wok annotate BootProg/stuff/boot32.asm @ rev 25467

Up gnumeric (1.12.53)
author Pascal Bellard <pascal.bellard@slitaz.org>
date Mon Oct 03 08:28:51 2022 +0000 (21 months ago)
parents 81fc994927a6
children 2155b2665e26
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@25460 20 ;; Its maximum size can be up to 637KB 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@25460 52 ;; +------------------------+ A0000H - 1KB ;;
pascal@24476 53 ;; | Boot Sector | ;;
pascal@25460 54 ;; +------------------------+ A0000H - 0.5KB ;;
pascal@25460 55 ;; | 0.5KB 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@24945 62 ;; ax = 0ffffh (both FCB in the PSP don't have a valid drive identifier), ;;
pascal@25454 63 ;; bx = 0, dl = BIOS boot drive number (e.g. 0, 80H) ;;
pascal@24476 64 ;; cs:ip = program entry point ;;
pascal@24476 65 ;; ss:sp = program stack (don't confuse with boot sector's stack) ;;
pascal@24476 66 ;; COM program defaults: cs = ds = es = ss = 50h, sp = 0, ip = 100h ;;
pascal@24476 67 ;; EXE program defaults: ds = es = EXE data - 10h (fake MS-DOS psp), ;;
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@24945 76 ;; The command line contains no arguments. ;;
pascal@24476 77 ;; ;;
pascal@24476 78 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 79
pascal@24491 80 %define bx(label) bx+label-boot
pascal@25449 81 %define si(label) si+label-boot
pascal@25449 82 ClusterMask equ 1 ; +9 bytes
pascal@25460 83 NullEntryCheck equ 1 ; +5 bytes
pascal@25449 84 ReadRetry equ 1 ; +7 bytes
pascal@25458 85 LBA48bits equ 1 ; +15 bytes
pascal@25449 86 CHSsupport equ 1 ; +27 bytes
pascal@25458 87 CHSupTo8GB equ 1 ; +11 bytes
pascal@25458 88 CHSupTo32MB equ 1 ; +7 bytes
pascal@25458 89 SectorOf512Bytes equ 1 ; -5 bytes
pascal@25458 90 Always2FATs equ 0 ; -4 bytes
pascal@25467 91 CheckAttrib equ 0 ; +6 bytes
pascal@24491 92
pascal@24476 93 [BITS 16]
pascal@24476 94
pascal@24478 95 ImageLoadSeg equ 60h ; <=07Fh because of "push byte ImageLoadSeg" instructions
pascal@25460 96 StackSize equ 512
pascal@24476 97
pascal@24476 98 [SECTION .text]
pascal@24476 99 [ORG 0]
pascal@24476 100
pascal@24476 101 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 102 ;; Boot sector starts here ;;
pascal@24476 103 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 104
pascal@24491 105 boot:
pascal@25458 106 DriveNumber equ boot+0
pascal@25458 107 HiLBA equ boot+2
pascal@24476 108 jmp short start ; MS-DOS/Windows checks for this jump
pascal@24476 109 nop
pascal@24476 110 bsOemName DB "BootProg" ; 0x03
pascal@24476 111
pascal@24476 112 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 113 ;; BPB1 starts here ;;
pascal@24476 114 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 115
pascal@24479 116 bpbBytesPerSector DW 0 ; 0x0B
pascal@24479 117 bpbSectorsPerCluster DB 0 ; 0x0D
pascal@24479 118 bpbReservedSectors DW 0 ; 0x0E
pascal@24479 119 bpbNumberOfFATs DB 0 ; 0x10
pascal@24479 120 bpbRootEntries DW 0 ; 0x11
pascal@24479 121 bpbTotalSectors DW 0 ; 0x13
pascal@24479 122 bpbMedia DB 0 ; 0x15
pascal@24479 123 bpbSectorsPerFAT DW 0 ; 0x16
pascal@24479 124 bpbSectorsPerTrack DW 0 ; 0x18
pascal@24479 125 bpbHeadsPerCylinder DW 0 ; 0x1A
pascal@24479 126 bpbHiddenSectors DD 0 ; 0x1C
pascal@24479 127 bpbTotalSectorsBig DD 0 ; 0x20
pascal@24476 128
pascal@24476 129 ;;;;;;;;;;;;;;;;;;;;
pascal@24476 130 ;; BPB1 ends here ;;
