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: times sizeof.bootsector   db  0        ; copy of FAT12 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         .filehandles:
  26             times 32 * sizeof.filehandle db  0        ; for now, max opened files is 32
  27     }
  28
  29     virtual at 0                                      ; could use "at esi" instead
  30         fat12 fat12
  31         sizeof.fat12 = $-$$
  32     end virtual
  33
  34     ;---------------------------------------------;
  35     ;   FAT12 bootsector structure                ;
  36     ;---------------------------------------------;
  37     struc bootsector                                  ; 512 bytes
  38     {
  39         .jumper            db  0,0,0
  40         .oem               db  0,0,0,0,0,0,0,0
  41         .sectorsize        dw  0
  42         .sect_per_clust    db  0
  43         .reserved_sect     dw  0                      ; reserved sectors, 1 for bootsector.
  44         .fats_per_drive    db  0
  45         .root_entries      dw  0
  46         .small_sectors     dw  0                      ; total sectors on small disk
  47         .media_describtor  db  0                      ; 240 / 0xF0 = 1.44MB, 3.5"
  48         .sectors_per_fat   dw  0                      ; 9   on 1.44MB, 3,5"
  49         .sect_per_track    dw  0                      ; 18  on 1.44MB, 3,5"
  50         .heads             dw  0                      ; 2   on 1.44MB, 3,5"
  51         .hidden_sectors    dd  0                      ; sectors before bootsector
  52         .large_sectors     dd  0                      ; total sectors if large disk
  53         .drive_no          db  0
  54         .reserved_field    db  0
  55         .bpb_signature     db  0                      ; 41=3 more (win NT req.), 0=end.
  56         .disk_id           dd  0                      ; random ident number on format.
  57         .volume_label      db  0,0,0,0,0,0,0,0,0,0,0
  58         .filesystem        db  0,0,0,0,0,0,0,0        ; "FAT12   " or "FAT16   "
  59         .code:   times 448 db  0
  60         .boot_signature    db  0,0                    ; 0x55,0xAA
  61     }
  62
  63     virtual at 0
  64         bootsector bootsector
  65         sizeof.bootsector = $-$$
  66     end virtual
  67
  68     ;---------------------------------------------;
  69     ;   FAT12 directory entry structure           ;
  70     ;---------------------------------------------;
  71     struc dir_entry
  72     {
  73         .filename          db  0,0,0,0,0,0,0,0
  74         .extension         db  0,0,0
  75         .attributes        db  0                      ; 0x10 = dir for example.
  76         .reserved          db  0,0,0,0,0,0,0,0,0,0
  77         .changed_time      dw  0
  78         .changed_date      dw  0
  79         .start_cluster     dw  0
  80         .filesize          dd  0
  81     }
  82
  83     virtual at 0
  84         dir_entry dir_entry
  85         sizeof.dir_entry = $-$$
  86     end virtual
  87
  88     ;---------------------------------------------;
  89     ;   FAT12 directory entry for LFN             ;
  90     ;---------------------------------------------;
  91     struc lfn_entry
  92     {
  93         .order             db  0                      ; LFN entry in sequence, never 0x00 or 0xE5.
  94         .namefirst         dw  0,0,0,0,0              ; 5 first unicode (2byte) chars
  95         .attribute         db  0                      ; 0x0F for Long File Name identification.
  96         .reserved          db  0
  97         .checksum          db  0                      ; 8.3 name checksum
  98         .namemiddle        dw  0,0,0,0,0,0            ; middle 6 unicode (2byte) chars
  99         .zero_cluster      dw  0                      ; always zero on LNF entries
 100         .namelast          dw  0,0                    ; last 2 unicode (2byte) characters.
 101     }
 102
 103     virtual at 0
 104         lfn_entry lfn_entry
 105         sizeof.lfn_entry = $-$$
 106     end virtual
 107
 108     ;---------------------------------------------;
 109     ;   FAT12 file-handle structure               ;
 110     ;---------------------------------------------;
 111     struc filehandle
 112     {
 113         .handles           db  0                      ; reference count or or zero for unused
 114         .mode              db  0                      ; open mode. 0=read, 1=write, 2=r/w.
 115         .lfn_entry         dw  0                      ; file LFN directory entry position
 116         .direntry          dw  0                      ; file directory entry position
 117         .cluster           dw  0                      ; file first cluster
 118         .attribute         db  0                      ; file attributes
 119         .filetime          dw  0                      ; last modified time
 120         .filedate          dw  0                      ; last modified date
 121         .filesize          dd  0                      ; filesize
 122         .position          dd  0                      ; R/W position in file
 123         .clusterpos        dw  0                      ; cluster number of last cluster read
 124     }
 125
 126     virtual at 0
 127         filehandle filehandle
 128         sizeof.filehandle = $-$$
 129     end virtual
 130
 131     ;------------------------------------------;
 132     ;   FAT cluster constants used             ;
 133     ;------------------------------------------;
 134     cluster_free        = 0x000                       ; up for grabs.
 135     cluster_reserved    = 0xFF0                       ; 0xFF0-0xFF6. 0xFF7=bad.
 136     cluster_last        = 0xFF8                       ; 0xFF8-0xFFF last cluster.
 137
 138     ;------------------------------------------;
 139     ;   Directory entry first char constants   ;
 140     ;------------------------------------------;
 141     entry_free          = 0xE5                        ; up for grabs.
 142     entry_last          = 0x00                        ; this and remaining is free
 143     entry_japan_kludge  = 0x0E                        ; should be outputed as 0xE5.
