1 ; **************************************************************************** 2 ; TRDOS386.ASM (TRDOS 386 Kernel) - v2.0.0 - fat32_bs.s - FAT32 BOOT SECTOR 3 ; ---------------------------------------------------------------------------- 4 ; Last Update: 31/01/2018 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 78 00000050 2020 79 00000052 4641543332202020 BS_FilSysType: db 'FAT32 ' ; bp+82 80 81 start: 82 loc_5A: 83 0000005A 09C0 OR AX, AX ; db 09h, C0h (db 0Bh, C0h) 84 ; TRDOS 386 (FAT32 BS) LBA check trick!! 85 86 0000005C BD007C mov bp, 7C00h 87 88 ; ((WINDOWS XP FAT 32 boot sector code checks Masterboot 89 ; partition table for partition type, if it is 0Ch 90 ; -FAT32 LBA-, the boot code changes 90h at BS offset 2 91 ; to 0Eh. Then a 0Eh at this addr is used as identifier, 92 ; for reading disk sector by using INT 13h -LBA read- 93 ; extension.)) 94 95 0000005F 3DA101 cmp ax, 417 ; If AX=417, the masterboot sector 96 ; has a SINGLIX FS (& TRDOS 386) 97 ; masterboot code; and... 98 ; DX=ES=SS=0, BP=7C00h 99 ; SP=7C00h ... masterboot sector has 100 ; been loaded at 0:600h, it has 101 ; CHS parameters at offset 600h+420. 102 ; (There is a 01A1h in offset 600h+417) 103 104 00000062 740F je short bs_01 ; no need to following assignments ! 105 106 00000064 31C0 xor ax, ax 107 00000066 8ED8 mov ds, ax 108 00000068 8EC0 mov es, ax 109 0000006A FA cli 110 0000006B 8ED0 mov ss, ax 111 0000006D 89EC mov sp, bp 112 0000006F FB sti 113 00000070 8A5640 mov dl, [bp+40h] ; [BS_DrvNum] 114 bs_01: 115 00000073 8936[FC01] mov [bsReserved1], si ; Partition entry address.. 116 ; 24/12/2017 ; (from Singlix FS MBR) 117 ; (7BEh,7CEh,7DEh,7EEh) 118 119 ; Check Bytes/Sector value 120 ; It must be 512 !? (at least, for TRDOS386) 121 00000077 817E0B0002 cmp word [bp+0Bh], 512 ; [BPB_BytesPerSec] 122 0000007C 7578 jne invalid_system_disk 123 124 ; Following validation checks (*!*) 125 ; are done according to 126 ; Microsoft Extensible Firmware Initiative 127 ; FAT32 File System Specification, 128 ; Version 1.03 (2000). 129 130 ; [BPB_FATSz16] must be 0 (!*!) ; [bp+16h] 131 0000007E 6629C9 sub ecx, ecx ; 0 ; * 132 ;cmp [BPB_FATSz16], cx ; 0 ; sectors/fat for FAT16 133 00000081 394E16 cmp [bp+16h], cx 134 00000084 7570 jne short invalid_system_disk 135 136 ; [BPB_FSVer] must be 0 for current FAT32 version (!*!) 137 ;cmp [BPB_FSVer], cx ; 0 ; [bp+2Ah], FAT32 version 138 00000086 394E2A cmp [bp+2Ah], cx 139 00000089 756B jne short invalid_system_disk 140 141 ;mov dh, [bp+5Ah] ; 0Ch (FAT32 LBA) or 0Bh (FAT32 CHS) 142 ; NOTE: 09h at bp+5Ah (at loc_5A) will be overwritten 143 ; by TRDOS 386 disk format program. 144 ; (0BC0h -or AX,AX- is written for FAT32 CHS partition, 145 ; 0C00h -or AL,0- is written for FAT32 LBA partition.) 146 147 ; overwrite hd drive number ! 148 ;mov [BS_DrvNum], dl ; drive number from INT 19h 149 0000008B 885640 mov [bp+40h], dl 150 ;mov [bp+41h], dh ; [BS_Reserved1] = Partition ID !!! 