wok annotate BootProg/stuff/boot16.asm @ rev 25458

Update some web_site
author Pascal Bellard <pascal.bellard@slitaz.org>
date Tue Sep 27 16:21:52 2022 +0000 (21 months ago)
parents ad0bc3efbf37
children 81fc994927a6
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 boot16.asm -f bin -o boot16.bin ;;
pascal@24476 10 ;; ;;
pascal@24476 11 ;; ;;
pascal@24476 12 ;; Features: ;;
pascal@24476 13 ;; ~~~~~~~~~ ;;
pascal@24476 14 ;; - FAT12 and FAT16 supported using BIOS int 13h function 42h or 02h. ;;
pascal@24476 15 ;; ;;
pascal@24476 16 ;; - Loads a 16-bit executable file in the MS-DOS .COM or .EXE format ;;
pascal@24476 17 ;; from the root directory of a disk and transfers control to it ;;
pascal@24476 18 ;; (the "ProgramName" variable holds the name of the file to be loaded) ;;
pascal@24476 19 ;; Its maximum size can be up to 635KB without Extended BIOS Data area. ;;
pascal@24476 20 ;; ;;
pascal@24476 21 ;; - Prints an error if the file isn't found or couldn't be read ;;
pascal@24476 22 ;; ("File not found" or "Read error") ;;
pascal@24476 23 ;; and waits for a key to be pressed, then executes the Int 19h ;;
pascal@24476 24 ;; instruction and lets the BIOS continue bootstrap. ;;
pascal@24476 25 ;; ;;
pascal@24476 26 ;; - cpu 8086 is supported ;;
pascal@24476 27 ;; ;;
pascal@24476 28 ;; ;;
pascal@24476 29 ;; Known Bugs: ;;
pascal@24476 30 ;; ~~~~~~~~~~~ ;;
pascal@24476 31 ;; - All bugs are fixed as far as I know. The boot sector has been tested ;;
pascal@24476 32 ;; on the following types of diskettes (FAT12): ;;
pascal@24476 33 ;; - 360KB 5"25 ;;
pascal@24476 34 ;; - 1.2MB 5"25 ;;
pascal@24476 35 ;; - 1.44MB 3"5 ;;
pascal@24476 36 ;; on my HDD (FAT16). ;;
pascal@24476 37 ;; ;;
pascal@24476 38 ;; ;;
pascal@24476 39 ;; Memory Layout: ;;
pascal@24476 40 ;; ~~~~~~~~~~~~~~ ;;
pascal@24476 41 ;; The diagram below shows the typical memory layout. The actual location ;;
pascal@24476 42 ;; of the boot sector and its stack may be lower than A0000H if the BIOS ;;
pascal@24476 43 ;; reserves memory for its Extended BIOS Data Area just below A0000H and ;;
pascal@24476 44 ;; reports less than 640 KB of RAM via its Int 12H function. ;;
pascal@24476 45 ;; ;;
pascal@24476 46 ;; physical address ;;
pascal@24476 47 ;; +------------------------+ 00000H ;;
pascal@24476 48 ;; | Interrupt Vector Table | ;;
pascal@24476 49 ;; +------------------------+ 00400H ;;
pascal@24476 50 ;; | BIOS Data Area | ;;
pascal@24476 51 ;; +------------------------+ 00500H ;;
pascal@24476 52 ;; | PrtScr Status / Unused | ;;
pascal@24476 53 ;; +------------------------+ 00600H ;;
pascal@24476 54 ;; | Loaded Image | ;;
pascal@24476 55 ;; +------------------------+ nnnnnH ;;
pascal@24476 56 ;; | Available Memory | ;;
pascal@24476 57 ;; +------------------------+ A0000H - 512 - 3KB ;;
pascal@24476 58 ;; | Boot Sector | ;;
pascal@24476 59 ;; +------------------------+ A0000H - 3KB ;;
pascal@24476 60 ;; | 3KB Boot Stack | ;;
pascal@24476 61 ;; +------------------------+ A0000H ;;
pascal@24476 62 ;; | Video RAM | ;;
pascal@24476 63 ;; ;;
pascal@24476 64 ;; ;;
pascal@24476 65 ;; Boot Image Startup (register values): ;;
pascal@24476 66 ;; ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ;;
pascal@24945 67 ;; ax = 0ffffh (both FCB in the PSP don't have a valid drive identifier), ;;
pascal@25454 68 ;; bx = 0, dl = BIOS boot drive number (e.g. 0, 80H) ;;
pascal@24476 69 ;; cs:ip = program entry point ;;