pascal@24476 131 ;;;;;;;;;;;;;;;;;;;;
pascal@24476 132
pascal@24476 133 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 134 ;; BPB2 starts here ;;
pascal@24476 135 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 136
pascal@24479 137 bsSectorsPerFAT32 DD 0 ; 0x24
pascal@24479 138 bsExtendedFlags DW 0 ; 0x28
pascal@24479 139 bsFSVersion DW 0 ; 0x2A
pascal@24479 140 bsRootDirectoryClusterNo DD 0 ; 0x2C
pascal@24479 141 bsFSInfoSectorNo DW 0 ; 0x30
pascal@24479 142 bsBackupBootSectorNo DW 0 ; 0x32
pascal@24479 143 bsreserved times 12 DB 0 ; 0x34
pascal@24479 144 bsDriveNumber DB 0 ; 0x40
pascal@24479 145 bsreserved1 DB 0 ; 0x41
pascal@24479 146 bsExtendedBootSignature DB 0 ; 0x42
pascal@24479 147 bsVolumeSerialNumber DD 0 ; 0x43
pascal@25458 148 bsVolumeLabel times 11 DB " " ; 0x47 "NO NAME "
pascal@25458 149 bsFileSystemName times 8 DB " " ; 0x52 "FAT32 "
pascal@24476 150
pascal@24476 151 ;;;;;;;;;;;;;;;;;;;;
pascal@24476 152 ;; BPB2 ends here ;;
pascal@24476 153 ;;;;;;;;;;;;;;;;;;;;
pascal@24476 154
pascal@24476 155 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 156 ;; Boot sector code starts here ;;
pascal@24476 157 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 158
pascal@24476 159 start:
pascal@24476 160 cld
pascal@24476 161
pascal@24476 162 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 163 ;; How much RAM is there? ;;
pascal@24476 164 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 165
pascal@24476 166 int 12h ; get conventional memory size (in KBs)
pascal@25460 167 dec ax ; reserve 1K bytes for the code and the stack
pascal@24525 168 mov cx, 106h
pascal@24525 169 shl ax, cl ; and convert it to 16-byte paragraphs
pascal@24476 170
pascal@24476 171 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 172 ;; Reserve memory for the boot sector and its stack ;;
pascal@24476 173 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 174
pascal@24525 175 mov es, ax ; cs:0 = ds:0 = ss:0 -> top - 512 - StackSize
pascal@24525 176 mov ss, ax
pascal@24525 177 mov sp, 512+StackSize ; bytes 0-511 are reserved for the boot code
pascal@24476 178
pascal@24476 179 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 180 ;; Copy ourselves to top of memory ;;
pascal@24476 181 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 182
pascal@24476 183 mov si, 7C00h
pascal@24476 184 xor di, di
pascal@24476 185 mov ds, di
pascal@25449 186 push es
pascal@25449 187 mov [si(DriveNumber)], dx ; store BIOS boot drive number
pascal@24478 188 rep movsw
pascal@24476 189
pascal@24476 190 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 191 ;; Jump to the copy ;;
pascal@24476 192 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 193
pascal@25450 194 push byte main
pascal@24476 195 retf
pascal@24476 196
pascal@24476 197 main:
pascal@24476 198 push cs
pascal@24476 199 pop ds
pascal@24476 200
pascal@25449 201 xor ebx, ebx
pascal@24476 202
pascal@25449 203 %if ClusterMask != 0
pascal@24491 204 and byte [bx(bsRootDirectoryClusterNo+3)], 0Fh ; mask cluster value
pascal@25449 205 %endif
pascal@24491 206 mov esi, [bx(bsRootDirectoryClusterNo)] ; esi=cluster # of root dir
pascal@24476 207
pascal@24478 208 push byte ImageLoadSeg
pascal@24478 209 pop es
pascal@25449 210
pascal@25449 211 RootDirReadContinue:
pascal@25458 212 call ReadClusterSector ; read one sector of the root dir
pascal@24476 213