151 ;mov [bp+40h], dx 152 153 ; reset FAT32 FS reading pointers and set SP to 7BF4h 154 ;xor ecx, ecx ; * 155 ;sub ecx, ecx ; * 156 0000008E 6651 push ecx ; [bp-4] = 0 ; CHS limit (8.4GB) 157 00000090 6651 push ecx ; [bp-8] = 0 ; Address of Cluster 2 158 00000092 6649 dec ecx ; 0FFFFFFFFh 159 00000094 6651 push ecx ; [bp-12] = -1 ; FAT sector in FAT buffer 160 00000096 6641 inc ecx ; 0 161 162 ; SP = 7BF4h 163 164 ; check for ROMBIOS INT 13h extensions 165 00000098 B441 mov ah, 41h 166 ;mov ebx, 55AAh 167 0000009A BBAA55 mov bx, 55AAh 168 ;mov dl, [BS_DrvNum] 169 ;mov dl, [bp+40h] 170 0000009D CD13 int 13h 171 0000009F 721A jc short bs_02 172 000000A1 81FB55AA cmp bx, 0AA55h 173 000000A5 7514 jne short bs_02 174 000000A7 F6C101 test cl, 1 175 000000AA 740F jz short bs_02 176 177 ; ROMBIOS INT 13h extentions are present... 178 179 000000AC B8424A mov ax, 4A42h 180 ;mov [BS_jmpBoot+2], al ; 42h ; 'LBA mode is available' 181 000000AF 884602 mov [bp+2], al ; 42h 182 ;cmp dh, 0Ch ; is this BS of a FAT32 LBA partition? 183 000000B2 807E5A0C cmp byte [bp+5Ah], 0Ch 184 000000B6 7503 jne short bs_02 ; no.. 185 ; yes, put sign for disk read subroutine (for LBA read) 186 ;mov [loc_5A], ax 187 000000B8 89465A mov [bp+5Ah], ax ; INC DX (FAT32 LBA read), DEC X 188 bs_02: 189 ; ..CHS limit setup.. 190 191 ; Get drive parameters (CHS parameters) 192 ;mov dl, [BS_DrvNum] 193 ;mov dl, [bp+40h] 194 000000BB B408 mov ah, 08h 195 000000BD CD13 int 13h 196 000000BF 7241 jc short disk_io_error 197 198 ; CX = maximum value for cylinder and sector 199 ; DH = maximum value for head 200 ; DL = number of harddisks on first controller 201 ; ES:DI = address of hard disk parameters table 202 ; (Bits 6&7 of CL is high 2 bits of 10 bit clinder value 203 ; which is low 8 bits are in CH.) 204 205 000000C1 1E push ds 206 000000C2 07 pop es 207 208 ; convert CHS values to CHS limit (as LBA) 209 000000C3 660FB6C6 movzx eax, dh 210 000000C7 40 inc ax 211 ;movzx edx, cl 212 000000C8 88CA mov dl, cl 213 ;and dl, 3Fh 214 000000CA 83E23F and dx, 3Fh 215 000000CD F7E2 mul dx 216 000000CF C0E906 shr cl, 6 217 000000D2 86CD xchg cl, ch 218 000000D4 41 inc cx 219 ;movzx ecx, cx ; * 220 000000D5 66F7E1 mul ecx 221 000000D8 668946FC mov [bp-4], eax ; dword [7BFCh] ; CHS limit 222 223 ; Load the second half (remain bytes) of this boot code 224 ; at 7E00h. 225 226 000000DC 668B461C mov eax, [bp+1Ch] ; [BPB_HiddSec] 227 000000E0 6683C002 add eax, 2 ; Second half of boot code is in BS 2 228 ;mov ebx, 7E00h 229 000000E4 BB007E mov bx, 7E00h 230 ;mov cx, 1 231 ;call disk_read 232 000000E7 E83500 call read_sector ; 25/12/2017 (Read 1 sector) 233 000000EA 7216 jc short disk_io_error 234 235 ; Boot sector 2 validation check 236 000000EC 813EA17FA101 cmp word [7FA1h], 417 ; The magic word ! 