pascal@24476 70 ;; ss:sp = program stack (don't confuse with boot sector's stack) ;;
pascal@24476 71 ;; COM program defaults: cs = ds = es = ss = 50h, sp = 0, ip = 100h ;;
pascal@24476 72 ;; EXE program defaults: ds = es = EXE data - 10h (fake MS-DOS psp), ;;
pascal@24476 73 ;; cs:ip and ss:sp depends on EXE header ;;
pascal@24476 74 ;; Magic numbers: ;;
pascal@24476 75 ;; si = 16381 (prime number 2**14-3) ;;
pascal@24476 76 ;; di = 32749 (prime number 2**15-19) ;;
pascal@24476 77 ;; bp = 65521 (prime number 2**16-15) ;;
pascal@24476 78 ;; The magic numbers let the program know whether it has been loaded by ;;
pascal@24476 79 ;; this boot sector or by MS-DOS, which may be handy for universal, bare- ;;
pascal@24476 80 ;; metal and MS-DOS programs. ;;
pascal@24945 81 ;; The command line contains no arguments. ;;
pascal@24476 82 ;; ;;
pascal@24476 83 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 84
pascal@24476 85 %define bx(label) bx+label-boot
pascal@25450 86 %define si(label) si+label-boot
pascal@25458 87 NullEntryCheck equ 1 ; +2 bytes
pascal@25450 88 ReadRetry equ 1 ; +9 bytes
pascal@25450 89 LBAsupport equ 1 ; +16 bytes
pascal@25450 90 Over2GB equ 1 ; +5 bytes
pascal@25450 91 GeometryCheck equ 1 ; +18 bytes
pascal@25458 92 SectorOf512Bytes equ 1 ; -4/-6 bytes
pascal@24476 93
pascal@24476 94 [BITS 16]
pascal@24476 95 [CPU 8086]
pascal@24476 96
pascal@24476 97 ImageLoadSeg equ 60h
pascal@24476 98 StackSize equ 3072 ; Stack + cluster list
pascal@24476 99
pascal@24476 100 [SECTION .text]
pascal@24476 101 [ORG 0]
pascal@24476 102
pascal@24476 103 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 104 ;; Boot sector starts here ;;
pascal@24476 105 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 106
pascal@24476 107 boot:
pascal@25450 108 DriveNumber:
pascal@24476 109 jmp short start ; MS-DOS/Windows checks for this jump
pascal@24476 110 nop
pascal@24476 111 bsOemName DB "BootProg" ; 0x03
pascal@24476 112
pascal@24476 113 ;;;;;;;;;;;;;;;;;;;;;
pascal@24476 114 ;; BPB starts here ;;
pascal@24476 115 ;;;;;;;;;;;;;;;;;;;;;
pascal@24476 116
pascal@24479 117 bpbBytesPerSector DW 0 ; 0x0B
pascal@24479 118 bpbSectorsPerCluster DB 0 ; 0x0D
pascal@24479 119 bpbReservedSectors DW 0 ; 0x0E
pascal@24479 120 bpbNumberOfFATs DB 0 ; 0x10
pascal@24479 121 bpbRootEntries DW 0 ; 0x11
pascal@24479 122 bpbTotalSectors DW 0 ; 0x13
pascal@24479 123 bpbMedia DB 0 ; 0x15
pascal@24479 124 bpbSectorsPerFAT DW 0 ; 0x16
pascal@24479 125 bpbSectorsPerTrack DW 0 ; 0x18
pascal@24479 126 bpbHeadsPerCylinder DW 0 ; 0x1A
pascal@24479 127 bpbHiddenSectors DD 0 ; 0x1C
pascal@24479 128 bpbTotalSectorsBig DD 0 ; 0x20
pascal@24476 129
pascal@24476 130 ;;;;;;;;;;;;;;;;;;;
pascal@24476 131 ;; BPB ends here ;;
pascal@24476 132 ;;;;;;;;;;;;;;;;;;;
pascal@24476 133
pascal@24479 134 bsDriveNumber DB 0 ; 0x24
pascal@24479 135 bsUnused DB 0 ; 0x25
pascal@24479 136 bsExtBootSignature DB 0 ; 0x26
pascal@24479 137 bsSerialNumber DD 0 ; 0x27
pascal@25458 138 bsVolumeLabel times 11 DB " " ; 0x2B "NO NAME "
pascal@25458 139 bsFileSystem times 8 DB " " ; 0x36 "FAT12 " or "FAT16 "
pascal@24476 140
pascal@24476 141 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 142 ;; Boot sector code starts here ;;
pascal@24476 143 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 144
pascal@24476 145 start:
pascal@24476 146 cld
pascal@24476 147
pascal@24476 148 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 149 ;; How much RAM is there? ;;