pascal@24476 214 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 215 ;; Look for the COM/EXE file to load and run ;;
pascal@24476 216 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 217
pascal@24476 218 xor di, di ; es:di -> root entries array
pascal@24476 219
pascal@24476 220 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24478 221 ;; Looks for a file/dir by its name ;;
pascal@24476 222 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24478 223 ;; Input: DS:SI -> file name (11 chars) ;;
pascal@24478 224 ;; ES:DI -> root directory array ;;
pascal@24525 225 ;; BP = paragraphs in sector ;;
pascal@24476 226 ;; Output: ESI = cluster number ;;
pascal@24476 227 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 228
pascal@24476 229 FindNameCycle:
pascal@25449 230 %if NullEntryCheck != 0
pascal@24525 231 cmp byte [es:di], bh
pascal@24478 232 je ErrFind ; end of root directory (NULL entry found)
pascal@25449 233 %endif
pascal@24478 234 pusha
pascal@25454 235 mov cl, NameLength
pascal@24525 236 mov si, ProgramName ; ds:si -> program name
pascal@24476 237 repe cmpsb
pascal@25467 238 %if CheckAttrib != 0
pascal@25467 239 VolumeLabel equ 8
pascal@25467 240 SubDirectory equ 10h
pascal@25467 241 jnz SkipFindName
pascal@25467 242 test byte [es:di], VolumeLabel+SubDirectory
pascal@25467 243 SkipFindName:
pascal@25467 244 %endif
pascal@24525 245 je FindNameFound
pascal@24478 246 popa
pascal@24525 247 add di, byte 32
pascal@24476 248 dec bp
pascal@24476 249 dec bp
pascal@24476 250 jnz FindNameCycle ; next root entry
pascal@25458 251 loop RootDirReadContinue ; next sector in cluster
pascal@25458 252 cmp esi, 0FFFFFF6h ; carry=0 if last cluster, and carry=1 otherwise
pascal@25458 253 jnc RootDirReadContinue ; continue to the next root dir cluster
pascal@24478 254 ErrFind:
pascal@24478 255 call Error ; end of root directory (dir end reached)
pascal@24476 256 db "File not found."
pascal@24476 257 FindNameFound:
pascal@24525 258 push word [es:di+14h-11]
pascal@24525 259 push word [es:di+1Ah-11]
pascal@24478 260 pop esi ; esi = cluster no. cx = 0
pascal@24476 261
pascal@24525 262 dec dword [es:di+1Ch-11] ; load ((n - 1)/256)*16 +1 paragraphs
pascal@24525 263 imul di, [es:di+1Ch+1-11], byte 16 ; file size in paragraphs (full pages)
pascal@24476 264
pascal@24476 265 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 266 ;; Load the entire file ;;
pascal@24476 267 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 268
pascal@24476 269 push es
pascal@24476 270 FileReadContinue:
pascal@24476 271 push di
pascal@25458 272 call ReadClusterSector ; read one sector of the boot file
pascal@25458 273 dec cx
pascal@24476 274 mov di, es
pascal@24478 275 add di, bp
pascal@24478 276 mov es, di ; es:bx updated
pascal@24476 277 pop di
pascal@24478 278
pascal@24476 279 sub di, bp
pascal@24476 280 jae FileReadContinue
pascal@24943 281 xor ax, ax
pascal@24476 282 pop bp
pascal@24476 283
pascal@24476 284 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 285 ;; Type detection, .COM or .EXE? ;;
pascal@24476 286 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 287
pascal@24476 288 mov ds, bp ; bp=ds=seg the file is loaded to
pascal@24535 289
pascal@24476 290 add bp, [bx+08h] ; bp = image base
pascal@24476 291 mov di, [bx+18h] ; di = reloc table pointer
pascal@24476 292
pascal@24476 293 cmp word [bx], 5A4Dh ; "MZ" signature?
