1 ; **************************************************************************** 2 ; TRDOS386.ASM (TRDOS 386 Kernel) - v2.0.0 - fat12_bs.s - FAT12 BOOT SECTOR 3 ; ---------------------------------------------------------------------------- 4 ; Last Update: 26/12/2017 5 ; ---------------------------------------------------------------------------- 6 ; Beginning: 24/12/2017 7 ; ---------------------------------------------------------------------------- 8 ; Assembler: NASM version 2.11 9 ; ---------------------------------------------------------------------------- 10 ; ((nasm fat12_bs.s -l fat12_bs.lst -o FAT12_BS.BIN)) 11 ; ---------------------------------------------------------------------------- 12 ; Turkish Rational DOS 13 ; Operating System Project v2.0 by ERDOGAN TAN (Beginning: 04/01/2016) 14 ; 15 ; NOTE: This code has some tricks and TRDOS 386 specific modifications 16 ; which are not a part of original Microsoft Windows (XP) FAT12 BS code. 17 ; (Purpose of TRDOS 386 specific modifications and tricks is to load 18 ; 'TRDOS386.SYS' kernel file as easy and as correct, without affecting 19 ; FAT12 FS recognization for other operating systems.) 20 ; 21 ; Derived from Microsoft WINDOWS XP FAT (FAT16&FAT12) boot sector code 22 ; which is edited/disassembled by Erdogan Tan (17/12/2017), 23 ; by using BINFILEHEX (Erdogan Tan) & IDA PRO FREE (Hex-Rays SA) programs. 24 ; 25 ; Derived from 'fat16_bs.s' TRDOS 386 FAT16 boot sector source code 26 ; by Erdogan Tan (24/12/2017). 27 ; **************************************************************************** 28 ; incbin "FAT12_BS.BIN" (in 'hdimage.s' & 'hdformat.s') 29 30 rts_segment equ 1000h 31 32 [BITS 16] 33 [ORG 7C00h] 34 BS_jmpBoot: 35 00000000 EB3C jmp short loc_3E ; jmp short start 36 BS_jmpBoot_nop: 37 00000002 90 nop 38 39 ; BootSector Identification (Data) Block 40 BS_OEMName: 41 00000003 4D53444F53352E30 db 'MSDOS5.0' ; bp+3 42 0000000B 0002 BPB_BytesPerSec: dw 512 ; bp+11 43 0000000D 08 BPB_SecPerClus: db 8 ; bp+13 44 0000000E 0100 BPB_RsvdSecCnt: dw 1 ; bp+14 45 00000010 02 BPB_NumFATs: db 2 ; bp+16 46 00000011 0002 BPB_RootEntCnt: dw 512 ; bp+17 47 00000013 0000 BPB_TotSec16: dw 0 ; bp+19 48 00000015 F8 BPB_Media: db 0F8h ; bp+21 49 00000016 0000 BPB_FATSz16: dw 0 ; bp+22 50 00000018 3F00 BPB_SecPerTrk: dw 63 ; bp+24 51 0000001A 1000 BPB_NumHeads: dw 16 ; bp+26 52 0000001C 01000000 BPB_HiddSec: dd 1 ; bp+28 53 00000020 00000000 BPB_TotSec32: dd 0 ; bp+32 54 00000024 80 BS_DrvNum: db 80h ; bp+36 55 00000025 00 BS_Reserved1: db 0 ; bp+37 56 00000026 29 BS_BootSig: db 29h ; bp+38 57 00000027 00000000 BS_VolID: dd 0 ; bp+39 58 0000002B 5452444F5333383620- BS_VolLab: db 'TRDOS386 ' ; bp+43 58 00000034 2020 59 00000036 4641543132202020 BS_FilSysType: db 'FAT12 ' ; bp+54 60 61 start: 62 loc_3E: 63 0000003E 01FF add di, di ; db 01h, 0FFh -> FAT 12 64 ; TRDOS 386 (FAT12 BS) identifier/trick! 