wok annotate BootProg/stuff/boot32.asm @ rev 24535

Add some current_version
author Pascal Bellard <pascal.bellard@slitaz.org>
date Wed Feb 23 11:49:52 2022 +0000 (2022-02-23)
parents d77ab883a8b3
children d1f31f5f6401
rev   line source
pascal@24476 1 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 2 ;; ;;
pascal@24476 3 ;; "BootProg" Loader v 1.5 by Alexey Frunze (c) 2000-2015 ;;
pascal@24476 4 ;; 2-clause BSD license. ;;
pascal@24476 5 ;; ;;
pascal@24476 6 ;; ;;
pascal@24476 7 ;; How to Compile: ;;
pascal@24476 8 ;; ~~~~~~~~~~~~~~~ ;;
pascal@24476 9 ;; nasm boot32.asm -f bin -o boot32.bin ;;
pascal@24476 10 ;; ;;
pascal@24476 11 ;; ;;
pascal@24476 12 ;; Features: ;;
pascal@24476 13 ;; ~~~~~~~~~ ;;
pascal@24535 14 ;; - FAT32 supported using BIOS int 13h function 42h (IOW, it will only ;;
pascal@24535 15 ;; work with modern BIOSes supporting HDDs bigger than 8 GB) ;;
pascal@24476 16 ;; ;;
pascal@24476 17 ;; - Loads a 16-bit executable file in the MS-DOS .COM or .EXE format ;;
pascal@24476 18 ;; from the root directory of a disk and transfers control to it ;;
pascal@24476 19 ;; (the "ProgramName" variable holds the name of the file to be loaded) ;;
pascal@24525 20 ;; Its maximum size can be up to 636KB without Extended BIOS Data area. ;;
pascal@24476 21 ;; ;;
pascal@24476 22 ;; - Prints an error if the file isn't found or couldn't be read ;;
pascal@24476 23 ;; ("File not found" or "Read error") ;;
pascal@24476 24 ;; and waits for a key to be pressed, then executes the Int 19h ;;
pascal@24476 25 ;; instruction and lets the BIOS continue bootstrap. ;;
pascal@24476 26 ;; ;;
pascal@24476 27 ;; ;;
pascal@24476 28 ;; Known Bugs: ;;
pascal@24476 29 ;; ~~~~~~~~~~~ ;;
pascal@24476 30 ;; - All bugs are fixed as far as I know. The boot sector has been tested ;;
pascal@24476 31 ;; on my HDD and an 8GB USB stick. ;;
pascal@24476 32 ;; ;;
pascal@24476 33 ;; ;;
pascal@24476 34 ;; Memory Layout: ;;
pascal@24476 35 ;; ~~~~~~~~~~~~~~ ;;
pascal@24476 36 ;; The diagram below shows the typical memory layout. The actual location ;;
pascal@24476 37 ;; of the boot sector and its stack may be lower than A0000H if the BIOS ;;
pascal@24476 38 ;; reserves memory for its Extended BIOS Data Area just below A0000H and ;;
pascal@24476 39 ;; reports less than 640 KB of RAM via its Int 12H function. ;;
pascal@24476 40 ;; ;;
pascal@24476 41 ;; physical address ;;
pascal@24476 42 ;; +------------------------+ 00000H ;;
pascal@24476 43 ;; | Interrupt Vector Table | ;;
pascal@24476 44 ;; +------------------------+ 00400H ;;
pascal@24476 45 ;; | BIOS Data Area | ;;
pascal@24476 46 ;; +------------------------+ 00500H ;;
pascal@24476 47 ;; | PrtScr Status / Unused | ;;
pascal@24476 48 ;; +------------------------+ 00600H ;;
pascal@24476 49 ;; | Loaded Image | ;;
pascal@24476 50 ;; +------------------------+ nnnnnH ;;
pascal@24476 51 ;; | Available Memory | ;;
pascal@24525 52 ;; +------------------------+ A0000H - 2KB ;;
pascal@24476 53 ;; | Boot Sector | ;;
pascal@24525 54 ;; +------------------------+ A0000H - 1.5KB ;;
pascal@24525 55 ;; | 1.5KB Boot Stack | ;;
pascal@24476 56 ;; +------------------------+ A0000H ;;
pascal@24476 57 ;; | Video RAM | ;;
pascal@24476 58 ;; ;;
pascal@24476 59 ;; ;;
pascal@24476 60 ;; Boot Image Startup (register values): ;;
pascal@24476 61 ;; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ;;
pascal@24476 62 ;; dl = BIOS boot drive number (e.g. 80H) ;;
pascal@24476 63 ;; cs:ip = program entry point ;;
pascal@24476 64 ;; ss:sp = program stack (don't confuse with boot sector's stack) ;;
pascal@24476 65 ;; COM program defaults: cs = ds = es = ss = 50h, sp = 0, ip = 100h ;;