pascal@24476 294 je RelocateEXE ; yes, it's an EXE program
pascal@24476 295
pascal@24476 296 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 297 ;; Setup and run a .COM program ;;
pascal@24535 298 ;; Set CS=DS=ES=SS SP=0 IP=100h ;;
pascal@25454 299 ;; AX=0ffffh BX=0 DX=drive and ;;
pascal@25454 300 ;; cmdline=void ;;
pascal@24476 301 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 302
pascal@24535 303 mov di, 100h ; ip
pascal@24476 304 mov bp, ImageLoadSeg-10h ; "org 100h" stuff :)
pascal@24476 305 mov ss, bp
pascal@24476 306 xor sp, sp
pascal@24476 307 push bp ; cs, ds and es
pascal@24476 308 jmp short Run
pascal@24476 309
pascal@24476 310 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 311 ;; Relocate, setup and run a .EXE program ;;
pascal@24476 312 ;; Set CS:IP, SS:SP, DS, ES and AX according ;;
pascal@24476 313 ;; to wiki.osdev.org/MZ#Initial_Program_State ;;
pascal@25454 314 ;; AX=0ffffh BX=0 DX=drive cmdline=void ;;
pascal@24476 315 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 316
pascal@24476 317 ReloCycle:
pascal@24476 318 add [di+2], bp ; item seg (abs)
pascal@24476 319 les si, [di] ; si = item ofs, es = item seg
pascal@24476 320 add [es:si], bp ; fixup
pascal@24525 321 scasw ; di += 2
pascal@24525 322 scasw ; point to next entry
pascal@24476 323
pascal@24476 324 RelocateEXE:
pascal@24942 325 dec word [bx+06h] ; reloc items, 32768 max (128KB table)
pascal@24942 326 jns ReloCycle
pascal@24942 327
pascal@24945 328 les si, [bx+0Eh]
pascal@24945 329 add si, bp
pascal@24945 330 mov ss, si ; ss for EXE
pascal@24945 331 mov sp, es ; sp for EXE
pascal@24476 332
pascal@24476 333 lea si, [bp-10h] ; ds and es both point to the segment
pascal@24476 334 push si ; containing the PSP structure
pascal@24476 335
pascal@24476 336 add bp, [bx+16h] ; cs for EXE
pascal@24535 337 mov di, [bx+14h] ; ip for EXE
pascal@24476 338 Run:
pascal@24476 339 pop ds
pascal@24476 340 push bp
pascal@24535 341 push di
pascal@24476 342 push ds
pascal@24476 343 pop es
pascal@24942 344 mov [80h], ax ; clear cmdline
pascal@24942 345 dec ax ; both FCB in the PSP don't have a valid drive identifier
pascal@24476 346
pascal@24476 347 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 348 ;; Set the magic numbers so the program knows that it ;;
pascal@24476 349 ;; has been loaded by this bootsector and not by MS-DOS ;;
pascal@24476 350 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 351 mov si, 16381 ; prime number 2**14-3
pascal@24476 352 mov di, 32749 ; prime number 2**15-19
pascal@24476 353 mov bp, 65521 ; prime number 2**16-15
pascal@24476 354
pascal@24476 355 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 356 ;; All done, transfer control to the program now ;;
pascal@24476 357 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 358 retf
pascal@24476 359
pascal@25458 360 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@25458 361 ;; Error Messaging Code ;;
pascal@25458 362 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@25458 363
pascal@25458 364 Error:
pascal@25458 365 pop si
pascal@25458 366 puts:
pascal@25458 367 mov ah, 0Eh
pascal@25458 368 mov bl, 7
pascal@25458 369 lodsb
pascal@25458 370 int 10h
pascal@25458 371 cmp al, '.'
pascal@25458 372 jne puts
pascal@25458 373 cbw
pascal@25458 374 int 16h ; wait for a key...
pascal@25458 375 int 19h ; bootstrap
pascal@25458 376
pascal@25458 377 Stop:
pascal@25458 378 hlt
pascal@25458 379 jmp short Stop
pascal@25458 380
pascal@25458 381 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@25458 382 ;; Reads a FAT32 sector ;;
pascal@25458 383 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@25458 384 ;; Inout: ES:BX -> buffer ;;
pascal@25458 385 ;; EAX = prev sector ;;
pascal@25458 386 ;; CX = rem sectors in cluster ;;
pascal@25458 387 ;; ESI = next cluster ;;
pascal@25458 388 ;; Output: EAX = current sector ;;
pascal@25458 389 ;; CX = rem sectors in cluster ;;
pascal@25458 390 ;; ESI = next cluster ;;
pascal@25458 391 ;; BP -> para / sector ;;
