                      ; reserved sectors, 1 for bootsector.
  70         .fats_per_drive    db  0
  71         .root_entries      dw  0
  72         .small_sectors     dw  0                      ; total sectors on small disk
  73         .media_describtor  db  0                      ; 240 / 0xF0 = 1.44MB, 3.5"
  74         .sectors_per_fat   dw  0                      ; 9   on 1.44MB, 3,5"
  75         .sect_per_track    dw  0                      ; 18  on 1.44MB, 3,5"
  76         .heads             dw  0                      ; 2   on 1.44MB, 3,5"
  77         .hidden_sectors    dd  0                      ; sectors before bootsector
  78         .large_sectors     dd  0                      ; total sectors if large disk
  79         .drive_no          db  0
  80         .reserved_field    db  0
  81         .bpb_signature     db  0                      ; 41=3 more (win NT req.), 0=end.
  82         .disk_id           dd  0                      ; random ident number on format.
  83         .volume_label      db  0,0,0,0,0,0,0,0,0,0,0
  84         .filesystem        db  0,0,0,0,0,0,0,0        ; "FAT12   " or "FAT16   "
  85         .code:   times 448 db  0
  86         .boot_signature    db  0,0                    ; 0x55,0xAA
  87     }
  88
  89     virtual at 0
  90         bootsector bootsector
  91         sizeof.bootsector = $-$$
  92     end virtual
  93
  94     ;---------------------------------------------;
  95     ;   FAT12 directory entry structure           ;
  96     ;---------------------------------------------;
  97     struc dir_entry
  98     {
  99         .filename          db  0,0,0,0,0,0,0,0
 100         .extension         db  0,0,0
 101         .attributes        db  0                      ; 0x10 = dir for example.
 102         .reserved          db  0,0,0,0,0,0,0,0,0,0
 103         .changed_time      dw  0
 104         .changed_date      dw  0
 105         .start_cluster     dw  0
 106         .filesize          dd  0
 107     }
 108
 109     virtual at 0
 110         dir_entry dir_entry
 111         sizeof.dir_entry = $-$$
 112     end virtual
 113
 114     ;---------------------------------------------;
 115     ;   FAT12 directory entry for LFN             ;
 116     ;---------------------------------------------;
 117     struc lfn_entry
 118     {
 119         .order             db  0                      ; LFN entry in sequence, never 0x00 or 0xE5.
 120         .namefirst         dw  0,0,0,0,0              ; 5 first unicode (2byte) chars
 121         .attribute         db  0                      ; 0x0F for Long File Name identification.
 122         .reserved          db  0
 123         .checksum          db  0                      ; 8.3 name checksum
 124         .namemiddle        dw  0,0,0,0,0,0            ; middle 6 unicode (2byte) chars
 125         .zero_cluster      dw  0                      ; always zero on LNF entries
 126         .namelast          dw  0,0                    ; last 2 unicode (2byte) characters.
 127     }
 128
 129     virtual at 0
 130         lfn_entry lfn_entry
 131         sizeof.lfn_entry = $-$$
 132     end virtual
 133
 134     ;---------------------------------------------;
 135     ;   FAT12 file search/DTA structure           ;
 136     ;---------------------------------------------;
 137     struc search
 138     {
 139         .searchname:
 140             times 255      db  0                      ; file search pattern.
 141         .attribute         db  0                      ; search attribute.
 142         .direntry          dw  0                      ; directory entry number, 0 based
 143         .dircluster        dw  0                      ; starting cluster of dir, 0 root
 144         .foundattrib       db  0                      ; attribute of matching file
 145         .foundtime         dw  0                      ; file time
 146         .founddate         dw  0                      ; file date
 147         .foundsize         dw  0                      ; file size
 148     }
 149
 150     virtual at 0
 151         search search
 152         sizeof.search = $-$$
 153     end virtual
 154
 155     ;---------------------------------------------;
 156     ;   FAT12 file-handle structure               ;
 157     ;---------------------------------------------;
 158     struc filehandle
 159     {
 160         .handles           db  0                      ; reference count or or zero for unused
 161         .mode              db  0                      ; open mode. 0=read, 1=write, 2=r/w.
 162         .lfn_entry         dw  0                      ; file LFN directory entry position
 163         .direntry          dw  0                      ; file directory entry position
 164         .cluster           dw  0                      ; file first cluster
 165         .attribute         db  0                      ; file attributes
 166         .filetime          dw  0                      ; last modified time
 167         .filedate          dw  0                      ; last modified date
 168         .filesize          dd  0                      ; filesize
 169         .position          dd  0                      ; R/W position in file
 170         .clusterpos        dw  0                      ; cluster number of last cluster read
 171         .shortname:
 172             times 11       db  0                      ; short name
 173         .fullname:
 174             times 255      db  0                      ; the full LFN
 175     }
 176
 177     virtual at 0
 178         filehandle filehandle
 179         sizeof.filehandle = $-$$
 180     end virtual
 181
 182     ;------------------------------------------;
 183     ;   FAT cluster constants used             ;
 184     ;------------------------------------------;
 185     cluster_free        = 0x000                       ; up for grabs.