pascal@24476 150 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 151
pascal@24476 152 int 12h ; get conventional memory size (in KBs)
pascal@24476 153 mov cx, 106h
pascal@24476 154 shl ax, cl ; and convert it to 16-byte paragraphs
pascal@24476 155
pascal@24476 156 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 157 ;; Reserve memory for the boot sector and its stack ;;
pascal@24476 158 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 159
pascal@24476 160 sub ax, (512+StackSize) /16 ; reserve bytes for the code and the stack
pascal@24476 161 mov es, ax ; cs:0 = ds:0 = ss:0 -> top - 512 - StackSize
pascal@24476 162 mov ss, ax
pascal@24476 163 mov sp, 512+StackSize ; bytes 0-511 are reserved for the boot code
pascal@24476 164
pascal@24476 165 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 166 ;; Copy ourselves to top of memory ;;
pascal@24476 167 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 168
pascal@24476 169 mov si, 7C00h
pascal@24476 170 xor di, di
pascal@24476 171 mov ds, di
pascal@25450 172 push es
pascal@25450 173 mov [si(DriveNumber)], dx ; store BIOS boot drive number
pascal@24476 174 rep movsw ; move 512 bytes (+ 12)
pascal@24476 175
pascal@24476 176 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 177 ;; Jump to the copy ;;
pascal@24476 178 ;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 179
pascal@24476 180 mov cl, byte main
pascal@24476 181 push cx
pascal@24476 182 retf
pascal@24476 183
pascal@24476 184 main:
pascal@24476 185 %if ImageLoadSeg != main-boot
pascal@24476 186 %if ImageLoadSeg >= 100h
pascal@24476 187 mov cx, ImageLoadSeg
pascal@24476 188 %else
pascal@24476 189 mov cl, ImageLoadSeg
pascal@24476 190 %endif
pascal@24476 191 %endif
pascal@24476 192 push cx
pascal@24476 193
pascal@24476 194 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 195 ;; Get drive parameters ;;
pascal@24476 196 ;; Update heads count ;;
pascal@24476 197 ;; for current BIOS ;;
pascal@24476 198 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 199
pascal@25450 200 %if GeometryCheck != 0
pascal@24476 201 mov ah, 8
pascal@24476 202 int 13h ; may destroy SI,BP, and DS registers
pascal@25450 203 %endif
pascal@24476 204 ; update AX,BL,CX,DX,DI, and ES registers
pascal@24476 205 push cs
pascal@24476 206 pop ds
pascal@24476 207 xor bx, bx
pascal@24476 208
pascal@25450 209 %if GeometryCheck != 0
pascal@24479 210 and cx, byte 3Fh
pascal@24476 211 cmp [bx(bpbSectorsPerTrack)], cx
pascal@24476 212 jne BadParams ; verify updated and validity
pascal@24476 213 mov al, dh
pascal@24476 214 inc ax
pascal@24476 215 mov [bpbHeadsPerCylinder], ax
pascal@24476 216 BadParams:
pascal@25450 217 %endif
pascal@24476 218
pascal@24476 219 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 220 ;; Load FAT (FAT12: 6KB max, FAT16: 128KB max) ;;
pascal@24476 221 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 222
pascal@24476 223 pop es ; ImageLoadSeg
pascal@24476 224 push es
pascal@24476 225
pascal@24476 226 mul bx ; dx:ax = 0 = LBA (LBA are relative to FAT)
pascal@25458 227 mov di, word [bx(bpbSectorsPerFAT)]
pascal@24476 228
pascal@25458 229 call ReadDISectors ; read fat; clear ax, cx, di; bp = SectorsPerFAT
pascal@24476 230
pascal@24476 231 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 232 ;; load the root directory in ;;
pascal@24476 233 ;; its entirety (16KB max) ;;
