1 ; **************************************************************************** 2 ; TRDOS386.ASM (TRDOS 386 Kernel) - v2.0.0 - fat32_bs.s - FAT32 BOOT SECTOR 3 ; ---------------------------------------------------------------------------- 4 ; Last Update: 30/01/2018 5 ; ---------------------------------------------------------------------------- 6 ; Beginning: 13/12/2017 7 ; ---------------------------------------------------------------------------- 8 ; Assembler: NASM version 2.11 9 ; ---------------------------------------------------------------------------- 10 ; ((nasm fat32_bs.s -l fat32_bs.lst -o FAT32_BS.BIN)) 11 ; ---------------------------------------------------------------------------- 12 ; Turkish Rational DOS 13 ; Operating System Project v2.0 by ERDOGAN TAN (Beginning: 04/01/2016) 14 ; 15 ; This boot sector code occupies 2 sectors.. as below: 16 ; * Boot Sector 1: 17 ; The 1st 512 bytes of this boot code will be on sector 0 (of the partition). 18 ; * Boot Sector 2: 19 ; Remain bytes of this boot code will be sector 2 (just after FSINFO sector) 20 ; of the (FAT32) partition. 21 ; 22 ; NOTE: This code has some tricks and TRDOS 386 specific modifications 23 ; which are not a part of original Microsoft Windows (XP) FAT32 BS code. 24 ; (Purpose of TRDOS 386 specific modifications and tricks is 25 ; to load 'TRDOS386.SYS' kernel file as easy and as correct, 26 ; without affecting FAT32 FS recognization for other operating systems.) 27 ; 28 ; Note: Modifications (on WINDOWS 98 FAT32 boot sector code) 29 ; are based on WINDOWS XP FAT32 boot sector(s) code (2 sectors), 30 ; which is disassembled by Erdogan Tan (12/12/2017) 31 ; by using BINFILEHEX (Erdogan Tan) & IDA PRO FREE (Hex-Rays SA) 32 ; programs. 33 ; 34 ; Derived from Microsoft WINDOWS 98 FAT 32 boot sector code 35 ; which is edited/disassembled by Erdogan Tan (04/10/2003). 36 ; 37 ; Derived from 'trfdbs.s' TRDOS 386 FAT12 (3.5") floppy disk boot sector 38 ; source code by Erdogan Tan (06/07/2017). 39 ; **************************************************************************** 40 ; incbin "FAT32_BS.BIN" (in 'hdimage.s' & 'hdformat.s') 41 42 rts_segment equ 1000h 43 44 [BITS 16] 45 [ORG 7C00h] 46 BS_jmpBoot: 47 00000000 EB58 jmp short loc_5A ; jmp short start 48 BS_jmpBoot_nop: 49 00000002 90 nop 50 51 ; BootSector Identification (Data) Block 52 BS_OEMName: 53 00000003 4D5357494E342E31 db 'MSWIN4.1' ; bp+3 54 0000000B 0002 BPB_BytesPerSec: dw 512 ; bp+11 55 0000000D 08 BPB_SecPerClus: db 8 ; bp+13 56 0000000E 2000 BPB_RsvdSecCnt: dw 32 ; bp+14 57 00000010 02 BPB_NumFATs: db 2 ; bp+16 58 00000011 0000 BPB_RootEntCnt: dw 0 ; bp+17 59 00000013 0000 BPB_TotSec16: dw 0 ; bp+19 60 00000015 F8 BPB_Media: db 0F8h ; bp+21 61 00000016 0000 BPB_FATSz16: dw 0 ; bp+22 62 00000018 3F00 BPB_SecPerTrk: dw 63 ; bp+24 63 0000001A FF00 BPB_NumHeads: dw 255 ; bp+26 64 0000001C 01000000 BPB_HiddSec: dd 1 ; bp+28 65 00000020 00000000 BPB_TotSec32: dd 0 ; bp+32 66 00000024 00000000 BPB_FATSz32: dd 0 ; bp+36 67 00000028 0000 BPB_ExtFlags: dw 0 ; bp+40 68 0000002A 0000 BPB_FSVer: dw 0 ; bp+42 69 0000002C 02000000 BPB_RootClus: dd 2 ; bp+44 70 00000030 0100 BPB_FSInfo: dw 1 ; bp+48 71 00000032 0600 BPB_BkBootSec: dw 6 ; bp+50 72 00000034 00 BPB_Reserved: times 12 db 0 ; bp+52 73 00000040 80 BS_DrvNum: db 80h ; bp+64 74 00000041 00 BS_Reserved1: db 0 ; bp+65 75 00000042 29 BS_BootSig: db 29h ; bp+66 76 00000043 00000000 BS_VolID: dd 0 ; bp+67 77 00000047 5452444F5333383620- BS_VolLab: db 'TRDOS386 ' ; bp+71 77 00000050 2020 78 00000052 4641543332202020 BS_FilSysType: db 'FAT32 ' ; bp+82 79 80 start: 81 loc_5A: 82 0000005A 09C0 OR AX, AX ; db 09h, C0h (db 0Bh, C0h) 83 ; TRDOS 386 (FAT32 BS) LBA check trick!! 