237 000000F2 0F840C01 je check_root_dir_entries 238 239 invalid_system_disk: 240 000000F6 BE[A001] mov si, Inv_disk_Msg 241 000000F9 E81400 call print_msg 242 getchar_reboot: 243 ; Wait for a keystroke just before reboot 244 000000FC 30E4 xor ah, ah 245 000000FE CD16 int 16h 246 247 00000100 CD19 int 19h ; disk boot 248 ; causes reboot of disk system 249 disk_io_error: 250 00000102 BE[8F01] mov si, Diskio_err_Msg 251 00000105 E80800 call print_msg 252 ;replace_disk: 253 ; mov si, Replace_Msg 254 replace_disk: 255 00000108 BE[B501] mov si, Disk_err_replace_Msg 256 0000010B E80200 call print_msg 257 0000010E EBEC jmp getchar_reboot 258 259 print_msg: 260 ; DS:SI = Error message address (ASCIIZ string) 261 00000110 B40E mov ah, 0Eh 262 00000112 BB0700 mov bx, 7 263 bs_03: 264 00000115 AC lodsb 265 00000116 84C0 test al, al 266 00000118 7404 jz short bs_04 267 0000011A CD10 int 10h 268 0000011C EBF7 jmp short bs_03 269 bs_04: 270 0000011E C3 retn 271 272 read_sector: ; 25/12/2017 (Read 1 sector) 273 0000011F B90100 mov cx, 1 274 disk_read: 275 ;mov byte [bp+retry_count-7C00h], 4 276 00000122 B204 mov dl, 4 ; retry count 277 disk_read_0: 278 00000124 6660 pushad 279 ;cmp byte [loc_5A], 42h ; FAT32 LBA availability 280 00000126 B242 mov dl, 42h 281 00000128 38565A cmp [bp+5Ah], dl ; 42h ; FAT32 LBA partition & LBA ready 282 0000012B 740D je short lba_read 283 ; Jump to lba_read if sector addr overs CHS limit 284 0000012D 663B46FC cmp eax, [bp-4] ; CHS limit ([7BFCh]) 285 00000131 721E jb short chs_read 286 ; Disk I/O error if Int 13h LBA read func is not usable 287 ; byte [BS_jmpBoot+2] = 'LBA read function is ready' sign 288 ;cmp byte [[BS_jmpBoot+2], 42h ; FAT32 LBA availability 289 ;cmp byte [bp+2], 42h 290 00000133 385602 cmp [bp+2], dl ; 42h ; is LBA mode ready ? 291 00000136 7402 je short lba_read ; LBA mode is usable/available 292 00000138 F9 stc ; cf = 1 293 00000139 C3 retn 294 lba_read: 295 ;pushad 296 297 ;mov di, sp 298 299 0000013A 666A00 push dword 0 300 0000013D 6650 push eax 301 0000013F 06 push es 302 00000140 53 push bx 303 00000141 6A01 push byte 1 304 00000143 6A10 push byte 16 ; 10h 305 ;mov ah, 42h 306 00000145 88D4 mov ah, dl ; 42h 307 ;mov dl, [BS_DrvNum] 308 00000147 8A5640 mov dl, [bp+40h] 309 0000014A 89E6 mov si, sp 310 0000014C CD13 int 13h 311 312 ;pop eax 313 ;pop eax 314 ;pop eax 315 ;pop eax 316 ;mov sp, di 317 318 0000014E 61 popa 319 0000014F EB2A jmp short disk_read_1 320 chs_read: 321 ;pushad 322 323 ; Convert LBA to CHS 324 00000151 6631D2 xor edx, edx 325 ;movzx ecx, word [BPB_SecPerTrk] ; [bp+18h] 326 ; sectors per track (17 or 63) 327 00000154 660FB74E18 movzx ecx, word [bp+18h] 328 00000159 66F7F1 div ecx 329 0000015C FEC2 inc dl ; sector number (1 based) 330 0000015E 88D1 mov cl, dl 331 00000160 6689C2 mov edx, eax ; (heads * cylinder) + head number 332 00000163 66C1EA10 shr edx, 16 ; high word in DX, low word in AX 333 ;div word [BPB_NumHeads] ; [bp+1Ah] 334 ; number of heads (2 to 255) 335 