boot0.S revision 185776
1/* 2 * Copyright (c) 2008 Luigi Rizzo (mostly documentation) 3 * Copyright (c) 2002 Bruce M. Simpson 4 * Copyright (c) 1998 Robert Nordier 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms are freely 8 * permitted provided that the above copyright notice and this 9 * paragraph and the following disclaimer are duplicated in all 10 * such forms. 11 * 12 * This software is provided "AS IS" and without any express or 13 * implied warranties, including, without limitation, the implied 14 * warranties of merchantability and fitness for a particular 15 * purpose. 16 * 17 * $FreeBSD: head/sys/boot/i386/boot0/boot0.S 185776 2008-12-08 20:53:27Z sobomax $ 18 */ 19 20/* build options: */ 21#ifdef SIO /* use serial console on COM1. */ 22#endif 23 24#ifdef PXE /* enable PXE/INT18 booting with F6 */ 25#endif 26 27#ifdef CHECK_DRIVE /* make sure we boot from a HD. */ 28#endif 29 30#ifdef ONLY_F_KEYS /* Only F1..F6, no digits on console */ 31#endif 32 33#ifdef VOLUME_SERIAL /* support Volume serial number */ 34#define B0_BASE 0x1ae /* move the internal data area */ 35#define SAVE_MEMORY 36#else 37#define B0_BASE 0x1b2 38#endif 39 40#ifdef TEST /* enable some test code */ 41#define SAVE_MEMORY 42#define SAVE_MORE_MEMORY 43#endif 44 45/* 46 * Note - this code uses many tricks to save space and fit in one sector. 47 * This includes using side effects of certain instructions, reusing 48 * register values from previous operations, etc. 49 * Be extremely careful when changing the code, even for simple things. 50 */ 51 52/* 53 * BOOT BLOCK STRUCTURE 54 * 55 * This code implements a Master Boot Record (MBR) for an Intel/PC disk. 56 * It is 512 bytes long and it is normally loaded by the BIOS (or another 57 * bootloader) at 0:0x7c00. This code depends on %cs:%ip being 0:0x7c00 58 * 59 * The initial chunk of instructions is used as a signature by external 60 * tools (e.g. boot0cfg) which can manipulate the block itself. 61 * 62 * The area at offset 0x1b2 contains a magic string ('Drive '), also 63 * used as a signature to detect the block, and some variables that can 64 * be updated by boot0cfg (and optionally written back to the disk). 65 * These variables control the operation of the bootloader itself, 66 * e.g. which partitions to enable, the timeout, the use of LBA 67 * (called 'packet') or CHS mode, whether to force a drive number, 68 * and whether to write back the user's selection back to disk. 69 * 70 * As in every Master Boot Record, the partition table is at 0x1be, 71 * made of four 16-byte entries each containing: 72 * 73 * OFF SIZE DESCRIPTION 74 * 0 1 status (0x80: bootable, 0: non bootable) 75 * 1 3 start sector CHS 76 * 8:head, 6:sector, 2:cyl bit 9..8, 8:cyl bit 7..0 77 * 4 1 partition type 78 * 5 3 end sector CHS 79 * 8 4 LBA of first sector 80 * 12 4 partition size in sectors 81 * 82 * and followed by the two bytes 0x55, 0xAA (MBR signature). 83 */ 84 85 86/* 87 * BOOT BLOCK OPERATION 88 * 89 * On entry, the registers contain the following values: 90 * 91 * %cs:%ip 0:0x7c00 92 * %dl drive number (0x80, 0x81, ... ) 93 * %si pointer to the partition table from which we were loaded. 94 * Some boot code (e.g. syslinux) use this info to relocate 95 * themselves, so we want to pass a valid one to the next stage. 96 * NOTE: the use of %si is not a standard. 97 * 98 * This boot block first relocates itself at a different address (0:0x600), 99 * to free the space at 0:0x7c00 for the next stage boot block. 