84 85 0000005C BD007C mov bp, 7C00h 86 87 ; ((WINDOWS XP FAT 32 boot sector code checks Masterboot 88 ; partition table for partition type, if it is 0Ch 89 ; -FAT32 LBA-, the boot code changes 90h at BS offset 2 90 ; to 0Eh. Then a 0Eh at this addr is used as identifier, 91 ; for reading disk sector by using INT 13h -LBA read- 92 ; extension.)) 93 94 0000005F 3DA101 cmp ax, 417 ; If AX=417, the masterboot sector 95 ; has a SINGLIX FS (& TRDOS 386) 96 ; masterboot code; and... 97 ; DX=ES=SS=0, BP=7C00h 98 ; SP=7C00h ... masterboot sector has 99 ; been loaded at 0:600h, it has 100 ; CHS parameters at offset 600h+420. 101 ; (There is a 01A1h in offset 600h+417) 102 103 00000062 740F je short bs_01 ; no need to following assignments ! 104 105 00000064 31C0 xor ax, ax 106 00000066 8ED8 mov ds, ax 107 00000068 8EC0 mov es, ax 108 0000006A FA cli 109 0000006B 8ED0 mov ss, ax 110 0000006D 89EC mov sp, bp 111 0000006F FB sti 112 00000070 8A5640 mov dl, [bp+40h] ; [BS_DrvNum] 113 bs_01: 114 00000073 8936[FC01] mov [bsReserved1], si ; Partition entry address.. 115 ; 24/12/2017 ; (from Singlix FS MBR) 116 ; (7BEh,7CEh,7DEh,7EEh) 117 118 ; Check Bytes/Sector value 119 ; It must be 512 !? (at least, for TRDOS386) 120 00000077 817E0B0002 cmp word [bp+0Bh], 512 ; [BPB_BytesPerSec] 121 0000007C 7578 jne invalid_system_disk 122 123 ; Following validation checks (*!*) 124 ; are done according to 125 ; Microsoft Extensible Firmware Initiative 126 ; FAT32 File System Specification, 127 ; Version 1.03 (2000). 128 129 ; [BPB_FATSz16] must be 0 (!*!) ; [bp+16h] 130 0000007E 6629C9 sub ecx, ecx ; 0 ; * 131 ;cmp [BPB_FATSz16], cx ; 0 ; sectors/fat for FAT16 132 00000081 394E16 cmp [bp+16h], cx 133 00000084 7570 jne short invalid_system_disk 134 135 ; [BPB_FSVer] must be 0 for current FAT32 version (!*!) 136 ;cmp [BPB_FSVer], cx ; 0 ; [bp+2Ah], FAT32 version 137 00000086 394E2A cmp [bp+2Ah], cx 138 00000089 756B jne short invalid_system_disk 139 140 ;mov dh, [bp+5Ah] ; 0Ch (FAT32 LBA) or 0Bh (FAT32 CHS) 141 ; NOTE: 09h at bp+5Ah (at loc_5A) will be overwritten 142 ; by TRDOS 386 disk format program. 143 ; (0BC0h -or AX,AX- is written for FAT32 CHS partition, 144 ; 0C00h -or AL,0- is written for FAT32 LBA partition.) 145 146 ; overwrite hd drive number ! 147 ;mov [BS_DrvNum], dl ; drive number from INT 19h 148 0000008B 885640 mov [bp+40h], dl 149 ;mov [bp+41h], dh ; [BS_Reserved1] = Partition ID !!! 150 ;mov [bp+40h], dx 151 152 ; reset FAT32 FS reading pointers and set SP to 7BF4h 153 ;xor ecx, ecx ; * 154 ;sub ecx, ecx ; * 155 0000008E 6651 push ecx ; [bp-4] = 0 ; CHS limit (8.4GB) 156 00000090 6651 push ecx ; [bp-8] = 0 ; Address of Cluster 2 157 00000092 6649 dec ecx ; 0FFFFFFFFh 158 00000094 6651 push ecx ; [bp-12] = -1 ; FAT sector in FAT buffer 159 00000096 6641 inc ecx ; 0 160 161 ; SP = 7BF4h 162 163 ; check for ROMBIOS INT 13h extensions 164 00000098 B441 mov ah, 41h 165 ;mov ebx, 55AAh 166 0000009A BBAA55 mov bx, 55AAh 167 ;mov dl, [BS_DrvNum] 168 ;mov dl, [bp+40h] 169 0000009D CD13 int 13h 170 0000009F 721A jc short bs_02 171 000000A1 81FB55AA cmp bx, 0AA55h 172 000000A5 7514 jne short bs_02 173 000000A7 F6C101 test cl, 1 174 000000AA 740F jz short bs_02 175 176 ; ROMBIOS INT 13h extentions are present... 