pascal@24476 234 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 235
pascal@25458 236 %if SectorOf512Bytes != 0
pascal@25458 237 mov di, word [bx(bpbRootEntries)]
pascal@25458 238 mov cl, 4
pascal@25458 239 shr di, cl ; di = root directory size in sectors
pascal@25458 240 %else
pascal@24942 241 mov al, 32
pascal@24476 242
pascal@24476 243 mul word [bx(bpbRootEntries)]
pascal@24476 244 div word [bx(bpbBytesPerSector)]
pascal@25458 245 xchg ax, di ; di = root directory size in sectors, clear ah
pascal@25458 246 %endif
pascal@24476 247
pascal@24476 248 mov al, [bpbNumberOfFATs]
pascal@25458 249 mul bp ; [bx(bpbSectorsPerFAT)], set by ReadDISectors
pascal@24476 250
pascal@25457 251 push es ; read root directory
pascal@25458 252 call ReadDISectors ; clear ax, cx, di; bp = first data sector
pascal@24476 253 pop es
pascal@24476 254
pascal@24476 255 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 256 ;; Look for the COM/EXE file to load and run ;;
pascal@24476 257 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 258
pascal@24476 259 ; es:di -> root entries array
pascal@24476 260
pascal@24476 261 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 262 ;; Looks for the file/dir ProgramName ;;
pascal@24476 263 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 264 ;; Input: ES:DI -> root directory array ;;
pascal@24476 265 ;; Output: SI = cluster number ;;
pascal@24476 266 ;; AX = file sector count ;;
pascal@24476 267 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 268
pascal@24476 269 FindNameCycle:
pascal@24476 270 push di
pascal@25454 271 mov cl, NameLength
pascal@24476 272 mov si, ProgramName ; ds:si -> program name
pascal@24476 273 repe cmpsb
pascal@24476 274 pop di
pascal@24476 275 je FindNameFound
pascal@25450 276 %if NullEntryCheck != 0
pascal@25458 277 scasb ; Z == NC
pascal@25458 278 cmc
pascal@25458 279 lea di, [di+31]
pascal@25458 280 dec word [bx(bpbRootEntries)]
pascal@25458 281 ja FindNameCycle ; next root entry
pascal@25450 282 %else
pascal@25450 283 add di, byte 32
pascal@24476 284 dec word [bx(bpbRootEntries)]
pascal@24476 285 jnz FindNameCycle ; next root entry
pascal@25458 286 %endif
pascal@24476 287
pascal@24476 288 FindNameFailed:
pascal@24476 289 call Error
pascal@24476 290 db "File not found."
pascal@24476 291
pascal@24476 292 FindNameFound:
pascal@24476 293 push si
pascal@24476 294 mov si, [es:di+1Ah] ; si = cluster no.
pascal@24476 295 les ax, [es:di+1Ch] ; file size
pascal@24476 296 mov dx, es
pascal@24476 297 div word [bx(bpbBytesPerSector)]
pascal@24476 298 cmp bx, dx ; sector aligned ?
pascal@24476 299 adc ax, bx ; file last sector
pascal@24476 300 pop di ; di = ClusterList
pascal@24476 301
pascal@24476 302 pop es ; ImageLoadSeg
pascal@24476 303 push ax
pascal@24476 304
pascal@24476 305 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 306 ;; build cluster list ;;
pascal@24476 307 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 308 ;; Input: ES:0 -> FAT ;;
pascal@24476 309 ;; SI = first cluster ;;
pascal@24476 310 ;; DI = cluster list :;
pascal@24476 311 ;; CH = 0 ;;
pascal@24476 312 ;; Output: SI = cluster list ;;
pascal@24476 313 ;; CH = 0 ;;
pascal@24476 314 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 315
pascal@25458 316 FAT12 equ 1
pascal@25458 317 FAT16 equ 1
pascal@25458 318 TINYFAT16 equ 1
pascal@25453 319 push di ; up to 2 * 635K / BytesPerCluster = 2540 bytes
pascal@25450 320 %if FAT12 == 1
pascal@25454 321 mov cl, 12