00000167 F7761A div word [bp+1Ah] 336 ; AX = cylinder (0 to 1023) 337 ; DX = head number (in DL) 338 0000016A 88D6 mov dh, dl ; head number in DH 339 ;mov dl, [BS_DrvNum] ; [bp+40h] ; Drive number (80h) 340 0000016C 8A5640 mov dl, [bp+40h] 341 0000016F 88C5 mov ch, al ; Low 8 bits of cylinder number (0 to 7) 342 00000171 C0E406 shl ah, 6 ; High 2 bits of cylinder is in bit 7&8 343 00000174 08E1 or cl, ah ; High two bits of CL is cylinder bits 8&9 344 00000176 B80102 mov ax, 201h ; Read 1 sector 345 00000179 CD13 int 13h 346 disk_read_1: 347 0000017B 6661 popad 348 0000017D 7305 jnc short disk_read_2 349 ; cf = 1 350 ;dec byte [retry_count] 351 ;dec byte [bp+retry_count-7C00h] 352 0000017F FECA dec dl ; Retry count 353 00000181 75A1 jnz short disk_read_0 ; Retry 354 ; cf = 1 355 00000183 C3 retn 356 disk_read_2: 357 ;add bx, [bp+0Bh] ; [BPB_BytesPerSec] ; 512 358 ;add bx, 512 359 00000184 80C702 add bh, 2 ; ** 360 00000187 6640 inc eax 361 00000189 49 dec cx 362 0000018A 7596 jnz short disk_read 363 ;clc ; ** (128 sectors/cluster!?) 364 0000018C C3 retn 365 366 ; Filler 367 0000018D 07 db 07h 368 0000018E 14 db 14h 369 370 Diskio_err_Msg: 371 0000018F 0D0A db 0Dh, 0Ah 372 00000191 4469736B20492F4F20- db 'Disk I/O error' 373 0000019A 6572726F72 374 ;db '!' 375 0000019F 00 db 0 376 Inv_disk_Msg: 377 000001A0 0D0A db 0Dh, 0Ah 378 000001A2 496E76616C69642073- db 'Invalid system disk' 379 000001AB 797374656D20646973- 380 000001B4 6B 381 Disk_err_replace_Msg: 382 000001B5 21 db '!' 383 Replace_Msg: 384 000001B6 0D0A db 0Dh, 0Ah 385 000001B8 5265706C6163652074- db 'Replace the disk and press any key to reboot.' 386 000001C1 6865206469736B2061- 387 000001CA 6E6420707265737320- 388 000001D3 616E79206B65792074- 389 000001DC 6F207265626F6F742E 390 000001E5 0D0A00 db 0Dh, 0Ah, 0 391 392 ; Boot sector code writing date (by Erdogan Tan) 393 000001E8 1F db 31 394 000001E9 01 db 01 395 000001EA E207 dw 2018 396 397 ; TRDOS 386 FAT32 boot sector code version 398 000001EC 76312E30 db 'v1.0' 399 400 times (508+rtsfilename-bsReserved1) - ($ - $$) db 0 401 rtsfilename: 402 000001F0 5452444F5333383653- db 'TRDOS386SYS' 403 000001F9 5953 404 000001FB 00 db 0 405 bsReserved1: 406 000001FC 5452 db 'TR' ; 'Turkish Rational DOS' feature identifier. 407 bootsignature1: 408 000001FE 55AA db 55h, 0AAh 409 410 bsReserved2: 411 00000200 5254 db 'RT' ; 'Turkish Rational DOS' feature identifier 412 413 check_root_dir_entries: 414 ; load root directory and check directory entries 415 416 ; calculate total size of FAT area 417 ;movzx ecx, byte [BPB_NumFATs] ; [bp+10h] ; number of FATs 418 00000202 8A4E10 mov cl, [bp+10h] 419 ;mov eax, [BPB_FATSz32] ; [bp+24h] ; sectors per FAT 420 00000205 668B4624 mov eax, [bp+24h] 421 00000209 66F7E1 mul ecx 422 423 ; add hidden sectors 424 ;add eax, [BPB_HiddSec] ; [bp+1Ch] 425 0000020C 6603461C add eax, [bp+1Ch] 426 427 ; add reserved sectors 428 ;movzx