65 66 00000040 BD007C mov bp, 7C00h 67 68 00000043 3DA101 cmp ax, 417 ; If AX=417, the masterboot sector 69 ; has a SINGLIX FS (& TRDOS 386) 70 ; masterboot code; and... 71 ; DX=ES=SS=0, BP=7C00h 72 ; SP=7C00h ... masterboot sector has 73 ; been loaded at 0:600h, it has 74 ; CHS parameters at offset 600h+420. 75 ; (There is a 01A1h in offset 600h+417) 76 77 00000046 740D je short bs_01 ; no need to following assignments ! 78 79 ;xor ax, ax 80 ;mov ds, ax 81 ;mov es, ax 82 00000048 0E push cs 83 00000049 1F pop ds 84 0000004A 1E push ds 85 0000004B 07 pop es 86 0000004C FA cli 87 ;mov ss, ax 88 ;mov sp, bp 89 0000004D 0E push cs 90 0000004E 17 pop ss 91 0000004F 89EC mov sp, bp 92 00000051 FB sti 93 00000052 8A5624 mov dl, [bp+24h] ; [BS_DrvNum] 94 bs_01: 95 00000055 8936[FC01] mov [bsReserved1], si ; Partition entry address.. 96 ; (from Singlix FS MBR) 97 ; (7BEh,7CEh,7DEh,7EEh) 98 99 ; Check Bytes/Sector value 100 ; It must be 512 !? (at least, for TRDOS386) 101 ;cmp word [bp+0Bh], 512 ; [BPB_BytesPerSec] 102 ;cmp byte [bp+0Ch], 2 103 ;jne short invalid_system_disk 104 105 ; Check Extended Boot Signature (It must be 29h) 106 ;cmp byte [bp+26h], 29h ; [BS_BootSig] 107 ;jne short invalid_system_disk 108 109 ; overwrite hd drive number ! 110 ;mov [BS_DrvNum], dl ; drive number from INT 19h 111 00000059 885624 mov [bp+24h], dl 112 ;mov [bp+25h], dh ; [BS_Reserved1] = Partition ID !!! 113 ;mov [bp+24h], dx 114 115 ; reset address pointers and set SP 116 ;xor cx, cx ; 0 117 ;push cx ; [bp-2] ; Cluster 2 address (high word) 118 ;push cx ; [bp-4] ; Cluster 2 address (low word) 119 ;push cx ; [bp-6] ; FAT (0) address (high word) 120 ;push cx ; [bp-8] ; FAT (0) address (low word) 121 0000005C 83EC08 sub sp, 8 122 ;dec cx ; 0FFFFh 123 ;push cx ; [bp-10] ; FAT sector buffer address reset (-1) 124 ;inc cx ; 0 125 0000005F 6AFF push 0FFFFh 126 00000061 680010 push rts_segment ; Kernel loading segment in 7BF4h 127 128 ; SP = 7BF4h 129 130 ; calculate cluster 2 address 131 00000064 31C9 xor cx, cx 132 00000066 8B461C mov ax, [bp+1Ch] ; word [BPB_HiddSec] 133 00000069 8B561E mov dx, [bp+1Eh] ; word [BPB_HiddSec+2] 134 0000006C 03460E add ax, [bp+0Eh] ; [BPB_RsvdSecCnt] 135 0000006F 11CA adc dx, cx ; 0 136 137 00000071 8946F8 mov [bp-8], ax ; FAT beginning sector (lw) 138 00000074 8956FA mov [bp-6], dx ; FAT beginning sector (hw) 139 140 00000077 8A4610 mov al, [bp+10h] ; [BPB_NumFATs] 141 0000007A 98 cbw 142 0000007B F76616 mul word [bp+16h] ; [BPB_FATSz16] 143 144 0000007E 0346F8 add ax, [bp-8] 145 00000081 1356FA adc dx, [bp-6] 146 147 