pascal@25450 322 %endif
pascal@24476 323 ClusterLoop:
pascal@24476 324 mov [di], si
pascal@25450 325 add si, si ; si = cluster * 2
pascal@25450 326 %if FAT16 == 1
pascal@24476 327 mov ax, es ; ax = FAT segment = ImageLoadSeg
pascal@25094 328 jnc First64k
pascal@24476 329 mov ah, (1000h+ImageLoadSeg)>>8 ; adjust segment for 2nd part of FAT16
pascal@25094 330 First64k:
pascal@25453 331 %if FAT12 == 1
pascal@25457 332 mov dx, 0FFF6h
pascal@25454 333 %if TINYFAT16 == 1
pascal@25453 334 test [bx(bsFileSystem+4)], cl ; FAT12 or FAT16 ? clear C
pascal@25458 335 jne ReadClusterFat16
pascal@25454 336 %else
pascal@25454 337 cmp [bx(bpbSectorsPerFAT)], cx ; 1..12 = FAT12, 16..256 = FAT16
pascal@25458 338 ja ReadClusterFat16
pascal@25454 339 %endif
pascal@24942 340 mov dh, 0Fh
pascal@25453 341 %endif
pascal@25450 342 %endif
pascal@25450 343 %if FAT12 == 1
pascal@25087 344 add si, [di]
pascal@24476 345 shr si, 1 ; si = cluster * 3 / 2
pascal@25450 346 %endif
pascal@25450 347 %if FAT16 == 1
pascal@24942 348 ReadClusterFat16:
pascal@25094 349 push ds
pascal@25087 350 mov ds, ax
pascal@24476 351 lodsw ; ax = next cluster
pascal@25094 352 pop ds
pascal@25450 353 %else
pascal@25453 354 es lodsw
pascal@25450 355 %endif
pascal@25450 356 %if FAT12 == 1
pascal@24476 357 jnc ReadClusterEven
pascal@25454 358 rol ax, cl
pascal@24476 359 ReadClusterEven:
pascal@25094 360 scasw ; di += 2
pascal@25454 361 %if FAT16 == 1
pascal@24942 362 and ah, dh ; mask cluster value
pascal@24942 363 cmp ax, dx
pascal@25454 364 %else
pascal@25453 365 and ah, 0Fh ; mask cluster value
pascal@25457 366 cmp ax, 0FF6h
pascal@25454 367 %endif
pascal@25454 368 %else
pascal@25454 369 scasw ; di += 2
pascal@25457 370 cmp ax, 0FFF6h
pascal@25453 371 %endif
pascal@24476 372 xchg ax, si
pascal@24476 373 jc ClusterLoop
pascal@24476 374 pop si
pascal@24476 375 pop di ; file size in sectors
pascal@24476 376
pascal@24476 377 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 378 ;; Load the entire file ;;
pascal@24476 379 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 380 ;; Input: ES:0 -> buffer ;;
pascal@24476 381 ;; SI = cluster list ;;
pascal@24476 382 ;; DI = file sectors ;;
pascal@24476 383 ;; CH = 0 ;;
pascal@24945 384 ;; BP = 1st data sec ;;
pascal@24476 385 ;; Output: BP:0 -> buffer ;;
pascal@24476 386 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 387
pascal@24476 388 push es
pascal@24476 389
pascal@24476 390 ReadClusters:
pascal@24476 391 lodsw
pascal@24476 392 dec ax
pascal@24476 393 dec ax
pascal@24476 394
pascal@25454 395 mov cl, [bx(bpbSectorsPerCluster)] ; 1..128
pascal@24476 396 mul cx ; cx = sector count (ch = 0)
pascal@24476 397
pascal@24476 398 add ax, bp ; LBA for cluster data
pascal@24476 399 adc dx, bx ; dx:ax = LBA
pascal@24476 400
pascal@25458 401 call ReadSectors ; clear ax, restore dx
pascal@24476 402
pascal@25458 403 jne ReadClusters ; until end of file
pascal@24476 404
pascal@24476 405 pop bp ; ImageLoadSeg
pascal@24476 406
pascal@24476 407 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 408 ;; Type detection, .COM or .EXE? ;;
pascal@24476 409 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 410
pascal@24476 411 mov ds, bp ; bp=ds=seg the file is loaded to
pascal@24476 412
pascal@24476 413 add bp, [bx+08h] ; bp = image base
pascal@24476 414 mov di, [bx+18h] ; di = reloc table pointer
pascal@24476 415
pascal@24476 416 cmp word [bx], 5A4Dh ; "MZ" signature?