edx, [BPB_RsvdSecCnt] ; [bp+0Eh] 429 ;mov dx, [BPB_RsvdSecCnt] 430 00000210 8B560E mov dx, [bp+0Eh] 431 00000213 6601D0 add eax, edx 432 433 ; Save address of cluster 2 into 7BF8h 434 00000216 668946F8 mov [bp-8], eax ; EAX = Data Area (Cluster 2) 435 ; (Data) Start Address in 7BF8h 436 437 ; Reset FAT sector address pointer (7BF4h) 438 ; which points to FAT sectors in the FAT buffer 439 ; (8000h) 440 ; 441 ;mov dword [bp-12], 0FFFFFFFFh ; invalid address 442 ; (for now) 443 444 ; Check Root Directory Start Cluster is valid or not. 445 ;mov eax, [BPB_RootClus] ; [bp+2Ch] 446 0000021A 668B462C mov eax, [bp+2Ch] 447 448 load_root_dir_sector: 449 ; EAX = Cluster Number 450 451 ; Cluster number must not be less than 2 452 0000021E 6683F802 cmp eax, 2 ; Is it Cluster 2? 453 00000222 0F82D0FE jb invalid_system_disk ; error if less than 2 454 455 ; Is it End Of Cluster Chain marker or something above? 456 ;cmp eax, 0FFFFFF8h ; clust 2 to 0FFFFFF7h is valid 457 ;jnb invalid_system_disk ; invalid cluster num 458 ; or end of cluster chain 459 ; 23/12/2017 460 ; Note: Bad Cluster number is 0FFFFFF7h ! 461 ; (According to MS FAT32 Specification, 2000, page 18) 462 ; "It is not possible for the bad cluster mark to be 463 ; an allocatable cluster number on FAT12 and FAT16 volumes, 464 ; but it is feasible for 0x0FFFFFF7 to be an allocatable 465 ; cluster number on FAT32 volumes. 466 ; To avoid possible confusion by disk utilities, 467 ; no FAT32 volume should ever be configured such that 468 ; 0x0FFFFFF7 is an allocatable cluster number." 469 470 ; Is it End Of Cluster Chain marker or something above? 471 00000226 663DF7FFFF0F cmp eax, 0FFFFFF7h ; clust 2 to 0FFFFFF6h is valid 472 0000022C 0F83C6FE jnb invalid_system_disk ; invalid cluster num 473 ; or end of cluster chain 474 00000230 6650 push eax 475 00000232 6683E802 sub eax, 2 ; 0 based cluster number 476 ;movzx ebx, byte [BPB_SecPerClus] ; [bp+13] 477 00000236 660FB65E0D movzx ebx, byte [bp+0Dh] 478 0000023B 89DE mov si, bx ; save sector per cluster in SI 479 0000023D 66F7E3 mul ebx 480 ; EAX = relative sector of the 1st part of root dir 481 00000240 660346F8 add eax, [bp-8] ; add 'start address of data area' 482 ; (in 7BF8h) to relative address 483 bs_05: 484 00000244 BB0082 mov bx, 8200h ; Root directory buffer (1 sector) 485 00000247 89DF mov di, bx 486 ;mov cx, 1 487 ;call disk_read 488 00000249 E8D3FE call read_sector ; 25/12/2017 (Read 1 sector) 489 0000024C 0F82B2FE jc disk_io_error 490 491 ; BX = 8400h 492 493 search_startup_file: 494 ; check/compare root dir entry for/with kernel file 495 00000250 382D cmp [di], ch ; 0 496 00000252 0F84A0FE je invalid_system_disk ; kernel not found! 