177 178 000000AC B8424A mov ax, 4A42h 179 ;mov [BS_jmpBoot+2], al ; 42h ; 'LBA mode is available' 180 000000AF 884602 mov [bp+2], al ; 42h 181 ;cmp dh, 0Ch ; is this BS of a FAT32 LBA partition? 182 000000B2 807E5A0C cmp byte [bp+5Ah], 0Ch 183 000000B6 7503 jne short bs_02 ; no.. 184 ; yes, put sign for disk read subroutine (for LBA read) 185 ;mov [loc_5A], ax 186 000000B8 89465A mov [bp+5Ah], ax ; INC DX (FAT32 LBA read), DEC X 187 bs_02: 188 ; ..CHS limit setup.. 189 190 ; Get drive parameters (CHS parameters) 191 ;mov dl, [BS_DrvNum] 192 ;mov dl, [bp+40h] 193 000000BB B408 mov ah, 08h 194 000000BD CD13 int 13h 195 000000BF 7241 jc short disk_io_error 196 197 ; CX = maximum value for cylinder and sector 198 ; DH = maximum value for head 199 ; DL = number of harddisks on first controller 200 ; ES:DI = address of hard disk parameters table 201 ; (Bits 6&7 of CL is high 2 bits of 10 bit clinder value 202 ; which is low 8 bits are in CH.) 203 204 000000C1 1E push ds 205 000000C2 07 pop es 206 207 ; convert CHS values to CHS limit (as LBA) 208 000000C3 660FB6C6 movzx eax, dh 209 000000C7 40 inc ax 210 ;movzx edx, cl 211 000000C8 88CA mov dl, cl 212 ;and dl, 3Fh 213 000000CA 83E23F and dx, 3Fh 214 000000CD F7E2 mul dx 215 000000CF C0E906 shr cl, 6 216 000000D2 86CD xchg cl, ch 217 000000D4 41 inc cx 218 ;movzx ecx, cx ; * 219 000000D5 66F7E1 mul ecx 220 000000D8 668946FC mov [bp-4], eax ; dword [7BFCh] ; CHS limit 221 222 ; Load the second half (remain bytes) of this boot code 223 ; at 7E00h. 224 225 000000DC 668B461C mov eax, [bp+1Ch] ; [BPB_HiddSec] 226 000000E0 6683C002 add eax, 2 ; Second half of boot code is in BS 2 227 ;mov ebx, 7E00h 228 000000E4 BB007E mov bx, 7E00h 229 ;mov cx, 1 230 ;call disk_read 231 000000E7 E83500 call read_sector ; 25/12/2017 (Read 1 sector) 232 000000EA 7216 jc short disk_io_error 233 234 ; Boot sector 2 validation check 235 000000EC 813EA17FA101 cmp word [7FA1h], 417 ; The magic word ! 236 000000F2 0F840C01 je check_root_dir_entries 237 238 invalid_system_disk: 239 000000F6 BE[9F01] mov si, Inv_disk_Msg 240 000000F9 E81400 call print_msg 241 getchar_reboot: 242 ; Wait for a keystroke just before reboot 243 000000FC 30E4 xor ah, ah 244 000000FE CD16 int 16h 245 246 00000100 CD19 int 19h ; disk boot 247 ; causes reboot of disk system 248 disk_io_error: 249 00000102 BE[8E01] mov si, Diskio_err_Msg 250 00000105 E80800 call print_msg 251 ;replace_disk: 252 ; mov si, Replace_Msg 253 replace_disk: 254 00000108 BE[B401] mov si, Disk_err_replace_Msg 255 0000010B E80200 call print_msg 256 0000010E EBEC jmp getchar_reboot 257 258 print_msg: 259 ; DS:SI = Error message address (ASCIIZ string) 260 00000110 B40E mov ah, 0Eh 261 00000112 BB0700 mov bx, 7 262 bs_03: 263 00000115 AC lodsb 264 00000116 84C0 test al, al 265 00000118 7404 jz short bs_04 266 0000011A CD10 int 10h 267 0000011C EBF7 jmp short bs_03 268 bs_04: 269 0000011E C3 retn 270 271 read_sector: ; 25/12/2017 (Read 1 sector) 272 0000011F B90100 mov cx, 1 273 disk_read: 274 ;mov byte [bp+retry_count-7C00h], 4 275 00000122 B204 mov dl, 4 ; retry count 276 disk_read_0: 277 00000124 6660 pushad 278 ;cmp byte [loc_5A], 42h ; FAT32 LBA availability 279 00000126 B242 mov dl, 42h 280 00000128 38565A cmp [bp+5Ah], dl ; 42h ; FAT32 LBA partition & LBA ready 281 0000012B 740D je short lba_read 282 ; Jump to lba_read if sector addr overs CHS limit 283 0000012D 663B46FC cmp eax, [bp-4] ; CHS limit ([7BFCh]) 284 00000131 721E jb short chs_read 285 ; Disk I/O error if Int 13h LBA read func is not usable 286 ; byte [BS_jmpBoot+2] = 'LBA read function is ready' sign 287 ;cmp byte [[BS_jmpBoot+2], 42h ; FAT32 LBA availability 288 ;cmp byte [bp+2], 42h 289 00000133 385602 cmp [bp+2], dl ; 42h ; is LBA mode ready ? 290 00000136 7402 je short lba_read ; LBA mode is usable/available 291 00000138 F9 stc ; cf = 1 292 00000139 C3 retn 293 lba_read: 294 ;pushad 295 296 ;mov di, sp 297 298 0000013A 666A00 push dword 0 299 0000013D 6650 push eax 300 0000013F 06 push es 301 00000140 53 push bx 302 00000141 6A01 push byte 1 303 00000143 6A10 push byte 16 ; 10h 304 ;mov ah, 42h 305 00000145 88D4 mov ah, dl ; 42h 306 ;mov dl, [BS_DrvNum] 307 00000147 8A5640 mov dl, [bp+40h] 308 0000014A 89E6 mov si, sp 309 0000014C CD13 int 13h 310 311 ;pop eax 312 ;pop eax 313 ;pop eax 314 ;pop eax 315 ;mov sp, di 316 317 0000014E 61 popa 318 0000014F EB2A jmp short disk_read_1 319 chs_read: 320 ;pushad 321 322 ; Convert LBA to CHS 323 00000151 6631D2 xor edx, edx 324 ;movzx ecx, word [BPB_SecPerTrk] ; [bp+18h] 325 ; sectors per track (17 or 63) 326 00000154 660FB74E18 movzx ecx, word [bp+18h] 327 00000159 66F7F1 div ecx 328 0000015C FEC2 inc dl ; sector number (1 based) 329 0000015E 88D1 mov cl, dl 330 00000160 6689C2 mov edx, eax ; (heads * cylinder) + head number 331 00000163 66C1EA10 shr edx, 16 ; high word in DX, low word in AX 332 ;div word [BPB_NumHeads] ; [bp+1Ah] 333 ; number of heads (2 to 255) 334 00000167 F7761A div word [bp+1Ah] 335 ; AX = cylinder (0 to 1023) 336 ; DX = head number (in DL) 337 0000016A 88D6 mov dh, dl ; head number in DH 338 ;mov dl, [BS_DrvNum] ; [bp+40h] ; Drive number (80h) 339 0000016C 8A5640 mov dl, [bp+40h] 340 0000016F 88C5 mov ch, al ; Low 8 bits of cylinder number (0 to 7) 341 00000171 C0E406 shl ah, 6 ; High 2 bits of cylinder is in bit 7&8 342 00000174 08E1 or cl, ah ; High two bits of CL is cylinder bits 8&9 343 00000176 B80102 mov ax, 201h ; Read 1 sector 344 00000179 CD13 int 13h 345 disk_read_1: 346 0000017B 6661 popad 347 0000017D 7305 jnc short disk_read_2 348 ; cf = 1 349 ;dec byte [retry_count] 350 ;dec byte [bp+retry_count-7C00h] 351 0000017F FECA dec dl ; Retry count 352 00000181 75A1 jnz short disk_read_0 ; Retry 353 ; cf = 1 354 00000183 C3 retn 355 disk_read_2: 356 ;add bx, [bp+0Bh] ; [BPB_BytesPerSec] ; 512 357 ;add bx, 512 358 00000184 80C702 add bh, 2 ; ** 359 00000187 6640 inc eax 360 00000189 49 dec cx 361 0000018A 7596 jnz short disk_read 362 ;clc ; ** (128 sectors/cluster!?) 363 0000018C C3 retn 364 365 0000018D 07 db 07h 366 Diskio_err_Msg: 367 0000018E 0D0A db 0Dh, 0Ah 368 00000190 4469736B20492F4F20- db 'Disk I/O error' 368 00000199 6572726F72 369 ;db '!' 