pascal@24476 66 ;; EXE program defaults: ds = es = EXE data - 10h (fake MS-DOS psp), ;;
pascal@24476 67 ;; ax = 0ffffh (both FCB in the PSP don't have a valid drive identifier), ;;
pascal@24476 68 ;; cs:ip and ss:sp depends on EXE header ;;
pascal@24476 69 ;; Magic numbers: ;;
pascal@24476 70 ;; si = 16381 (prime number 2**14-3) ;;
pascal@24476 71 ;; di = 32749 (prime number 2**15-19) ;;
pascal@24476 72 ;; bp = 65521 (prime number 2**16-15) ;;
pascal@24476 73 ;; The magic numbers let the program know whether it has been loaded by ;;
pascal@24476 74 ;; this boot sector or by MS-DOS, which may be handy for universal, bare- ;;
pascal@24476 75 ;; metal and MS-DOS programs. ;;
pascal@24476 76 ;; ;;
pascal@24476 77 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 78
pascal@24491 79 %define bx(label) bx+label-boot
pascal@24491 80
pascal@24476 81 [BITS 16]
pascal@24476 82
pascal@24478 83 ImageLoadSeg equ 60h ; <=07Fh because of "push byte ImageLoadSeg" instructions
pascal@24525 84 StackSize equ 1536
pascal@24476 85
pascal@24476 86 [SECTION .text]
pascal@24476 87 [ORG 0]
pascal@24476 88
pascal@24476 89 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 90 ;; Boot sector starts here ;;
pascal@24476 91 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 92
pascal@24491 93 boot:
pascal@24491 94 HiLBA equ boot+0
pascal@24476 95 jmp short start ; MS-DOS/Windows checks for this jump
pascal@24476 96 nop
pascal@24476 97 bsOemName DB "BootProg" ; 0x03
pascal@24476 98
pascal@24476 99 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 100 ;; BPB1 starts here ;;
pascal@24476 101 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 102
pascal@24479 103 bpbBytesPerSector DW 0 ; 0x0B
pascal@24479 104 bpbSectorsPerCluster DB 0 ; 0x0D
pascal@24479 105 bpbReservedSectors DW 0 ; 0x0E
pascal@24479 106 bpbNumberOfFATs DB 0 ; 0x10
pascal@24479 107 bpbRootEntries DW 0 ; 0x11
pascal@24479 108 bpbTotalSectors DW 0 ; 0x13
pascal@24479 109 bpbMedia DB 0 ; 0x15
pascal@24479 110 bpbSectorsPerFAT DW 0 ; 0x16
pascal@24479 111 bpbSectorsPerTrack DW 0 ; 0x18
pascal@24479 112 bpbHeadsPerCylinder DW 0 ; 0x1A
pascal@24479 113 bpbHiddenSectors DD 0 ; 0x1C
pascal@24479 114 bpbTotalSectorsBig DD 0 ; 0x20
pascal@24476 115
pascal@24476 116 ;;;;;;;;;;;;;;;;;;;;
pascal@24476 117 ;; BPB1 ends here ;;
pascal@24476 118 ;;;;;;;;;;;;;;;;;;;;
pascal@24476 119
pascal@24476 120 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 121 ;; BPB2 starts here ;;
pascal@24476 122 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 123
pascal@24479 124 bsSectorsPerFAT32 DD 0 ; 0x24
pascal@24479 125 bsExtendedFlags DW 0 ; 0x28
pascal@24479 126 bsFSVersion DW 0 ; 0x2A
pascal@24479 127 bsRootDirectoryClusterNo DD 0 ; 0x2C
pascal@24479 128 bsFSInfoSectorNo DW 0 ; 0x30
pascal@24479 129 bsBackupBootSectorNo DW 0 ; 0x32
pascal@24479 130 bsreserved times 12 DB 0 ; 0x34
pascal@24479 131 bsDriveNumber DB 0 ; 0x40
pascal@24479 132 bsreserved1 DB 0 ; 0x41
pascal@24479 133 bsExtendedBootSignature DB 0 ; 0x42
pascal@24479 134 bsVolumeSerialNumber DD 0 ; 0x43
pascal@24476 135 bsVolumeLabel DB "NO NAME " ; 0x47
pascal@24476 136 bsFileSystemName DB "FAT32 " ; 0x52
pascal@24476 137
pascal@24476 138 ;;;;;;;;;;;;;;;;;;;;
pascal@24476 139 ;; BPB2 ends here ;;
pascal@24476 140 ;;;;;;;;;;;;;;;;;;;;
pascal@24476 141
pascal@24476 142 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 143 ;; Boot sector code starts here ;;
pascal@24476 144 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 145
pascal@24476 146 start:
pascal@24476 147 cld
pascal@24476 148
pascal@24476 149 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 150 ;; How much RAM is there? ;;