pascal@24476 417 je RelocateEXE ; yes, it's an EXE program
pascal@24476 418
pascal@24476 419 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 420 ;; Setup and run a .COM program ;;
pascal@24476 421 ;; Set CS=DS=ES=SS SP=0 IP=100h ;;
pascal@25454 422 ;; AX=0ffffh BX=0 DX=drive and ;;
pascal@25454 423 ;; cmdline=void ;;
pascal@24476 424 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 425
pascal@24942 426 mov di, 100h ; ip
pascal@24476 427 mov bp, ImageLoadSeg-10h ; "org 100h" stuff :)
pascal@24476 428 mov ss, bp
pascal@24476 429 xor sp, sp
pascal@24476 430 push bp ; cs, ds and es
pascal@24476 431 jmp short Run
pascal@24476 432
pascal@24476 433 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 434 ;; Relocate, setup and run a .EXE program ;;
pascal@24476 435 ;; Set CS:IP, SS:SP, DS, ES and AX according ;;
pascal@24476 436 ;; to wiki.osdev.org/MZ#Initial_Program_State ;;
pascal@25454 437 ;; AX=0ffffh BX=0 DX=drive cmdline=void ;;
pascal@24476 438 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 439
pascal@24476 440 ReloCycle:
pascal@24476 441 add [di+2], bp ; item seg (abs)
pascal@24476 442 les si, [di] ; si = item ofs, es = item seg
pascal@24476 443 add [es:si], bp ; fixup
pascal@24476 444 scasw ; di += 2
pascal@24476 445 scasw ; point to next entry
pascal@24476 446
pascal@24476 447 RelocateEXE:
pascal@24942 448 dec word [bx+06h] ; reloc items, 32768 max (128KB table)
pascal@24942 449 jns ReloCycle
pascal@24476 450 ; PSP don't have a valid drive identifier
pascal@24476 451 les si, [bx+0Eh]
pascal@24476 452 add si, bp
pascal@24476 453 mov ss, si ; ss for EXE
pascal@24476 454 mov sp, es ; sp for EXE
pascal@24476 455
pascal@24476 456 lea si, [bp-10h] ; ds and es both point to the segment
pascal@24476 457 push si ; containing the PSP structure
pascal@24476 458
pascal@24476 459 add bp, [bx+16h] ; cs for EXE
pascal@24942 460 mov di, [bx+14h] ; ip for EXE
pascal@24476 461 Run:
pascal@24476 462 pop ds
pascal@24476 463 push bp
pascal@24942 464 push di
pascal@24476 465 push ds
pascal@24476 466 pop es
pascal@24942 467 mov [80h], ax ; clear cmdline
pascal@24942 468 dec ax ; both FCB in the PSP don't have a valid drive identifier
pascal@24476 469
pascal@24476 470 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 471 ;; Set the magic numbers so the program knows that it ;;
pascal@24476 472 ;; has been loaded by this bootsector and not by MS-DOS ;;
pascal@24476 473 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 474 mov si, 16381 ; prime number 2**14-3
pascal@24476 475 mov di, 32749 ; prime number 2**15-19
pascal@24476 476 mov bp, 65521 ; prime number 2**16-15
pascal@24476 477
pascal@24476 478 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 479 ;; All done, transfer control to the program now ;;
pascal@24476 480 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 481 retf
pascal@24476 482
pascal@25458 483 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@25458 484 ;; Error Messaging Code ;;
pascal@25458 485 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@25458 486
pascal@25458 487 Error:
pascal@25458 488 pop si
pascal@25458 489
pascal@25458 490 PutStr:
pascal@25458 491 mov ah, 0Eh
pascal@25458 492 mov bl, 7
pascal@25458 493 lodsb
pascal@25458 494 int 10h
pascal@25458 495 cmp al, "."
pascal@25458 496 jne PutStr
pascal@25458 497
pascal@25458 498 cbw
pascal@25458 499 int 16h ; wait for a key...