pascal@25458 392 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@25458 393
pascal@25458 394 ReadClusterSector:
pascal@25458 395 %if SectorOf512Bytes != 0
pascal@25458 396 mov bp, 32 ; bp = paragraphs per sector
pascal@25458 397 %else
pascal@24525 398 mov bp, [bx(bpbBytesPerSector)]
pascal@24525 399 shr bp, 4 ; bp = paragraphs per sector
pascal@25458 400 %endif
pascal@25449 401 mov dx, 1 ; adjust LBA for next sector
pascal@24525 402 inc cx
pascal@24525 403 loop ReadSectorLBA
pascal@24525 404
pascal@25449 405 mul ebx ; edx:eax = 0
pascal@25458 406 %if SectorOf512Bytes != 0
pascal@25458 407 mov al, 128 ; ax=# of FAT32 entries per sector
pascal@25458 408 %else
pascal@24945 409 imul ax, bp, byte 4 ; ax=# of FAT32 entries per sector
pascal@25458 410 %endif
pascal@24525 411 lea edi, [esi-2] ; esi=cluster #
pascal@24476 412 xchg eax, esi
pascal@24478 413 div esi ; eax=FAT sector #, edx=entry # in sector
pascal@24476 414
pascal@24525 415 imul si, dx, byte 4 ; si=entry # in sector, clear C
pascal@25449 416 %if LBA48bits != 0
pascal@25458 417 xor dx, dx
pascal@25449 418 %endif
pascal@25458 419 call ReadSectorLBAfromFAT ; read 1 FAT32 sector
pascal@24476 420
pascal@25449 421 %if ClusterMask != 0
pascal@24478 422 and byte [es:si+3], 0Fh ; mask cluster value
pascal@25449 423 %endif
pascal@24478 424 mov esi, [es:si] ; esi=next cluster #
pascal@24476 425
pascal@25458 426 %if Always2FATs != 0
pascal@25458 427 imul eax, dword [bx(bsSectorsPerFAT32)], 2
pascal@25458 428 %else
pascal@24525 429 movzx eax, byte [bx(bpbNumberOfFATs)]
pascal@24525 430 mul dword [bx(bsSectorsPerFAT32)]
pascal@25458 431 %endif
pascal@24525 432
pascal@24525 433 xchg eax, edi
pascal@25454 434 movzx ecx, byte [bx(bpbSectorsPerCluster)] ; 8..128
pascal@24945 435 mul ecx ; edx:eax=sector number in data area
pascal@24525 436 add eax, edi
pascal@25458 437 %if LBA48bits != 0
pascal@25458 438 adc dx, bx
pascal@25458 439 %endif
pascal@24476 440
pascal@25458 441 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@25458 442 ;; Reads a sector form the start of FAT ;;
pascal@25458 443 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@25458 444
pascal@25458 445 ReadSectorLBAfromFAT:
pascal@25458 446 add eax, [bx(bpbHiddenSectors)]
pascal@25449 447 %if LBA48bits != 0
pascal@25449 448 adc dx, bx
pascal@25449 449 mov word [bx(HiLBA)], dx
pascal@25449 450 %endif
pascal@25454 451 mov dx, [bx(bpbReservedSectors)]
pascal@24476 452
pascal@24478 453 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24478 454 ;; Reads a sector using BIOS Int 13h fn 42h ;;
pascal@24478 455 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24478 456 ;; Input: EAX = LBA ;;
pascal@24478 457 ;; CX = sector count ;;
pascal@24478 458 ;; ES:BX -> buffer address ;;
pascal@24478 459 ;; Output: CF = 0 if no more sectors ;;
pascal@24478 460 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 461
pascal@24476 462 ReadSectorLBA:
pascal@25449 463 add eax, edx
pascal@25449 464 %if LBA48bits != 0
pascal@24535 465 adc word [bx(HiLBA)], bx
pascal@25449 466 %endif
pascal@25449 467 mov dx, [bx(DriveNumber)] ; restore BIOS boot drive number
pascal@24476 468 pusha
pascal@24476 469
pascal@24478 470 push bx
pascal@25449 471 %if LBA48bits != 0
pascal@24491 472 push word [bx(HiLBA)] ; 48-bit LBA
pascal@25449 473 %else
pascal@25449 474 push bx
pascal@25449 475 %endif
pascal@24478 476 push eax
pascal@24476 477 push es
pascal@24476 478 push bx
pascal@24478 479 push byte 1 ; sector count word = 1
pascal@24525 480 push byte 16 ; packet size byte = 16, reserved byte = 0
pascal@24525 481
pascal@25449 482 %if CHSsupport != 0
pascal@25458 483 %if CHSupTo8GB != 0
pascal@25449 484 push eax
pascal@25449 485 pop cx ; save low LBA
pascal@25449 486 pop ax ; get high LBA
pascal@25449 487 cwd ; clear dx (assume LBA offset <1TB)
pascal@25449 488 idiv word [bx(bpbSectorsPerTrack)] ; up to 8GB disks, avoid divide error
pascal@25449 489
pascal@25449 490 xchg ax, cx ; restore low LBA, save high LBA / SPT
pascal@25458 491 %else
pascal@25449 492 ; Busybox mkdosfs creates fat32 for floppies.