pascal@24476 151 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 152
pascal@24476 153 int 12h ; get conventional memory size (in KBs)
pascal@24525 154 dec ax
pascal@24525 155 dec ax ; reserve 2K bytes for the code and the stack
pascal@24525 156 mov cx, 106h
pascal@24525 157 shl ax, cl ; and convert it to 16-byte paragraphs
pascal@24476 158
pascal@24476 159 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 160 ;; Reserve memory for the boot sector and its stack ;;
pascal@24476 161 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 162
pascal@24525 163 mov es, ax ; cs:0 = ds:0 = ss:0 -> top - 512 - StackSize
pascal@24525 164 mov ss, ax
pascal@24525 165 mov sp, 512+StackSize ; bytes 0-511 are reserved for the boot code
pascal@24476 166
pascal@24476 167 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 168 ;; Copy ourselves to top of memory ;;
pascal@24476 169 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 170
pascal@24476 171 mov si, 7C00h
pascal@24476 172 xor di, di
pascal@24476 173 mov ds, di
pascal@24478 174 rep movsw
pascal@24476 175
pascal@24476 176 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 177 ;; Jump to the copy ;;
pascal@24476 178 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 179
pascal@24476 180 push es
pascal@24478 181 push byte main
pascal@24476 182 retf
pascal@24476 183
pascal@24476 184 main:
pascal@24476 185 push cs
pascal@24476 186 pop ds
pascal@24476 187
pascal@24491 188 xor bx, bx
pascal@24491 189 mov [bx(bsDriveNumber)], dx ; store BIOS boot drive number
pascal@24476 190
pascal@24491 191 and byte [bx(bsRootDirectoryClusterNo+3)], 0Fh ; mask cluster value
pascal@24491 192 mov esi, [bx(bsRootDirectoryClusterNo)] ; esi=cluster # of root dir
pascal@24476 193
pascal@24476 194 RootDirReadContinue:
pascal@24478 195 push byte ImageLoadSeg
pascal@24478 196 pop es
pascal@24478 197 call ReadCluster ; read one cluster of root dir
pascal@24478 198 pushf ; save carry="not last cluster" flag
pascal@24476 199
pascal@24476 200 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 201 ;; Look for the COM/EXE file to load and run ;;
pascal@24476 202 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 203
pascal@24476 204 xor di, di ; es:di -> root entries array
pascal@24476 205
pascal@24476 206 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24478 207 ;; Looks for a file/dir by its name ;;
pascal@24476 208 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24478 209 ;; Input: DS:SI -> file name (11 chars) ;;
pascal@24478 210 ;; ES:DI -> root directory array ;;
pascal@24478 211 ;; DX = number of root entries ;;
pascal@24525 212 ;; BP = paragraphs in sector ;;
pascal@24476 213 ;; Output: ESI = cluster number ;;
pascal@24476 214 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 215
pascal@24478 216 FindName:
pascal@24476 217 FindNameCycle:
pascal@24525 218 cmp byte [es:di], bh
pascal@24478 219 je ErrFind ; end of root directory (NULL entry found)
pascal@24478 220 FindNameNotEnd:
pascal@24478 221 pusha
pascal@24525 222 mov cl, 11
pascal@24525 223 mov si, ProgramName ; ds:si -> program name
pascal@24476 224 repe cmpsb
pascal@24525 225 je FindNameFound
pascal@24478 226 popa
pascal@24525 227 add di, byte 32
pascal@24476 228 dec bp
pascal@24476 229 dec bp
pascal@24476 230 jnz FindNameCycle ; next root entry
pascal@24478 231 popf ; restore carry="not last cluster" flag
pascal@24476 232 jc RootDirReadContinue ; continue to the next root dir cluster
pascal@24478 233 ErrFind:
pascal@24478 234 call Error ; end of root directory (dir end reached)
pascal@24476 235 db "File not found."