00000084 8B7611 mov si, [bp+11h] ; [BPB_RootEntCnt] 148 00000087 BB0002 mov bx, 512 149 0000008A 60 pusha 150 0000008B 8946FC mov [bp-4], ax ; [7BFCh] = Root Dir address 151 0000008E 8956FE mov [bp-2], dx 152 00000091 B82000 mov ax, 20h ; 32 ; Directory Entry Size 153 00000094 F7E6 mul si 154 ;mov bx, [bp+0Bh] ; [BPB_BytesPerSec] = 512 155 ;mov bx, 512 156 00000096 01D8 add ax, bx 157 00000098 48 dec ax 158 00000099 F7F3 div bx 159 ; AX = Root directory sectors 160 0000009B 0146FC add [bp-4], ax ; [7BFCh] = Start of Data area 161 0000009E 114EFE adc [bp-2], cx ; adc [bp-2], 0 162 ;popa 163 164 ;; check for ROMBIOS INT 13h extensions 165 ;mov ah, 41h 166 ;mov bx, 55AAh 167 ;;mov dl, [BS_DrvNum] 168 ;;mov dl, [bp+40h] 169 ;int 13h 170 ;jc short bs_02 171 ;cmp bx, 0AA55h 172 ;jne short bs_02 173 ;test cl, 1 174 ;jz short bs_02 175 176 ; ROMBIOS INT 13h extentions are present... 177 178 ;;mov al, [loc_3E] 179 ;mov al, [bp+62] 180 ;;mov [BS_jmpBoot+2], al ; 'LBA mode is available' 181 ;mov [bp+2], al ; 0Eh (LBA) or 06h (CHS) or 04h (CHS) 182 bs_02: 183 000000A1 61 popa 184 000000A2 EB07 jmp short load_root_dir_sector 185 186 check_next_dir_entry: 187 000000A4 83C720 add di, 32 ; next dir entry 188 000000A7 39DF cmp di, bx ; end of root dir buffer 189 000000A9 7209 jb short search_startup_file 190 191 load_root_dir_sector: 192 ; load root directory and check directory entries 193 ; 25/12/2017 194 ;mov bx, 7E00h ; Root dir buffer (1 sector) 195 000000AB B77E mov bh, 7Eh 196 000000AD 89DF mov di, bx ; Root dir entry offset 197 ; DX_AX = root dir sector address (DX = 0) 198 ;mov cl, 1 199 000000AF E8BD00 call Read1Sector ; Read 1 sector (CL=1) 200 000000B2 721E jc short disk_io_error 201 202 ; BX = 8000h 203 search_startup_file: 204 ; check/compare root dir entry for/with kernel file 205 000000B4 382D cmp [di], ch ; 0 206 000000B6 740E je invalid_system_disk ; kernel not found! 207 000000B8 60 pusha 208 000000B9 B10B mov cl, 11 ; 0Bh 209 000000BB BE[F001] mov si, rtsfilename ; Run Time System file name 210 ; or Kernel file name 211 ; (or Startup file name) 212 ; (or Standalone file name) 213 ; in MSDOS directory entry 214 ; format. ('TRDOS386SYS') 215 ; It is 'TRDOS386.SYS' 216 ; for TRDOS 386 OS. 217 000000BE F3A6 repe cmpsb ; compare dir entry and kernel's name 218 000000C0 61 popa 219 000000C1 7414 jz short load_startup_file ; kernel is there! 