pascal@25458 500 int 19h ; bootstrap
pascal@25458 501
pascal@25458 502 Stop:
pascal@25458 503 hlt
pascal@25458 504 jmp short Stop
pascal@25458 505
pascal@25458 506 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@25458 507 ;; Read sectors using BIOS Int 13h ;;
pascal@25458 508 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@25458 509 ;; Input: DX:AX = LBA relative to FAT ;;
pascal@25458 510 ;; BX = 0 ;;
pascal@25458 511 ;; DI = sector count ;;
pascal@25458 512 ;; ES:BX -> buffer address ;;
pascal@25458 513 ;; Output: ES:BX -> next address ;;
pascal@25458 514 ;; BX = 0 ;;
pascal@25458 515 ;; CX = 0 ;;
pascal@25458 516 ;; DI = 0 ;;
pascal@25458 517 ;; DL = drive number ;;
pascal@25458 518 ;; DX:BP = next LBA from FAT ;;
pascal@25458 519 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@25458 520
pascal@25458 521 ReadDISectors:
pascal@25458 522 mov bp, di
pascal@24476 523 add bp, ax ; adjust LBA for cluster data
pascal@24476 524
pascal@25458 525 mov cx, di ; no cluster size limit
pascal@24476 526
pascal@24476 527 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@25458 528 ;; Read sectors using BIOS Int 13h ;;
pascal@24476 529 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 530 ;; Input: DX:AX = LBA relative to FAT ;;
pascal@24476 531 ;; BX = 0 ;;
pascal@24476 532 ;; CX = sector count ;;
pascal@24476 533 ;; DI = file sectors ;;
pascal@24476 534 ;; ES:BX -> buffer address ;;
pascal@24476 535 ;; Output: ES:BX -> next address ;;
pascal@24476 536 ;; BX = 0 ;;
pascal@24476 537 ;; CX or DI = 0 ;;
pascal@24476 538 ;; DL = drive number ;;
pascal@24476 539 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 540
pascal@25458 541 ReadSectors:
pascal@24476 542 add ax, [bx(bpbHiddenSectors)]
pascal@24476 543 adc dx, [bx(bpbHiddenSectors)+2]
pascal@24476 544 add ax, [bx(bpbReservedSectors)]
pascal@24476 545
pascal@24476 546 push si
pascal@24476 547 ReadSectorNext:
pascal@24476 548 adc dx, bx
pascal@24476 549 push di
pascal@24476 550 push cx
pascal@24476 551
pascal@25450 552 %if LBAsupport != 0
pascal@24476 553 push bx
pascal@24476 554 push bx
pascal@25450 555 %endif
pascal@24476 556 push dx ; 32-bit LBA: up to 2TB
pascal@24476 557 push ax
pascal@24476 558 push es
pascal@25450 559 %if ReadRetry != 0 || LBAsupport != 0
pascal@25450 560 mov di, 16 ; packet size byte = 16, reserved byte = 0
pascal@25450 561 %endif
pascal@25450 562 %if LBAsupport != 0
pascal@24476 563 push bx
pascal@24476 564 inc bx ; sector count word = 1
pascal@24476 565 push bx
pascal@24476 566 dec bx
pascal@24476 567 push di
pascal@25450 568 %endif
pascal@24476 569
pascal@25450 570 %if Over2GB != 0
pascal@24476 571 xchg ax, cx ; save low LBA
pascal@24476 572 xchg ax, dx ; get high LBA
pascal@25452 573 cwd ; clear dx (LBA offset <1TB)
pascal@25450 574 idiv word [bx(bpbSectorsPerTrack)] ; up to 8GB disks
pascal@24476 575
pascal@24476 576 xchg ax, cx ; restore low LBA, save high LBA / SPT
pascal@25450 577 %else
pascal@25450 578 xor cx, cx ; up to 2GB disks otherwise divide error interrupt !
pascal@25450 579 %endif
pascal@25450 580 idiv word [bx(bpbSectorsPerTrack)]
pascal@24476 581 ; ax = LBA / SPT
pascal@24476 582 ; dx = LBA % SPT = sector - 1
pascal@24476 583 inc dx
pascal@24476 584
pascal@24476 585 xchg cx, dx ; restore high LBA / SPT, save sector no.
pascal@25450 586 idiv word [bx(bpbHeadsPerCylinder)]
pascal@24476 587 ; ax = (LBA / SPT) / HPC = cylinder
pascal@24476 588 ; dx = (LBA / SPT) % HPC = head
pascal@25458 589
pascal@25458 590 xchg ch, al ; clear al
pascal@24476 591 ; ch = LSB 0...7 of cylinder no.
pascal@25458 592 shr ax, 1
pascal@25458 593 shr ax, 1
pascal@24476 594 or cl, al
pascal@24476 595 ; cl = MSB 8...9 of cylinder no. + sector no.
pascal@24476 596 mov dh, dl
pascal@24476 597 ; dh = head no.