pascal@24476 236 FindNameFound:
pascal@24525 237 push word [es:di+14h-11]
pascal@24525 238 push word [es:di+1Ah-11]
pascal@24478 239 pop esi ; esi = cluster no. cx = 0
pascal@24476 240
pascal@24525 241 dec dword [es:di+1Ch-11] ; load ((n - 1)/256)*16 +1 paragraphs
pascal@24525 242 imul di, [es:di+1Ch+1-11], byte 16 ; file size in paragraphs (full pages)
pascal@24476 243
pascal@24476 244 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 245 ;; Load the entire file ;;
pascal@24476 246 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 247
pascal@24476 248 push es
pascal@24476 249 FileReadContinue:
pascal@24476 250 push di
pascal@24478 251 call ReadCluster ; read one cluster of root dir
pascal@24476 252 mov di, es
pascal@24478 253 add di, bp
pascal@24478 254 mov es, di ; es:bx updated
pascal@24476 255 pop di
pascal@24478 256
pascal@24476 257 sub di, bp
pascal@24476 258 jae FileReadContinue
pascal@24476 259 pop bp
pascal@24476 260
pascal@24476 261 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 262 ;; Type detection, .COM or .EXE? ;;
pascal@24476 263 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 264
pascal@24476 265 mov ds, bp ; bp=ds=seg the file is loaded to
pascal@24535 266
pascal@24476 267 add bp, [bx+08h] ; bp = image base
pascal@24476 268 mov ax, [bx+06h] ; ax = reloc items
pascal@24476 269 mov di, [bx+18h] ; di = reloc table pointer
pascal@24476 270
pascal@24476 271 cmp word [bx], 5A4Dh ; "MZ" signature?
pascal@24476 272 je RelocateEXE ; yes, it's an EXE program
pascal@24476 273
pascal@24476 274 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 275 ;; Setup and run a .COM program ;;
pascal@24535 276 ;; Set CS=DS=ES=SS SP=0 IP=100h ;;
pascal@24535 277 ;; AX=0ffffh BX=0 CX=0 DX=drive ;;
pascal@24476 278 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 279
pascal@24535 280 mov ax, 0ffffh ; both FCB in the PSP don't have a valid drive identifier
pascal@24535 281 mov di, 100h ; ip
pascal@24476 282 mov bp, ImageLoadSeg-10h ; "org 100h" stuff :)
pascal@24476 283 mov ss, bp
pascal@24476 284 xor sp, sp
pascal@24476 285 push bp ; cs, ds and es
pascal@24476 286 jmp short Run
pascal@24476 287
pascal@24476 288 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 289 ;; Relocate, setup and run a .EXE program ;;
pascal@24476 290 ;; Set CS:IP, SS:SP, DS, ES and AX according ;;
pascal@24476 291 ;; to wiki.osdev.org/MZ#Initial_Program_State ;;
pascal@24535 292 ;; AX=0ffffh BX=0 CX=0 DX=drive ;;
pascal@24476 293 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 294
pascal@24476 295 ReloCycle:
pascal@24476 296 add [di+2], bp ; item seg (abs)
pascal@24476 297 les si, [di] ; si = item ofs, es = item seg
pascal@24476 298 add [es:si], bp ; fixup
pascal@24525 299 scasw ; di += 2
pascal@24525 300 scasw ; point to next entry
pascal@24476 301
pascal@24476 302 RelocateEXE:
pascal@24476 303 dec ax ; 32768 max (128KB table)
pascal@24476 304 jns ReloCycle ; leave with ax=0ffffh: both FCB in the
pascal@24476 305 ; PSP don't have a valid drive identifier
pascal@24476 306 les si, [bx+0Eh]
pascal@24476 307 add si, bp
pascal@24476 308 mov ss, si ; ss for EXE
pascal@24476 309 mov sp, es ; sp for EXE
pascal@24476 310