220 000000C3 4E dec si ; countdown from Root dir entry count 221 000000C4 75DE jnz short check_next_dir_entry 222 223 invalid_system_disk: 224 ; 'Replace Disk & Press Any Key' message (24/12/2017) 225 000000C6 BE[BE01] mov si, Inv_disk_Msg 226 write_disk_io_err_msg: 227 000000C9 E89500 call print_msg 228 getchar_reboot: 229 ; Wait for a keystroke just before reboot 230 000000CC 30E4 xor ah, ah 231 000000CE CD16 int 16h 232 233 000000D0 CD19 int 19h ; disk boot 234 ; causes reboot of disk system 235 disk_io_error: 236 000000D2 BE[B101] mov si, Diskio_err_Msg 237 ;call print_msg 238 000000D5 EBF2 jmp short write_disk_io_err_msg ; 24/12/2017 239 ;replace_disk: 240 ; mov si, Replace_Msg 241 ;replace_disk: 242 ; mov si, Disk_err_replace_Msg 243 ; call print_msg 244 ; jmp short getchar_reboot 245 246 load_startup_file: 247 ; DI = directory entry offset 248 ; Get the First Cluster (Dir entry offset 26) 249 000000D7 8B451A mov ax, [di+1Ah] ; [di+DIR_FstClusLO] 250 ReadCluster: 251 000000DA 50 push ax ; cluster number 252 253 000000DB 48 dec ax 254 000000DC 48 dec ax ; cluster number - 2 255 256 ;xor ch, ch 257 000000DD 8A4E0D mov cl, [bp+0Dh] ; [BPB_SecPerClus] 258 000000E0 F7E1 mul cx 259 260 000000E2 0346FC add ax, [bp-4] ; [7CFCh], Start of FAT FS data area 261 000000E5 1356FE adc dx, [bp-2] 262 263 ;mov bx, [next_segment] 264 000000E8 8B5EF4 mov bx, [bp-12] ; Kernel loading segment (in 7BF4h) 265 000000EB 06 push es 266 000000EC 8EC3 mov es, bx ; segment = 1000h + 267 000000EE 31DB xor bx, bx ; offset = 0 268 ; CL = num of sectors to read (= sectors/cluster) 269 000000F0 E87E00 call ReadSector 270 000000F3 07 pop es 271 000000F4 58 pop ax ; cluster number 272 000000F5 72DB jc short disk_io_error 273 000000F7 C1EB04 shr bx, 4 ; from byte count to paragraph count 274 ;add [next_segment], bx 275 000000FA 015EF4 add [bp-12], bx ; Next segment (in 7BF4h) 276 277 ;call get_next_cluster 278 ;jc short disk_io_error 279 280 get_next_cluster: ; get next (FAT12) file cluster 281 ; AX = current cluster number 282 ;call get_fat12_entry 283 ;jc short disk_io_error 284 285 get_fat12_entry: 286 ; AX = 12 bit cluster number 287 000000FD 50 push ax ; * 288 000000FE B90300 mov cx, 3 ; 1 cluster = 3/2 bytes 289 00000101 F7E1 mul cx 290 00000103 D1E8 shr ax, 1 291 292 ; AX = byte offset in FAT 293 00000105 BB0006 mov bx, 512*3 ; 3 sectors 294 ;xor dx, dx 295 00000108 F7F3 div bx 296 0000010A 89D3 mov bx, dx ; offset (0 to 1534) 297 0000010C F7E1 mul cx ; *3 (0,3,6,9) 298 ; AX = FAT sector number (as offset) 299 ; (the 1st sector of 3 sectors 300 ; in the FAT buffer) 301 302 0000010E BF0080 mov di, 8000h ; FAT buffer address 303 ; (8000h to 8600h) 304 ; AX = FAT sector number (relative) 305 ; Check FAT sector number if it is already 306 ; in FAT buffer at 8000h. 307 ; Current FAT sector is in 7BF6h. 308 ; (Note: initial FAT sector value in 7BF6h is 309 ; 0FFFFh which means the buff is not loaded yet.) 310 00000111 3B46F6 cmp ax, [bp-10] ; [7BF6h] 311 00000114 7416 je short bs_03 ; same sector in FAT buffer 312 00000116 8946F6 mov [bp-10], ax ; save FAT sector number 313 314 00000119 53 push bx ; ** ; 0 to 1534 (clust entry offset) 315 316 ; Calculate absolute (LBA) address of FAT sector 317 ; by adding hidden (partition's start sector) 318 ; and reserved sectors (between BS and FAT). 