100 * 101 * It then initializes some memory at 0:0x800 and above (pointed by %bp) 102 * to store the original drive number (%dl) passed to us, and to construct a 103 * fake partition entry. The latter is used by the disk I/O routine and, 104 * in some cases, passed in %si to the next stage boot code. 105 * 106 * The variables at 0x1b2 are accessed as negative offsets from %bp. 107 * 108 * After the relocation, the code scans the partition table printing 109 * out enabled partition or disks, and waits for user input. 110 * 111 * When a partition is selected, or a timeout expires, the currently 112 * selected partition is used to load the next stage boot code, 113 * %dl and %si are set appropriately as when we were called, and 114 * control is transferred to the newly loaded code at 0:0x7c00. 115 */ 116 117/* 118 * CONSTANTS 119 * 120 * NHRDRV is the address in segment 0 where the BIOS writes the 121 * total number of hard disks in the system. 122 * LOAD is the original load address and cannot be changed. 123 * ORIGIN is the relocation address. If you change it, you also need 124 * to change the value passed to the linker in the Makefile 125 * PRT_OFF is the location of the partition table (from the MBR standard). 126 * B0_OFF is the location of the data area, known to boot0cfg so 127 * it cannot be changed. Computed as a negative offset from 0x200 128 * MAGIC is the signature of a boot block. 129 */ 130 131 .set NHRDRV,0x475 # Number of hard drives 132 .set ORIGIN,0x600 # Execution address 133 .set LOAD,0x7c00 # Load address 134 135 .set PRT_OFF,0x1be # Partition table 136 .set B0_OFF,(B0_BASE-0x200) # Offset of boot0 data 137 138 .set MAGIC,0xaa55 # Magic: bootable 139 140 .set KEY_ENTER,0x1c # Enter key scan code 141 .set KEY_F1,0x3b # F1 key scan code 142 .set KEY_1,0x02 # #1 key scan code 143 144 .set ASCII_BEL,'#' # ASCII code for <BEL> 145 .set ASCII_CR,0x0D # ASCII code for <CR> 146 147/* 148 * Offsets of variables in the block at B0_OFF, and in the volatile 149 * data area, computed as displacement from %bp. 150 * We need to define them as constant as the assembler cannot 151 * compute them in its single pass. 152 */ 153 .set _NXTDRV, B0_OFF+6 # Next drive 154 .set _OPT, B0_OFF+7 # Default option 155 .set _SETDRV, B0_OFF+8 # Drive to force 156 .set _FLAGS, B0_OFF+9 # Flags 157 .set SETDRV, 0x20 # the 'setdrv' flag 158 .set NOUPDATE, 0x40 # the 'noupdate' flag 159 .set USEPACKET, 0x80 # the 'packet' flag 160 161 /* ticks is at a fixed position */ 162 .set _TICKS, (PRT_OFF - 0x200 - 2) # Timeout ticks 163 .set _MNUOPT, 0x10 # Saved menu entries 164 165 .set TLEN, (desc_ofs - bootable_ids) # size of bootable ids 166 .globl start # Entry point 167 .code16 # This runs in real mode 168 169/* 170 * MAIN ENTRY POINT 171 * Initialise segments and registers to known values. 172 * segments start at 0. 173 * The stack is immediately below the address we were loaded to. 174 * NOTE: the initial section of the code (up to movw $LOAD,%sp) 175 * is used by boot0cfg, together with the 'Drive ' string and 176 * the 0x55, 0xaa at the end, as an identifier for version 1.0 177 * of the boot code. Do not change it. 178 * In version 1.0 the parameter table (_NEXTDRV etc) is at 0x1b9 179 */ 180start: cld # String ops inc 181 xorw %ax,%ax # Zero 182 movw %ax,%es # Address 183 movw %ax,%ds # data 184 movw %ax,%ss # Set up 185 movw $LOAD,%sp # stack 186 187 /* 188 * Copy this code to the address it was linked for, 0x600 by default. 189 */ 190 movw %sp,%si # Source 191 movw $start,%di # Destination 192 movw $0x100,%cx # Word count 193 rep # Relocate 194 movsw # code 195 /* 196 * After the code, (i.e. at %di+0, 0x800) create a partition entry, 197 * initialized to LBA 0 / CHS 0:0:1. 198 * Set %bp to point to the partition and also, with negative offsets, 199 * to the variables embedded in the bootblock (nextdrv and so on). 