497 00000256 B10B mov cl, 11 ; 0Bh 498 ; SI = count down value from 'sectors per cluster' 499 00000258 56 push si ; SPC to 1 500 00000259 BE[F001] mov si, rtsfilename ; Run Time System file name 501 ; or Kernel file name 502 ; (or Startup file name) 503 ; (or Standalone file name) 504 ; in MSDOS directory entry 505 ; format. ('TRDOS386SYS') 506 ; It is 'TRDOS386.SYS' 507 ; for TRDOS 386 OS. 508 0000025C F3A6 repe cmpsb ; compare dir entry and kernel's name 509 0000025E 5E pop si 510 0000025F 7475 jz load_startup_file ; kernel is there! 511 00000261 01CF add di, cx 512 00000263 83C715 add di, 21 ; 15h (11+21=32) 513 00000266 39DF cmp di, bx ; 8400h 514 00000268 72E6 jb short search_startup_file ; chk next entry 515 ; Sector Per Cluster countdown 516 0000026A 4E dec si 517 0000026B 75D7 jnz short bs_05 ; next sector in same cluster 518 0000026D 6658 pop eax 519 0000026F E80600 call get_next_cluster 520 00000272 0F828CFE jc disk_io_error 521 ;; EAX = 32 bit cluster number (32 bit FAT entry) 522 ;and eax, 0FFFFFFFh ; 28 bit cluster number 523 00000276 EBA6 jmp short load_root_dir_sector 524 525 get_next_cluster: ; get next (FAT32) directory/file cluster 526 ; EAX = current cluster number (28 bit, zero based) 527 00000278 66C1E002 shl eax, 2 ; 32 bit FAT entry offset 528 0000027C E80D00 call get_fat32_entry 529 0000027F 720A jc short bs_06 ; Disk read error! 530 00000281 26668B01 mov eax, [es:bx+di] ; 32 bit clust entry number 531 00000285 6625FFFFFF0F and eax, 0FFFFFFFh ; 28 bit cluster number 532 ;cmp eax, 0FFFFFF8h 533 ;cmp eax, 0FFFFFF7h ; 23/12/2017 534 ;cmc 535 bs_06: 536 0000028B C3 retn 537 538 get_fat32_entry: 539 ; EAX = 32 bit FAT entry (dword) offset 540 0000028C BF0080 mov di, 8000h ; FAT (sector) buffer 541 ;movzx ecx, word [BPB_BytesPerSec] ; [bp+11] 542 ;mov cx, [BPB_BytesPerSec] 543 ;mov cx, [bp+0Bh] 544 0000028F B90002 mov cx, 512 545 ;xor edx, edx 546 00000292 31D2 xor dx, dx 547 00000294 66F7F1 div ecx 548 ; EAX = FAT sector number (relative) 549 ; Check FAT sector number if it is already 550 ; in FAT buffer at 8000h. 551 ; Current FAT sector is in 7BF4h. 552 ; (Note: initial FAT sector value in 7BF4h is 553 ; 0FFFFFFFFh which means the buff 554 ; is not loaded yet..) 555 00000297 663B46F4 cmp eax, [bp-0Ch] ; [7BF4h] 556 0000029B 7431 je short bs_08 ; same sector in FAT buffer 557 0000029D 668946F4 mov [bp-0Ch], eax ; save FAT sector number 558 ; Calculate absolute (LBA) address of FAT sector 559 ; by adding hidden (partition's start sector) 560 ; and reserved sectors (between BS and FAT). 561 ;add eax, [BPB_HiddSec] ; [bp+1Ch] 562 000002A1 6603461C add eax, [bp+1Ch] 563 ;movzx ecx, word [BPB_RsvdSecCnt] ; [bp+0Eh] 564 ;mov cx, [BPB_RsvdSecCnt] ; = 32 (typically) 565 000002A5 8B4E0E mov cx, [bp+0Eh] 566 000002A8 6601C8 add eax, ecx ; LBA of the FAT sector 567 ; Check FAT mirroring flag.. 568 ; bits 0 to 3 are used for active FAT number 569 ; If bit 7 is 1, only one (active) FAT copy 570 ; is updated (written without mirroring). 571 ; (Default active FAT is 0 and default option 572 ; is to mirror the active FAT -at runtime- into 573 ; all FAT copies -generally 2 FATs-. 