319 ; (Note: FAT copy 0 address is stored in 7BF8h) 320 0000011A 31D2 xor dx, dx 321 0000011C 0346F8 add ax, [bp-8] ; FAT (0) sector addr (lw) 322 0000011F 1356FA adc dx, [bp-6] ; FAT (0) sector addr (hw) 323 324 ;push bx 325 00000122 89FB mov bx, di 326 ; 24/12/2017 327 ; Load 3 consecutive sectors into FAT buffer 328 ;mov cx, 3 329 00000124 E84A00 call ReadSector 330 ; If cf = 1 -> Disk I/O err, not invalid sys disk! 331 00000127 5B pop bx ; ** ; FAT buffer entry offset (0-1534) 332 00000128 5A pop dx ; * ; Cluster number 333 00000129 72A7 jc short disk_io_error 334 ; 25/12/2017 335 0000012B 52 push dx ; * 336 ;jmp short end_of_get_fat12_entry 337 bs_03: 338 0000012C 5A pop dx ; * 339 ; retn 340 341 end_of_get_fat12_entry: 342 0000012D 8B01 mov ax, [bx+di] ; 16 bit cluster number 343 344 ; If current cluster number is odd number .. 345 0000012F 80E201 and dl, 1 ; * 346 00000132 7403 jz short bs_04 ; even cluster number 347 ; .. shift next cluster number to 4 bits right 348 00000134 C1E804 shr ax, 4 349 bs_04: 350 00000137 25FF0F and ax, 0FFFh 351 ;and ah, 0Fh 352 ;;cmp ax, 0FF7h 353 ;;cmc 354 ;; retn 355 356 end_of_get_next_cluster: 357 ; 24/12/2017 358 0000013A 83F802 cmp ax, 2 359 0000013D 7287 jb short invalid_system_disk 360 361 0000013F 3DF70F cmp ax, 0FF7h 362 ;jnb short bs_05 ; Startup file has been loaded. 363 00000142 7296 jb short ReadCluster ; load/read next cluster 364 365 end_of_ReadCluster: 366 bs_05: 367 ; Set TRDOS 386 kernel specific parameters (& signs) 368 ; and 369 ; Launch TRDOS 386 Kernel (Startup/RTS file) 370 371 ;mov dl, [BS_DrvNum] 372 00000144 8B5624 mov dx, [bp+24h] ; DL = Drive number, DH = 0 373 00000147 FEC6 inc dh ; TRDOS 386 FAT12 BS major version = 1 374 375 ;mov ax, [next_segment] ; 16 paragraphs after the 376 ; start of the last segment 377 ; of the kernel file loading 378 ; space. 379 ; So, (top of) stack will have 380 ; 256 bytes or more distance 381 ; from the last byte 382 ; of the kernel file. 383 ; (This will be enough for 384 ; TRDOS 386 kernel before 385 ; entering protected mode.) 386 387 00000149 8B46F4 mov ax, [bp-12] ; [7BF4h] ; the last segment 388 ; which is the kernel file 389 ; has been loaded in. 390 0000014C FA cli 391 0000014D 8ED0 mov ss, ax 392 0000014F BCFEFF mov sp, 0FFFEh 393 00000152 FB sti 394 395 00000153 BB0010 mov bx, rts_segment ; 1000h 396 00000156 8EDB mov ds, bx 397 00000158 8EC3 mov es, bx 398 399 ; bp = 7C00h 400 401 0000015A B8A101 mov ax, 417 ; TRDOS boot sector sign for TRDOS386.SYS 