pascal@25449 493 ; Floppies may support CHS only.
pascal@25458 494 %if CHSupTo32MB != 0
pascal@25458 495 xor dx, dx ; clear dx (LBA offset <32MB)
pascal@25458 496 %else
pascal@25449 497 cwd ; clear dx (LBA offset <16MB)
pascal@25458 498 %endif
pascal@25450 499 xor cx, cx ; high LBA / SPT = 0
pascal@25458 500 %endif
pascal@25449 501 idiv word [bx(bpbSectorsPerTrack)]
pascal@25449 502 ; ax = LBA / SPT
pascal@25449 503 ; dx = LBA % SPT = sector - 1
pascal@25449 504 inc dx
pascal@25449 505
pascal@25449 506 xchg cx, dx ; restore high LBA / SPT, save sector no.
pascal@25450 507 idiv word [bx(bpbHeadsPerCylinder)]
pascal@25449 508 ; ax = (LBA / SPT) / HPC = cylinder
pascal@25449 509 ; dx = (LBA / SPT) % HPC = head
pascal@25449 510
pascal@25458 511 xchg ch, al ; clear al
pascal@25449 512 ; ch = LSB 0...7 of cylinder no.
pascal@25458 513 %if CHSupTo8GB != 0 || CHSupTo32MB != 0
pascal@25458 514 shr ax, 2
pascal@25458 515 or cl, al
pascal@25449 516 ; cl = MSB 8...9 of cylinder no. + sector no.
pascal@25458 517 %endif
pascal@25449 518 mov dh, dl
pascal@25449 519 ; dh = head no.
pascal@25449 520 mov dl, [bx(DriveNumber)] ; restore BIOS boot drive number
pascal@25449 521 %endif
pascal@25449 522
pascal@25454 523 ReadSectorRetry:
pascal@24525 524 mov si, sp
pascal@24478 525 mov ah, 42h ; ah = 42h = extended read function no.
pascal@24478 526 int 13h ; extended read sectors (DL, DS:SI)
pascal@24478 527 jnc ReadSuccess ; CF = 0 if no error
pascal@24476 528
pascal@25449 529 %if CHSsupport != 0
pascal@25449 530 mov ax, 201h ; al = sector count = 1
pascal@25449 531 ; ah = 2 = read function no.
pascal@25449 532 int 13h ; read sectors (AL, CX, DX, ES:BX)
pascal@25449 533
pascal@25449 534 jnc ReadSuccess ; CF = 0 if no error
pascal@25449 535 %endif
pascal@25449 536 %if ReadRetry != 0
pascal@25458 537 %if CHSsupport != 0
pascal@25449 538 cbw ; ah = 0 = reset function
pascal@25458 539 %else
pascal@24945 540 xor ax, ax ; ah = 0 = reset function
pascal@25458 541 %endif
pascal@24476 542 int 13h ; reset drive (DL)
pascal@24476 543
pascal@25457 544 dec bp ; up to 32 retries
pascal@25454 545 jnz ReadSectorRetry
pascal@25449 546 %endif
pascal@24525 547
pascal@24476 548 call Error
pascal@24476 549 db "Read error."
pascal@24476 550
pascal@24478 551 ReadSuccess:
pascal@24476 552
pascal@24476 553 popa ; sp += 16
pascal@24478 554 popa
pascal@24476 555 ret
pascal@24476 556
pascal@24942 557 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24942 558 ;; Fill free space with zeroes ;;
pascal@24942 559 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24942 560
pascal@25458 561 times (512-13-($-$$)) db 0
pascal@24476 562
pascal@24476 563 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 564 ;; Name of the file to load and run ;;
pascal@24476 565 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 566
pascal@25463 567 NameLength equ 11
pascal@25463 568 ProgramName times NameLength db 0 ; name and extension
pascal@24476 569
pascal@24476 570 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 571 ;; End of the sector ID ;;
pascal@24476 572 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 573
pascal@24476 574 dw 0AA55h ; BIOS checks for this ID