574 ;movzx ebx, word [BPB_ExtFlags] ; [bp+28h] 575 ;mov bx, [BPB_ExtFlags] 576 000002AB 8B5E28 mov bx, [bp+28h] 577 000002AE 83E30F and bx, 0Fh 578 000002B1 7414 jz short bs_07 ; FAT number 0 is active 579 ; (as default) 580 ; compare active FAT number with number of FATs 581 ;cmp bl, [BPB_NumFATs] ; [bp+10h] 582 000002B3 3A5E10 cmp bl, [bp+10h] 583 000002B6 7319 jnb short bs_09 ; invalid parameter! 584 000002B8 52 push dx 585 000002B9 6689C1 mov ecx, eax 586 ; multiply zero based FAT number with FAT size 587 ;mov eax, [BPB_FATSz32] ; [bp+24h] 588 000002BC 668B4624 mov eax, [bp+24h] 589 000002C0 66F7E3 mul ebx 590 000002C3 6601C8 add eax, ecx ; start of active FAT copy 591 000002C6 5A pop dx 592 bs_07: 593 000002C7 52 push dx 594 000002C8 89FB mov bx, di 595 ;mov cx, 1 596 ;call disk_read 597 000002CA E852FE call read_sector ; 25/12/2017 (Read 1 sector) 598 ; If cf = 1 -> Disk I/O err, not invalid sys disk! 599 000002CD 5A pop dx 600 bs_08: 601 000002CE 89D3 mov bx, dx 602 000002D0 C3 retn 603 bs_09: 604 ; Invalid boot sector parameter/data 605 ;add sp, 4 606 000002D1 58 pop ax ; return to 'get_next_cluster' 607 000002D2 58 pop ax ; return to 'search_startup_file' 608 000002D3 E920FE jmp invalid_system_disk 609 610 load_startup_file: 611 ; DI = directory entry offset 9 (of 32 bytes) 612 000002D6 83C404 add sp, 4 ; pop eax 613 ; High word of First Cluster 614 000002D9 8B4509 mov ax, [di+9] ; [di+DIR_FstClusHI-11] 615 ; Low word of First Cluster 616 000002DC 8B550F mov dx, [di+0Fh] ; [di+DIR_FstClusLO-11] 617 000002DF 66C1E010 shl eax, 16 618 000002E3 89D0 mov ax, dx 619 ; Valid cluster number must not be less than 2 620 ; and it (a first cluster value in directory entry) 621 ; must not be greater than 0FFFFFF6h. 622 000002E5 6683F802 cmp eax, 2 623 000002E9 0F8209FE jb invalid_system_disk 624 ;cmp eax, 0FFFFFF8h 625 000002ED 663DF7FFFF0F cmp eax, 0FFFFFF7h ; 23/12/2017 626 000002F3 0F83FFFD jnb invalid_system_disk 627 628 000002F7 6689C1 mov ecx, eax ; save first cluster number 629 630 ; Load RTS (Kernel) file 631 000002FA BE[4F03] mov si, Loading_Msg 632 000002FD E810FE call print_msg 633 634 00000300 6689C8 mov eax, ecx ; restore first cluster number 635 636 ;mov bx, rts_segment ; 1000h 637 ;mov [next_segment], bx 638 bs_10: 639 00000303 6650 push eax ; 28 bit cluster num, starts from 2 640 00000305 6683E802 sub eax, 2 ; now, cluster num starts from 0 641 ;movzx ecx, byte [BPB_SecPerClus] ; [bp+0Dh] 642 00000309 660FB64E0D movzx ecx, byte [bp+0Dh] 643 0000030E 66F7E1 mul ecx 644 ; eax = sector offset (from start of data area) 645 00000311 660346F8 add eax, [bp-8] ; add data area (start) addr 646 00000315 8B1E[4703] mov bx, [next_segment] 647 00000319 06 push es 648 0000031A 8EC3 mov es, bx ; segment = 1000h + 649 0000031C 31DB xor bx, bx ; offset = 0 650 ; CX = num of sectors to read (= sectors/cluster) 651 0000031E E801FE call disk_read 652 00000321 07 pop es 653 00000322 6658 pop eax 654 00000324 C1EB04 shr bx, 4 ; from byte count to paragraph count 655 00000327 011E[4703] add [next_segment], bx 656 0000032B E84AFF call get_next_cluster 657 ;jc short diskio_error 658 0000032E 720E jc short trdos_loading_error 659 ;cmp eax, 0FFFFFF8h 660 00000330 663DF7FFFF0F cmp eax, 0FFFFFF7h ; 23/12/2017 661 00000336 7351 jnb short bs_11 ; Startup file has been loaded. 