200 */ 201 movw %di,%bp # Address variables 202 movb $0x8,%cl # Words to clear 203 rep # Zero 204 stosw # them 205 incb -0xe(%di) # Set the S field to 1 206 207 jmp main-LOAD+ORIGIN # Jump to relocated code 208 209main: 210#if defined(SIO) && COMSPEED != 0 211 /* 212 * Init the serial port. bioscom preserves the driver number in DX. 213 */ 214 movw $COMSPEED,%ax # defined by Makefile 215 callw bioscom 216#endif 217 218 /* 219 * If the 'setdrv' flag is set in the boot sector, use the drive 220 * number from the boot sector at 'setdrv_num'. 221 * Optionally, do the same if the BIOS gives us an invalid number 222 * (note though that the override prevents booting from a floppy 223 * or a ZIP/flash drive in floppy emulation). 224 * The test costs 4 bytes of code so it is disabled by default. 225 */ 226 testb $SETDRV,_FLAGS(%bp) # Set drive number? 227#ifndef CHECK_DRIVE /* disable drive checks */ 228 jz save_curdrive # no, use the default 229#else 230 jnz disable_update # Yes 231 testb %dl,%dl # Drive number valid? 232 js save_curdrive # Possibly (0x80 set) 233#endif 234 /* 235 * Disable updates if the drive number is forced. 236 */ 237disable_update: orb $NOUPDATE,_FLAGS(%bp) # Disable updates 238 movb _SETDRV(%bp),%dl # Use stored drive number 239 240 /* 241 * Whatever drive we decided to use, store it at (%bp). The byte 242 * is normally used for the state of the partition (0x80 or 0x00), 243 * but we abuse it as it is very convenient to access at offset 0. 244 * The value is read back after 'check_selection' 245 */ 246save_curdrive: movb %dl, (%bp) # Save drive number 247 pushw %dx # Also in the stack 248#ifdef TEST /* test code, print internal bios drive */ 249 rolb $1, %dl 250 movw $drive, %si 251 call putkey 252#endif 253 callw putn # Print a newline 254 /* 255 * Start out with a pointer to the 4th byte of the first table entry 256 * so that after 4 iterations it's beyond the end of the sector 257 * and beyond a 256 byte boundary. We use the latter trick to check for 258 * end of the loop without using an extra register (see start.5). 259 */ 260 movw $(partbl+0x4),%bx # Partition table (+4) 261 xorw %dx,%dx # Item number 262 263 /* 264 * Loop around on the partition table, printing values until we 265 * pass a 256 byte boundary. 266 */ 267read_entry: movb %ch,-0x4(%bx) # Zero active flag (ch == 0) 268 btw %dx,_FLAGS(%bp) # Entry enabled? 269 jnc next_entry # No 270 movb (%bx),%al # Load type 271 test %al, %al # skip empty partition 272 jz next_entry 273 /* 274 * Scan the table of bootable ids, which starts at %di and has 275 * length TLEN. On a match, %di points to the element following the 276 * match; the corresponding offset to the description is $(TLEN-1) 277 * bytes ahead. If we don't find a match, we hit the 'unknown' entry. 278 */ 279 movw $bootable_ids,%di # Lookup tables 280 movb $(TLEN),%cl # Number of entries 281 repne # Locate 282 scasb # type 283 /* 284 * Get the matching element in the next array. 285 * The byte at $(TLEN-1)(%di) contains the offset of the description 286 * string from %di, so we add the number and print the string. 287 */ 288 addw $(TLEN-1), %di # Adjust 289 movb (%di),%cl # Partition 290 addw %cx,%di # description 291 callw putx # Display it 292 293next_entry: incw %dx # Next item 294 addb $0x10,%bl # Next entry 295 jnc read_entry # Till done 296 /* 297 * We are past a 256 byte boundary: the partition table is finished. 298 * Add one to the drive number and check it is valid. 