370 0000019E 00 db 0 371 Inv_disk_Msg: 372 0000019F 0D0A db 0Dh, 0Ah 373 000001A1 496E76616C69642073- db 'Invalid system disk' 373 000001AA 797374656D20646973- 373 000001B3 6B 374 Disk_err_replace_Msg: 375 000001B4 21 db '!' 376 Replace_Msg: 377 000001B5 0D0A db 0Dh, 0Ah 378 000001B7 5265706C6163652074- db 'Replace the disk and press any key to reboot.' 378 000001C0 6865206469736B2061- 378 000001C9 6E6420707265737320- 378 000001D2 616E79206B65792074- 378 000001DB 6F207265626F6F742E 379 000001E4 0D0A00 db 0Dh, 0Ah, 0 380 381 ; Boot sector code writing date (by Erdogan Tan) 382 000001E7 1E db 30 383 000001E8 01 db 01 384 000001E9 E207 dw 2018 385 386 ; TRDOS 386 FAT32 boot sector code version 387 000001EB 76312E30 db 'v1.0' 388 389 000001EF 00 times (508+rtsfilename-bsReserved1) - ($ - $$) db 0 390 rtsfilename: 391 000001F0 5452444F5333383653- db 'TRDOS386SYS' 391 000001F9 5953 392 000001FB 00 db 0 393 bsReserved1: 394 000001FC 5452 db 'TR' ; 'Turkish Rational DOS' feature identifier. 395 bootsignature1: 396 000001FE 55AA db 55h, 0AAh 397 398 bsReserved2: 399 00000200 5254 db 'RT' ; 'Turkish Rational DOS' feature identifier 400 401 check_root_dir_entries: 402 ; load root directory and check directory entries 403 404 ; calculate total size of FAT area 405 ;movzx ecx, byte [BPB_NumFATs] ; [bp+10h] ; number of FATs 406 00000202 8A4E10 mov cl, [bp+10h] 407 ;mov eax, [BPB_FATSz32] ; [bp+24h] ; sectors per FAT 408 00000205 668B4624 mov eax, [bp+24h] 409 00000209 66F7E1 mul ecx 410 411 ; add hidden sectors 412 ;add eax, [BPB_HiddSec] ; [bp+1Ch] 413 0000020C 6603461C add eax, [bp+1Ch] 414 415 ; add reserved sectors 416 ;movzx edx, [BPB_RsvdSecCnt] ; [bp+0Eh] 417 ;mov dx, [BPB_RsvdSecCnt] 418 00000210 8B560E mov dx, [bp+0Eh] 419 00000213 6601D0 add eax, edx 420 421 ; Save address of cluster 2 into 7BF8h 422 00000216 668946F8 mov [bp-8], eax ; EAX = Data Area (Cluster 2) 423 ; (Data) Start Address in 7BF8h 424 425 ; Reset FAT sector address pointer (7BF4h) 426 ; which points to FAT sectors in the FAT buffer 427 ; (8000h) 428 ; 429 ;mov dword [bp-12], 0FFFFFFFFh ; invalid address 430 ; (for now) 431 432 ; Check Root Directory Start Cluster is valid or not. 433 ;mov eax, [BPB_RootClus] ; [bp+2Ch] 434 0000021A 668B462C mov eax, [bp+2Ch] 435 436 load_root_dir_sector: 437 ; EAX = Cluster Number 438 439 ; Cluster number must not be less than 2 440 0000021E 6683F802 cmp eax, 2 ; Is it Cluster 2? 441 00000222 0F82D0FE jb invalid_system_disk ; error if less than 2 442 443 ; Is it End Of Cluster Chain marker or something above? 444 ;cmp eax, 0FFFFFF8h ; clust 2 to 0FFFFFF7h is valid 445 ;jnb invalid_system_disk ; invalid cluster num 446 ; or end of cluster chain 447 ; 23/12/2017 448 ; Note: Bad Cluster number is 0FFFFFF7h ! 449 ; (According to MS FAT32 Specification, 2000, page 18) 450 ; "It is not possible for the bad cluster mark to be 451 ; an allocatable cluster number on FAT12 and FAT16 volumes, 452 ; but it is feasible for 0x0FFFFFF7 to be an allocatable 453 ; cluster number on FAT32 volumes. 454 ; To avoid possible confusion by disk utilities, 455 ; no FAT32 volume should ever be configured such that 456 ; 0x0FFFFFF7 is an allocatable cluster number." 457 458 ; Is it End Of Cluster Chain marker or something above? 