pascal@24476 311 lea si, [bp-10h] ; ds and es both point to the segment
pascal@24476 312 push si ; containing the PSP structure
pascal@24476 313
pascal@24476 314 add bp, [bx+16h] ; cs for EXE
pascal@24535 315 mov di, [bx+14h] ; ip for EXE
pascal@24476 316 Run:
pascal@24476 317 pop ds
pascal@24476 318 push bp
pascal@24535 319 push di
pascal@24476 320 push ds
pascal@24476 321 pop es
pascal@24476 322
pascal@24476 323 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 324 ;; Set the magic numbers so the program knows that it ;;
pascal@24476 325 ;; has been loaded by this bootsector and not by MS-DOS ;;
pascal@24476 326 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 327 mov si, 16381 ; prime number 2**14-3
pascal@24476 328 mov di, 32749 ; prime number 2**15-19
pascal@24476 329 mov bp, 65521 ; prime number 2**16-15
pascal@24476 330
pascal@24476 331 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 332 ;; All done, transfer control to the program now ;;
pascal@24476 333 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 334 retf
pascal@24476 335
pascal@24525 336 ReadCluster:
pascal@24525 337 mov bp, [bx(bpbBytesPerSector)]
pascal@24525 338 shr bp, 4 ; bp = paragraphs per sector
pascal@24535 339 add eax, byte 1 ; adjust LBA for next sector
pascal@24525 340 inc cx
pascal@24525 341 loop ReadSectorLBA
pascal@24525 342
pascal@24478 343 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24478 344 ;; Reads a FAT32 cluster ;;
pascal@24478 345 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24478 346 ;; Inout: ES:BX -> buffer ;;
pascal@24478 347 ;; ESI = cluster no ;;
pascal@24478 348 ;; Output: ESI = next cluster ;;
pascal@24525 349 ;; BP -> para / sector ;;
pascal@24478 350 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 351
pascal@24525 352 imul ax, bp, byte 2 ; ax=# of FAT32 entries per sector
pascal@24478 353 cwde
pascal@24525 354 lea edi, [esi-2] ; esi=cluster #
pascal@24476 355 xchg eax, esi
pascal@24476 356 cdq
pascal@24478 357 div esi ; eax=FAT sector #, edx=entry # in sector
pascal@24476 358
pascal@24525 359 imul si, dx, byte 4 ; si=entry # in sector, clear C
pascal@24491 360 mov word [bx(HiLBA)], bx
pascal@24478 361 call ReadSectorLBAabsolute ; read 1 FAT32 sector
pascal@24476 362
pascal@24478 363 and byte [es:si+3], 0Fh ; mask cluster value
pascal@24478 364 mov esi, [es:si] ; esi=next cluster #
pascal@24476 365
pascal@24525 366 movzx eax, byte [bx(bpbNumberOfFATs)]
pascal@24525 367 mul dword [bx(bsSectorsPerFAT32)]
pascal@24525 368 mov word [bx(HiLBA)], dx
pascal@24525 369
pascal@24525 370 xchg eax, edi
pascal@24491 371 movzx ecx, byte [bx(bpbSectorsPerCluster)]
pascal@24491 372 mul ecx ; edx:eax=sector number in data area
pascal@24476 373
pascal@24525 374 add eax, edi
pascal@24491 375 adc word [bx(HiLBA)], dx
pascal@24476 376
pascal@24478 377 ReadSectorLBAabsolute:
pascal@24525 378 mov dx, word [bx(bpbReservedSectors)]
pascal@24478 379 add eax, edx
pascal@24491 380 adc word [bx(HiLBA)], bx
pascal@24491 381 add eax, [bx(bpbHiddenSectors)]
pascal@24476 382
pascal@24478 383 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24478 384 ;; Reads a sector using BIOS Int 13h fn 42h ;;