402 403 ;jmp rts_segment:0 404 405 0000015D 06 push es 406 0000015E 6A00 push 0 407 00000160 CB retf 408 409 print_msg: 410 ; DS:SI = Error message address (ASCIIZ string) 411 00000161 B40E mov ah, 0Eh 412 00000163 BB0700 mov bx, 7 413 bs_06: 414 00000166 AC lodsb 415 00000167 84C0 test al, al 416 ;jz short bs_07 417 00000169 743D jz short bs_09 418 0000016B CD10 int 10h 419 0000016D EBF7 jmp short bs_06 420 bs_07: 421 ; retn 422 423 Read1Sector: ; 25/12/2017 424 0000016F B101 mov cl, 1 425 ReadSector: 426 00000171 B504 mov ch, 4 ; retry count 427 ReadSector_retry: 428 00000173 60 pusha 429 00000174 91 xchg ax, cx 430 00000175 8B4618 mov ax, [bp+18h] ; [BPB_SecPerTrk] 431 00000178 96 xchg ax, si 432 00000179 92 xchg ax, dx 433 0000017A 31D2 xor dx, dx 434 0000017C F7F6 div si 435 0000017E 91 xchg ax, cx 436 0000017F F7F6 div si 437 00000181 42 inc dx 438 00000182 87CA xchg cx, dx 439 00000184 F7761A div word [bp+1Ah] ; [BPB_NumHeads] 440 00000187 88D6 mov dh, dl 441 00000189 88C5 mov ch, al 442 0000018B C0CC02 ror ah, 2 443 0000018E 08E1 or cl, ah 444 445 00000190 B80102 mov ax, 201h 446 00000193 8A5624 mov dl, [bp+24h] ; [BS_DrvNum] 447 00000196 CD13 int 13h ; DISK - read 448 00000198 61 popa 449 00000199 720E jc short bs_10 ; return with error 450 451 0000019B 40 inc ax 452 0000019C 7501 jnz short bs_08 453 0000019E 42 inc dx 454 bs_08: 455 ;add bx, [bp+0Bh] ; [BPB_BytesPerSec] = 512 456 ;add bx, 512 457 0000019F 80C702 add bh, 2 458 ;dec cx 459 000001A2 FEC9 dec cl 460 000001A4 75CB jnz short ReadSector 461 ;clc 462 000001A6 30ED xor ch, ch 463 bs_09: 464 000001A8 C3 retn 465 bs_10: 466 000001A9 FECD dec ch 467 000001AB 75C6 jnz short ReadSector_retry 468 000001AD C3 retn 469 470 ;next_segment: 471 ; dw rts_segment 472 473 000001AE 04 db 04 474 000001AF 01 db 01 475 000001B0 07 db 07h ; filler 476 477 Diskio_err_Msg: 478 000001B1 0D0A db 0Dh, 0Ah 479 000001B3 4469736B206572726F- db 'Disk error!' 479 000001BC 7221 480 ;db 0 481 Inv_disk_Msg: 482 ; db 0Dh, 0Ah 483 ; db 'Invalid system disk' 484 ;Disk_err_replace_Msg: 485 ; db '!' 486 Replace_Msg: 487 000001BE 0D0A db 0Dh, 0Ah 488 000001C0 5265706C6163652074- db 'Replace the disk and press any key to reboot.' 488 000001C9 6865206469736B2061- 488 000001D2 6E6420707265737320- 488 000001DB 616E79206B65792074- 488 000001E4 6F207265626F6F742E 489 000001ED 0D0A00 db 0Dh, 0Ah, 0 490 491 ;times (508+rtsfilename-bsReserved1) - ($ - $$) db 0 492 rtsfilename: 493 000001F0 5452444F5333383653- db 'TRDOS386SYS' 493 000001F9 5953 494 000001FB 00 db 0 495 next_segment: 496 ;org 7C00h+1FCh ; BS offset 508 (bp+508) 497 bsReserved1: 498 000001FC 5452 db 'TR' ; 'Turkish Rational DOS' feature identifier. 499 bootsignature1: 500 000001FE 55AA db 55h, 0AAh