 186     cluster_reserved    = 0xFF0                       ; 0xFF0-0xFF6. 0xFF7=bad.
 187     cluster_last        = 0xFF8                       ; 0xFF8-0xFFF last cluster.
 188
 189     ;------------------------------------------;
 190     ;   Directory entry first char constants   ;
 191     ;------------------------------------------;
 192     entry_free          = 0xE5                        ; up for grabs.
 193     entry_last          = 0x00                        ; this and remaining is free
 194     entry_japan_kludge  = 0x0E                        ; should be outputed as 0xE5.
 195     entry_dot           = 0x2E                        ; ASCII dot, check for "." or ".." dirs
 196
 197     ;------------------------------------------;
 198     ;   Directory entry attribute masks        ;
 199     ;------------------------------------------;
 200     mask_readonly       = 0x01
 201     mask_hidden         = 0x02
 202     mask_system         = 0x04
 203     mask_volume_label   = 0x08
 204     mask_subdirectory   = 0x10
 205     mask_archive        = 0x20
 206
 207     ;------------------------------------------;
 208     ;   Long File Name entry constants         ;
 209     ;------------------------------------------;
 210     lfn_last_entry_mask = 0x40                         ; LFN sequence-order mask for last
 211     attribute_lfn       = 0x0F                         ; attrb. byte value for LFN dir entry
 212
 213
 214 ;--------------------------------------------------------------;
 215 ;   init_fat12  -  detect if drive fs is fat12 and init        ;
 216 ;--------------------------------------------------------------;
 217 ;                                                              ;
 218 ;       in:  reg = pointer to VFS drive info                   ;
 219 ;                                                              ;
 220 ;       out: reg = pointer to struct(s) if FAT12 found         ;
 221 ;                                                              ;
 222 ;--------------------------------------------------------------;
 223 init_fat12:
 224         push   eax
 225         ;...
 226
 227      ;-----------------------------;
 228      ;   calculate root location   ;
 229      ;-----------------------------;
 230         xor    eax, eax
 231         mov    al, byte [fd0.boot.fats_per_drive]
 232         mul    word [fd0.boot.sectors_per_fat]
 233         add    ax, word [fd0.boot.reserved_sect]
 234         mov    [fd0.root_dir], ax
 235
 236 ;   working with
 237 ;mov  si, [drive]
 238 ;mov  ax, [si+fat12.boot.sectorssize]
 239
 240         ; a bit more code here
 241         pop    eax
 242         ret
 243
 244 ;--------------------------------------------------------------;
 245 ; calc_lfn_chksum   - get long file name checksum              ;
 246 ;--------------------------------------------------------------;
 247 ;                                                              ;
 248 ;          in:   esi = pointer to 11 byte 8.3 filename         ;
 249 ;                                                              ;
 250 ;          out:   ax = checksum                                ;
 251 ;                                                              ;
 252 ;--------------------------------------------------------------;
 253 calc_lfn_chksum:
 254         push   cx
 255         push   esi
 256
 257         mov    cx, 11
 258         xor    ax, ax                                 ; return value start with null
 259     .l1:
 260         push   cx
 261         movzx  cx, byte [esi]                         ; add next char to sum
 262         add    ax, cx
 263         pop    cx
 264         shr    ax, 1                                  ; shift sum right by 1
 265         inc    esi                                    ; prepare for next character
 266         loop   .l1
 267
 268         pop    esi
 269         pop    cx
 270         ret
 271
 272 ;--------------------------------------------------------------;
 273 ;   get_dir_entry  -  get a directory entry or amount          ;
 274 ;--------------------------------------------------------------;
 275 ;                                                              ;
 276 ;       in:  esi = pointer to prev dir entry or 0 for root     ;
 277 ;            cx  = entry no. to extract or 0 for none          ;
 278 ;                                                              ;
 279 ;       out: cx  = number of entries or unchanged if set       ;
 280 ;            edi = pointer to dir entry or unchanged if cx=0   ;
 281 ;--------------------------------------------------------------;
 282 get_dir_entry:
 283         ;......
 284         ret
 285
 286 ;--------------------------------------------------------------;
 287 ;   get_fat_entry  -  get a fat entry/cluster number           ;
 288 ;--------------------------------------------------------------;
 289 ;                                                              ;
 290 ;       in:  cx  = fat entry/cluster number                    ;
 291 ;                                                              ;
 292 ;       out: cx  = next fat entry/cluster no. or 0 if none     ;
 293 ;--------------------------------------------------------------;
 294 get_fat_entry:
 295         ;...
 296         ret
 297
 298 ;--------------------------------------------------------------;
 299 ;   get_cluster  -  get a cluster                              ;
 300 ;--------------------------------------------------------------;
 301 ;                                                              ;
 302 ;       in:  cx  = fat entry/cluster number                    ;
 303 ;                                                              ;
 304 ;       out: edi = pointer to cluster or zero if none          ;
 305 ;--------------------------------------------------------------;
 306 get_cluster:
 307         ;...
 308         ret