 144     entry_dot           = 0x2E                        ; ASCII dot, check for "." or ".." dirs
 145
 146     ;------------------------------------------;
 147     ;   Directory entry attribute masks        ;
 148     ;------------------------------------------;
 149     mask_readonly       = 0x01
 150     mask_hidden         = 0x02
 151     mask_system         = 0x04
 152     mask_volume_label   = 0x08
 153     mask_subdirectory   = 0x10
 154     mask_archive        = 0x20
 155
 156     ;------------------------------------------;
 157     ;   Long File Name entry constants         ;
 158     ;------------------------------------------;
 159     lfn_last_entry_mask = 0x40                         ; LFN sequence-order mask for last
 160     attribute_lfn       = 0x0F                         ; attrb. byte value for LFN dir entry
 161
 162
 163
 164
 165
 166 fd0 fat12            ; define fd0 data..  tmp example.
 167
 168 ; TODO, alloc memory for struct and keep pointer only.
 169 ; ---------------
 170 ;drive dd 0
 171 ;mov edi, drive+fat12into.boot
 172
 173 ;--------------------------------------
 174 ; possible interface to copy/follow,
 175 ; add getFilename/path function?
 176 ;--------------------------------------
 177 ;    INT 21,3C  Create file using handle
 178 ;    INT 21,3D  Open file using handle
 179 ;    INT 21,3E  Close file using handle
 180 ;    INT 21,3F  Read file or device using handle
 181 ;    INT 21,40  Write file or device using handle
 182 ;    INT 21,41  Delete file
 183 ;    INT 21,42  Move file pointer using handle
 184 ;    INT 21,43  Change file mode
 185 ;    INT 21,45  Duplicate file handle
 186 ;    INT 21,46  Force duplicate file handle
 187 ;    INT 21,56  Rename file
 188 ;    INT 21,57  Get/set file date and time using handle
 189 ;    INT 21,5A  Create temporary file (3.x+)
 190 ;    INT 21,5B  Create new file (3.x+)
 191 ;    INT 21,67  Set handle count (DOS 3.3+)
 192
 193 ;--------------------------------------------------------------;
 194 ;   init_fat12  -  detect if drive fs is fat12 and init        ;
 195 ;--------------------------------------------------------------;
 196 ;                                                              ;
 197 ;       in:  reg = pointer to VFS drive info                   ;
 198 ;                                                              ;
 199 ;       out: reg = pointer to struct(s) if FAT12 found         ;
 200 ;                                                              ;
 201 ;--------------------------------------------------------------;
 202 init_fat12:
 203         push   eax
 204         ;...
 205
 206      ;-----------------------------;
 207      ;   calculate root location   ;
 208      ;-----------------------------;
 209         xor    eax, eax
 210         mov    al, byte [fd0.boot.fats_per_drive]
 211         mul    word [fd0.boot.sectors_per_fat]
 212         add    ax, word [fd0.boot.reserved_sect]
 213         mov    [fd0.root_dir], ax
 214
 215 ;   working with
 216 ;mov  si, [drive]
 217 ;mov  ax, [si+fat12.boot.sectorssize]
 218
 219         ; a bit more code here
 220         pop    eax
 221         ret
 222
 223 ;--------------------------------------------------------------;
 224 ; calc_lfn_chksum   - get long file name checksum              ;
 225 ;--------------------------------------------------------------;
 226 ;                                                              ;
 227 ;          in:   esi = pointer to 11 byte 8.3 filename         ;
 228 ;                                                              ;
 229 ;          out:   ax = checksum                                ;
 230 ;                                                              ;
 231 ;--------------------------------------------------------------;
 232 calc_lfn_chksum:
 233         push   cx
 234         push   esi
 235
 236         mov    cx, 11
 237         xor    ax, ax                                 ; return value start with null
 238     .l1:
 239         push   cx
 240         movzx  cx, byte [esi]                         ; add next char to sum
 241         add    ax, cx
 242         pop    cx
 243         shr    ax, 1                                  ; shift sum right by 1
 244         inc    esi                                    ; prepare for next character
 245         loop   .l1
 246
 247         pop    esi
 248         pop    cx
 249         ret
 250
 251 ;--------------------------------------------------------------;
 252 ;   get_dir_entry  -  get a directory entry or amount          ;
 253 ;--------------------------------------------------------------;
 254 ;                                                              ;
 255 ;       in:  esi = pointer to prev dir entry or 0 for root     ;
 256 ;            cx  = entry no. to extract or 0 for none          ;
 257 ;                                                              ;
 258 ;       out: cx  = number of entries or unchanged if set       ;
 259 ;            edi = pointer to dir entry or unchanged if cx=0   ;
 260 ;--------------------------------------------------------------;
 261 get_dir_entry:
 262         ;......
 263         ret
 264
 265 ;--------------------------------------------------------------;
 266 ;   get_fat_entry  -  get a fat entry/cluster number           ;
 267 ;--------------------------------------------------------------;
 268 ;                                                              ;
 269 ;       in:  cx  = fat entry/cluster number                    ;
 270 ;                                                              ;
 271 ;       out: cx  = next fat entry/cluster no. or 0 if none     ;
 272 ;--------------------------------------------------------------;
 273 get_fat_entry:
 274         ;...
 275         ret
 276
 277 ;--------------------------------------------------------------;
 278 ;   get_cluster  -  get a cluster                              ;
 279 ;--------------------------------------------------------------;
 280 ;                                                              ;
 281 ;       in:  cx  = fat entry/cluster number                    ;
 282 ;                                                              ;
 283 ;       out: edi = pointer to cluster or zero if none          ;
 284 ;--------------------------------------------------------------;
 285 get_cluster:
 286         ;...
 287         ret