459 00000226 663DF7FFFF0F cmp eax, 0FFFFFF7h ; clust 2 to 0FFFFFF6h is valid 460 0000022C 0F83C6FE jnb invalid_system_disk ; invalid cluster num 461 ; or end of cluster chain 462 00000230 6650 push eax 463 00000232 6683E802 sub eax, 2 ; 0 based cluster number 464 ;movzx ebx, byte [BPB_SecPerClus] ; [bp+13] 465 00000236 660FB65E0D movzx ebx, byte [bp+0Dh] 466 0000023B 89DE mov si, bx ; save sector per cluster in SI 467 0000023D 66F7E3 mul ebx 468 ; EAX = relative sector of the 1st part of root dir 469 00000240 660346F8 add eax, [bp-8] ; add 'start address of data area' 470 ; (in 7BF8h) to relative address 471 bs_05: 472 00000244 BB0082 mov bx, 8200h ; Root directory buffer (1 sector) 473 00000247 89DF mov di, bx 474 ;mov cx, 1 475 ;call disk_read 476 00000249 E8D3FE call read_sector ; 25/12/2017 (Read 1 sector) 477 0000024C 0F82B2FE jc disk_io_error 478 479 ; BX = 8400h 480 481 search_startup_file: 482 ; check/compare root dir entry for/with kernel file 483 00000250 382D cmp [di], ch ; 0 484 00000252 0F84A0FE je invalid_system_disk ; kernel not found! 485 00000256 B10B mov cl, 11 ; 0Bh 486 ; SI = count down value from 'sectors per cluster' 487 00000258 56 push si ; SPC to 1 488 00000259 BE[F001] mov si, rtsfilename ; Run Time System file name 489 ; or Kernel file name 490 ; (or Startup file name) 491 ; (or Standalone file name) 492 ; in MSDOS directory entry 493 ; format. ('TRDOS386SYS') 494 ; It is 'TRDOS386.SYS' 495 ; for TRDOS 386 OS. 496 0000025C F3A6 repe cmpsb ; compare dir entry and kernel's name 497 0000025E 5E pop si 498 0000025F 7475 jz load_startup_file ; kernel is there! 499 00000261 01CF add di, cx 500 00000263 83C715 add di, 21 ; 15h (11+21=32) 501 00000266 39DF cmp di, bx ; 8400h 502 00000268 72E6 jb short search_startup_file ; chk next entry 503 ; Sector Per Cluster countdown 504 0000026A 4E dec si 505 0000026B 75D7 jnz short bs_05 ; next sector in same cluster 506 0000026D 6658 pop eax 507 0000026F E80600 call get_next_cluster 508 00000272 0F828CFE jc disk_io_error 509 ;; EAX = 32 bit cluster number (32 bit FAT entry) 510 ;and eax, 0FFFFFFFh ; 28 bit cluster number 511 00000276 EBA6 jmp short load_root_dir_sector 512 513 get_next_cluster: ; get next (FAT32) directory/file cluster 514 ; EAX = current cluster number (28 bit, zero based) 515 00000278 66C1E002 shl eax, 2 ; 32 bit FAT entry offset 516 0000027C E80D00 call get_fat32_entry 517 0000027F 720A jc short bs_06 ; Disk read error! 518 00000281 26668B01 mov eax, [es:bx+di] ; 32 bit clust entry number 519 00000285 6625FFFFFF0F and eax, 0FFFFFFFh ; 28 bit cluster number 520 ;cmp eax, 0FFFFFF8h 521 ;cmp eax, 0FFFFFF7h ; 23/12/2017 522 ;cmc 523 bs_06: 524 0000028B C3 retn 525 526 get_fat32_entry: 527 ; EAX = 32 bit FAT entry (dword) offset 528 0000028C BF0080 mov di, 8000h ; FAT (sector) buffer 529 ;movzx ecx, word [BPB_BytesPerSec] ; [bp+11] 530 ;mov cx, [BPB_BytesPerSec] 531 ;mov cx, [bp+0Bh] 532 0000028F B90002 mov cx, 512 533 ;xor edx, edx 534 00000292 31D2 xor dx, dx 535 00000294 66F7F1 div ecx 536 ; EAX = FAT sector number (relative) 537 ; Check FAT sector number if it is already 538 ; in FAT buffer at 8000h. 539 ; Current FAT sector is in 7BF4h. 540 ; (Note: initial FAT sector value in 7BF4h is 541 ; 0FFFFFFFFh which means the buff 542 ; is not loaded yet..) 543 00000297 663B46F4 cmp eax, [bp-0Ch] ; [7BF4h] 544 0000029B 7431 je short bs_08 ; same sector in FAT buffer 545 0000029D 668946F4 mov [bp-0Ch], eax ; save FAT sector number 546 ; Calculate absolute (LBA) address of FAT sector 547 ; by adding hidden (partition's start sector) 548 ; and reserved sectors (between BS and FAT). 