662 663 00000338 6683F802 cmp eax, 2 664 ;jb invalid_system_disk 665 ;jmp short bs_10 ; load next clust of the file 666 0000033C 73C5 jnb short bs_10 667 668 trdos_loading_error: 669 0000033E BE[7303] mov si, Load_err_Msg 670 00000341 E8CCFD call print_msg 671 00000344 E9C1FD jmp replace_disk 672 next_segment: 673 00000347 0010 dw rts_segment 674 675 00000349 54522D444F53 db 'TR-DOS' ; Filler 676 677 0000034F 0D0A Loading_Msg: db 0Dh, 0Ah 678 00000351 4C6F6164696E67204B- db 'Loading Kernel TRDOS386.SYS ...' 679 0000035A 65726E656C20545244- 680 00000363 4F533338362E535953- 681 0000036C 202E2E2E 682 00000370 0D0A00 db 0Dh, 0Ah, 0 683 Load_err_Msg: 684 00000373 0D0A db 0Dh, 0Ah 685 00000375 5452444F53204C6F61- db 'TRDOS Loading Error' 686 0000037E 64696E67204572726F- 687 00000387 72 688 ;db '!' 689 00000388 00 db 0 690 691 bs_11: 692 ; Set TRDOS 386 kernel specific parameters (& signs) 693 ; and 694 ; Launch TRDOS 386 Kernel (Startup/RTS file) 695 696 ;mov dl, [BS_DrvNum] 697 00000389 8B5640 mov dx, [bp+40h] ; DL = Drive number, DH = 0 698 0000038C FEC6 inc dh ; TRDOS 386 FAT32 BS major version = 1 699 700 0000038E A1[4703] mov ax, [next_segment] ; 16 paragraphs after the 701 ; start of the last segment 702 ; of the kernel file loading 703 ; space. 704 ; So, (top of) stack will have 705 ; 256 bytes or more distance 706 ; from the last byte 707 ; of the kernel file. 708 ; (This will be enough for 709 ; TRDOS 386 kernel before 710 ; entering protected mode.) 711 00000391 FA cli 712 00000392 8ED0 mov ss, ax 713 00000394 BCFEFF mov sp, 0FFFEh 714 00000397 FB sti 715 716 00000398 BB0010 mov bx, rts_segment ; 1000h 717 0000039B 8EDB mov ds, bx 718 0000039D 8EC3 mov es, bx 719 ;mov fs, bx 720 ;mov gs, bx 721 722 ;xor ebx, ebx 723 ;xor ecx, ecx 724 ;xor edx, edx 725 ;xor esi, esi 726 ;xor edi, edi 727 ;xor ebp, ebp 728 729 ; bp = 7C00h 730 731 ; NOTE: Offset 417 in boot sector 2 (the 2nd half of VBR) 732 ; is also FAT32 boot record validation check address and 733 ; boot sector 2 must have 417 here for boot sector 1 code 734 ; (the 1st half of volume boot record). 735 ; ((So, 'mov eax, 417' has double meaning here.)) 736 loc_39F: 737 0000039F 66B8A1010000 mov eax, 417 ; TRDOS boot sector sign for TRDOS386.SYS 738 739 000003A5 EA00000010 jmp rts_segment:0 740 741 000003AA 00 times 1020 - ($ - $$) db 0 742 bsReserved3: 743 000003FC 5452 db 'TR' ; 'Turkish Rational DOS' feature identifier 744 bootsignature2: 745 000003FE 55AA db 55h, 0AAh