pascal@24478 385 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24478 386 ;; Input: EAX = LBA ;;
pascal@24478 387 ;; CX = sector count ;;
pascal@24478 388 ;; ES:BX -> buffer address ;;
pascal@24478 389 ;; Output: CF = 0 if no more sectors ;;
pascal@24478 390 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 391
pascal@24476 392 ReadSectorLBA:
pascal@24535 393 adc word [bx(HiLBA)], bx
pascal@24535 394 mov dx, [bx(bsDriveNumber)] ; restore BIOS boot drive number
pascal@24476 395 pusha
pascal@24476 396
pascal@24478 397 push bx
pascal@24491 398 push word [bx(HiLBA)] ; 48-bit LBA
pascal@24478 399 push eax
pascal@24476 400 push es
pascal@24476 401 push bx
pascal@24478 402 push byte 1 ; sector count word = 1
pascal@24525 403 push byte 16 ; packet size byte = 16, reserved byte = 0
pascal@24525 404
pascal@24525 405 ReadSectorLBARetry:
pascal@24525 406 mov si, sp
pascal@24478 407 mov ah, 42h ; ah = 42h = extended read function no.
pascal@24478 408 int 13h ; extended read sectors (DL, DS:SI)
pascal@24478 409 jnc ReadSuccess ; CF = 0 if no error
pascal@24476 410
pascal@24525 411 cbw ; ah = 0 = reset function
pascal@24476 412 int 13h ; reset drive (DL)
pascal@24476 413
pascal@24525 414 dec bp
pascal@24525 415 jnz ReadSectorLBARetry
pascal@24525 416
pascal@24476 417 call Error
pascal@24476 418 db "Read error."
pascal@24476 419
pascal@24478 420 ReadSuccess:
pascal@24476 421
pascal@24476 422 popa ; sp += 16
pascal@24478 423
pascal@24478 424 popa
pascal@24478 425
pascal@24476 426 stc
pascal@24478 427 loop ReadSectorNext
pascal@24476 428
pascal@24478 429 cmp esi, 0FFFFFF8h ; carry=0 if last cluster, and carry=1 otherwise
pascal@24476 430
pascal@24478 431 ReadSectorNext:
pascal@24476 432 ret
pascal@24476 433
pascal@24476 434 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 435 ;; Error Messaging Code ;;
pascal@24476 436 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 437
pascal@24476 438 Error:
pascal@24476 439 pop si
pascal@24478 440 puts:
pascal@24476 441 mov ah, 0Eh
pascal@24476 442 mov bl, 7
pascal@24476 443 lodsb
pascal@24476 444 int 10h
pascal@24478 445 cmp al, '.'
pascal@24478 446 jne puts
pascal@24476 447 cbw
pascal@24535 448 int 16h ; wait for a key...
pascal@24535 449 int 19h ; bootstrap
pascal@24525 450
pascal@24525 451 Stop:
pascal@24525 452 hlt
pascal@24525 453 jmp short Stop
pascal@24476 454
pascal@24476 455 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 456 ;; Fill free space with zeroes ;;
pascal@24476 457 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 458
pascal@24476 459 times (512-13-($-$$)) db 0
pascal@24476 460
pascal@24476 461 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 462 ;; Name of the file to load and run ;;
pascal@24476 463 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 464
pascal@24476 465 ProgramName db "STARTUP BIN" ; name and extension each must be
pascal@24476 466 ; padded with spaces (11 bytes total)
pascal@24476 467
pascal@24476 468 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 469 ;; End of the sector ID ;;
pascal@24476 470 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 471
pascal@24476 472 dw 0AA55h ; BIOS checks for this ID