549 ;add eax, [BPB_HiddSec] ; [bp+1Ch] 550 000002A1 6603461C add eax, [bp+1Ch] 551 ;movzx ecx, word [BPB_RsvdSecCnt] ; [bp+0Eh] 552 ;mov cx, [BPB_RsvdSecCnt] ; = 32 (typically) 553 000002A5 8B4E0E mov cx, [bp+0Eh] 554 000002A8 6601C8 add eax, ecx ; LBA of the FAT sector 555 ; Check FAT mirroring flag.. 556 ; bits 0 to 3 are used for active FAT number 557 ; If bit 7 is 1, only one (active) FAT copy 558 ; is updated (written without mirroring). 559 ; (Default active FAT is 0 and default option 560 ; is to mirror the active FAT -at runtime- into 561 ; all FAT copies -generally 2 FATs-. 562 ;movzx ebx, word [BPB_ExtFlags] ; [bp+28h] 563 ;mov bx, [BPB_ExtFlags] 564 000002AB 8B5E28 mov bx, [bp+28h] 565 000002AE 83E30F and bx, 0Fh 566 000002B1 7414 jz short bs_07 ; FAT number 0 is active 567 ; (as default) 568 ; compare active FAT number with number of FATs 569 ;cmp bl, [BPB_NumFATs] ; [bp+10h] 570 000002B3 3A5E10 cmp bl, [bp+10h] 571 000002B6 7319 jnb short bs_09 ; invalid parameter! 572 000002B8 52 push dx 573 000002B9 6689C1 mov ecx, eax 574 ; multiply zero based FAT number with FAT size 575 ;mov eax, [BPB_FATSz32] ; [bp+24h] 576 000002BC 668B4624 mov eax, [bp+24h] 577 000002C0 66F7E3 mul ebx 578 000002C3 6601C8 add eax, ecx ; start of active FAT copy 579 000002C6 5A pop dx 580 bs_07: 581 000002C7 52 push dx 582 000002C8 89FB mov bx, di 583 ;mov cx, 1 584 ;call disk_read 585 000002CA E852FE call read_sector ; 25/12/2017 (Read 1 sector) 586 ; If cf = 1 -> Disk I/O err, not invalid sys disk! 587 000002CD 5A pop dx 588 bs_08: 589 000002CE 89D3 mov bx, dx 590 000002D0 C3 retn 591 bs_09: 592 ; Invalid boot sector parameter/data 593 ;add sp, 4 594 000002D1 58 pop ax ; return to 'get_next_cluster' 595 000002D2 58 pop ax ; return to 'search_startup_file' 596 000002D3 E920FE jmp invalid_system_disk 597 598 load_startup_file: 599 ; DI = directory entry offset 9 (of 32 bytes) 600 000002D6 83C404 add sp, 4 ; pop eax 601 ; High word of First Cluster 602 000002D9 8B4509 mov ax, [di+9] ; [di+DIR_FstClusHI-11] 603 ; Low word of First Cluster 604 000002DC 8B550F mov dx, [di+0Fh] ; [di+DIR_FstClusLO-11] 605 000002DF 66C1E010 shl eax, 16 606 000002E3 89D0 mov ax, dx 607 ; Valid cluster number must not be less than 2 608 ; and it (a first cluster value in directory entry) 609 ; must not be greater than 0FFFFFF6h. 610 000002E5 6683F802 cmp eax, 2 611 000002E9 0F8209FE jb invalid_system_disk 612 ;cmp eax, 0FFFFFF8h 613 000002ED 663DF7FFFF0F cmp eax, 0FFFFFF7h ; 23/12/2017 614 000002F3 0F83FFFD jnb invalid_system_disk 615 616 000002F7 6689C1 mov ecx, eax ; save first cluster number 617 618 ; Load RTS (Kernel) file 619 000002FA BE[4F03] mov si, Loading_Msg 620 000002FD E810FE call print_msg 621 622 00000300 6689C8 mov eax, ecx ; restore first cluster number 623 624 ;mov bx, rts_segment ; 1000h 625 ;mov [next_segment], bx 626 bs_10: 627 00000303 6650 push eax ; 28 bit cluster num, starts from 2 628 00000305 6683E802 sub eax, 2 ; now, cluster num starts from 0 629 ;movzx ecx, byte [BPB_SecPerClus] ; [bp+0Dh] 630 00000309 660FB64E0D movzx ecx, byte [bp+0Dh] 631 0000030E 66F7E1 mul ecx 632 ; eax = sector offset (from start of data area) 633 00000311 660346F8 add eax, [bp-8] ; add data area (start) addr 634 00000315 8B1E[4703] mov bx, [next_segment] 635 00000319 06 push es 636 0000031A 8EC3 mov es, bx ; segment = 1000h + 637 0000031C 31DB xor bx, bx ; offset = 0 638 ; CX = num of sectors to read (= sectors/cluster) 639 0000031E E801FE call disk_read 640 00000321 07 pop es 641 00000322 6658 pop eax 642 00000324 C1EB04 shr bx, 4 ; from byte count to paragraph count 643 00000327 011E[4703] add [next_segment], bx 644 0000032B E84AFF call get_next_cluster 645 ;jc short diskio_error 646 0000032E 720E jc short trdos_loading_error 647 ;cmp eax, 0FFFFFF8h 648 00000330 663DF7FFFF0F cmp eax, 0FFFFFF7h ; 23/12/2017 649 00000336 7351 jnb short bs_11 ; Startup file has been loaded. 650 651 00000338 6683F802 cmp eax, 2 652 ;jb invalid_system_disk 653 ;jmp short bs_10 ; load next clust of the file 654 0000033C 73C5 jnb short bs_10 655 656 trdos_loading_error: 657 0000033E BE[7303] mov si, Load_err_Msg 658 00000341 E8CCFD call print_msg 659 00000344 E9C1FD jmp replace_disk 660 next_segment: 661 00000347 0010 dw rts_segment 662 663 00000349 54522D444F53 db 'TR-DOS' ; Filler 664 665 0000034F 0D0A Loading_Msg: db 0Dh, 0Ah 666 00000351 4C6F6164696E67204B- db 'Loading Kernel TRDOS386.SYS ...' 666 0000035A 65726E656C20545244- 666 00000363 4F533338362E535953- 666 0000036C 202E2E2E 667 00000370 0D0A00 db 0Dh, 0Ah, 0 668 Load_err_Msg: 669 00000373 0D0A db 0Dh, 0Ah 670 00000375 5452444F53204C6F61- db 'TRDOS Loading Error' 670 0000037E 64696E67204572726F- 670 00000387 72 671 ;db '!' 672 00000388 00 db 0 673 674 bs_11: 675 ; Set TRDOS 386 kernel specific parameters (& signs) 676 ; and 677 ; Launch TRDOS 386 Kernel (Startup/RTS file) 678 679 ;mov dl, [BS_DrvNum] 680 00000389 8B5640 mov dx, [bp+40h] ; DL = Drive number, DH = 0 681 0000038C FEC6 inc dh ; TRDOS 386 FAT32 BS major version = 1 682 683 0000038E A1[4703] mov ax, [next_segment] ; 16 paragraphs after the 684 ; start of the last segment 685 ; of the kernel file loading 686 ; space. 687 ; So, (top of) stack will have 688 ; 256 bytes or more distance 689 ; from the last byte 690 ; of the kernel file. 691 ; (This will be enough for 692 ; TRDOS 386 kernel before 693 ; entering protected mode.) 694 00000391 FA cli 695 00000392 8ED0 mov ss, ax 696 00000394 BCFEFF mov sp, 0FFFEh 697 00000397 FB sti 698 699 00000398 BB0010 mov bx, rts_segment ; 1000h 700 0000039B 8EDB mov ds, bx 701 0000039D 8EC3 mov es, bx 702 ;mov fs, bx 703 ;mov gs, bx 704 705 ;xor ebx, ebx 706 ;xor ecx, ecx 707 ;xor edx, edx 708 ;xor esi, esi 709 ;xor edi, edi 710 ;xor ebp, ebp 711 712 ; bp = 7C00h 713 714 ; NOTE: Offset 417 in boot sector 2 (the 2nd half of VBR) 715 ; is also FAT32 boot record validation check address and 716 ; boot sector 2 must have 417 here for boot sector 1 code 717 ; (the 1st half of volume boot record). 718 ; ((So, 'mov eax, 417' has double meaning here.)) 719 loc_39F: 720 0000039F 66B8A1010000 mov eax, 417 ; TRDOS boot sector sign for TRDOS386.SYS 721 722 000003A5 EA00000010 jmp rts_segment:0 723 724 000003AA 00 times 1020 - ($ - $$) db 0 725 bsReserved3: 726 000003FC 5452 db 'TR' ; 'Turkish Rational DOS' feature identifier 727 bootsignature2: 728 000003FE 55AA db 55h, 0AAh