pascal@24476 598
pascal@24476 599 ReadSectorRetry:
pascal@25450 600 mov dl, [bx(DriveNumber)]
pascal@24476 601 ; dl = drive no.
pascal@25450 602 mov si, sp
pascal@25450 603 %if LBAsupport != 0
pascal@24476 604 mov ah, 42h ; ah = 42h = extended read function no.
pascal@24476 605 int 13h ; extended read sectors (DL, DS:SI)
pascal@24476 606 jnc ReadSectorNextSegment
pascal@25450 607 %endif
pascal@24476 608
pascal@24476 609 mov ax, 201h ; al = sector count = 1
pascal@24476 610 ; ah = 2 = read function no.
pascal@24476 611 int 13h ; read sectors (AL, CX, DX, ES:BX)
pascal@24476 612
pascal@24476 613 jnc ReadSectorNextSegment
pascal@25450 614 %if ReadRetry != 0
pascal@24476 615 cbw ; ah = 0 = reset function
pascal@24476 616 int 13h ; reset drive (DL)
pascal@24476 617
pascal@24476 618 dec di
pascal@25457 619 jnz ReadSectorRetry ; up to 15 extra attempt
pascal@25450 620 %endif
pascal@24476 621
pascal@24476 622 call Error
pascal@24476 623 db "Read error."
pascal@24476 624
pascal@24476 625 ReadSectorNextSegment:
pascal@24476 626
pascal@25450 627 %if LBAsupport != 0
pascal@24476 628 pop ax ; al = 16
pascal@25458 629 %if SectorOf512Bytes != 0
pascal@25458 630 add word [si+6], byte 32 ; adjust segment for next sector
pascal@25458 631 %else
pascal@24476 632 mul byte [bx(bpbBytesPerSector)+1] ; = (bpbBytesPerSector/256)*16
pascal@25458 633 add [si+6], ax ; adjust segment for next sector
pascal@25458 634 %endif
pascal@24476 635 pop cx ; sector count = 1
pascal@24476 636 pop bx
pascal@25450 637 %else
pascal@25458 638 %if SectorOf512Bytes != 0
pascal@25458 639 add word [si], byte 32 ; adjust segment for next sector
pascal@25458 640 %else
pascal@25450 641 mov al, 16
pascal@25450 642 mul byte [bx(bpbBytesPerSector)+1] ; = (bpbBytesPerSector/256)*16
pascal@25450 643 add [si], ax ; adjust segment for next sector
pascal@25458 644 %endif
pascal@25450 645 %endif
pascal@24476 646 pop es ; es:0 updated
pascal@24476 647 pop ax
pascal@24476 648 pop dx
pascal@25450 649 %if LBAsupport != 0
pascal@24476 650 pop di
pascal@24476 651 pop di
pascal@24476 652 add ax, cx ; adjust LBA for next sector
pascal@25450 653 %else
pascal@25450 654 add ax, 1 ; adjust LBA for next sector
pascal@25450 655 %endif
pascal@24476 656
pascal@24476 657 pop cx ; cluster sectors to read
pascal@24476 658 pop di ; file sectors to read
pascal@24476 659 dec di ; keep C
pascal@25457 660 loopne ReadSectorNext ; until cluster sector count or file sector count
pascal@24476 661 pop si
pascal@24942 662 mov ax, bx ; clear ax
pascal@25450 663 mov dx, [bx(DriveNumber)] ; pass the BIOS boot drive to Run or Error
pascal@24476 664
pascal@24476 665 ret
pascal@24476 666
pascal@24942 667 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24942 668 ;; Fill free space with zeroes ;;
pascal@24942 669 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24942 670
pascal@25458 671 times (512-13-($-$$)) db 0
pascal@24476 672
pascal@24476 673 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 674 ;; Name of the file to load and run ;;
pascal@24476 675 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 676
pascal@24476 677 ProgramName db "STARTUP BIN" ; name and extension each must be
pascal@25450 678 times (510-($-$$)) db ' ' ; padded with spaces (11 bytes total)
pascal@25454 679 NameLength equ $-ProgramName
pascal@24476 680
pascal@24476 681 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 682 ;; End of the sector ID ;;
pascal@24476 683 ;;;;;;;;;;;;;;;;;;;;;;;;;;
pascal@24476 684
pascal@24476 685 ClusterList dw 0AA55h ; BIOS checks for this ID