299 * Note that if we started from a floppy, %dl was 0 so we still 300 * get an entry for the next drive, which is the first Hard Disk. 301 */ 302 popw %ax # Drive number 303 subb $0x80-0x1,%al # Does next 304 cmpb NHRDRV,%al # drive exist? (from BIOS?) 305 jb print_drive # Yes 306 /* 307 * If this is the only drive, don't display it as an option. 308 */ 309 decw %ax # Already drive 0? 310 jz print_prompt # Yes 311 /* 312 * If it was illegal or we cycled through them, go back to drive 0. 313 */ 314 xorb %al,%al # Drive 0 315 /* 316 * Whatever drive we selected, make it an ascii digit and save it 317 * back to the "nxtdrv" location in case we want to save it to disk. 318 * This digit is also part of the printed drive string, so add 0x80 319 * to indicate end of string. 320 */ 321print_drive: addb $'0'|0x80,%al # Save next 322 movb %al,_NXTDRV(%bp) # drive number 323 movw $drive,%di # Display 324 callw putx # item 325 /* 326 * Menu is complete, display a prompt followed by current selection. 327 * 'decw %si' makes the register point to the space after 'Default: ' 328 * so we do not see an extra CRLF on the screen. 329 */ 330print_prompt: movw $prompt,%si # Display 331 callw putstr # prompt 332 movb _OPT(%bp),%dl # Display 333 decw %si # default 334 callw putkey # key 335 jmp start_input # Skip beep 336 337/* 338 * Here we have the code waiting for user input or a timeout. 339 */ 340beep: movb $ASCII_BEL,%al # Input error, print or beep 341 callw putchr 342 343start_input: 344 /* 345 * Actual Start of input loop. Take note of time 346 */ 347 xorb %ah,%ah # BIOS: Get 348 int $0x1a # system time 349 movw %dx,%di # Ticks when 350 addw _TICKS(%bp),%di # timeout 351read_key: 352 /* 353 * Busy loop, looking for keystrokes but keeping one eye on the time. 354 */ 355#ifndef SIO 356 movb $0x1,%ah # BIOS: Check 357 int $0x16 # for keypress 358#else /* SIO */ 359 movb $0x03,%ah # BIOS: Read COM 360 call bioscom 361 testb $0x01,%ah # Check line status 362 # (bit 1 indicates input) 363#endif /* SIO */ 364 jnz got_key # Have input 365 xorb %ah,%ah # BIOS: int 0x1a, 00 366 int $0x1a # get system time 367 cmpw %di,%dx # Timeout? 368 jb read_key # No 369 370 /* 371 * Timed out or default selection 372 */ 373use_default: movb _OPT(%bp),%al # Load default 374 jmp check_selection # Join common code 375 376 /* 377 * Get the keystroke. 378 * ENTER or CR confirm the current selection (same as a timeout). 379 * Otherwise convert F1..F6 (or '1'..'6') to 0..5 and check if the 380 * selection is valid. 381 * The SIO code uses ascii chars, the console code uses scancodes. 382 */ 383got_key: 384#ifndef SIO 385 xorb %ah,%ah # BIOS: int 0x16, 00 386 int $0x16 # get keypress 387 movb %ah,%al # move scan code to %al 388 cmpb $KEY_ENTER,%al 389#else 390 movb $0x02,%ah # BIOS: Receive 391 call bioscom 392 cmpb $ASCII_CR,%al 393#endif 394 je use_default # enter -> default 395 /* 396 * Check if the key is acceptable, and loop back if not. 397 * The console (non-SIO) code looks at scancodes and accepts 398 * both F1..F6 and 1..6 (the latter costs 6 bytes of code), 399 * relying on the fact that F1..F6 have higher scancodes than 1..6 400 * The SIO code only takes 1..6 401 */ 402#ifdef SIO /* SIO mode, use ascii values */ 403 subb $'1',%al # Subtract '1' ascii code 404#else /* console mode -- use scancodes */ 405 subb $KEY_F1,%al /* Subtract F1 scan code */ 406#if !defined(ONLY_F_KEYS) 407 cmpb $0x5,%al # F1..F6 408 jna 3f # Yes 409 subb $(KEY_1 - KEY_F1),%al # Less #1 scan code 410 3: 411#endif /* ONLY_F_KEYS */ 412#endif /* SIO */ 413 cmpb $0x5,%al # F1..F6 or 1..6 ? 414#ifdef PXE /* enable PXE/INT18 using F6 */ 415 jne 1f; 416 int $0x18 # found F6, try INT18 417 1: 418#endif /* PXE */ 419 jae beep # Not in F1..F5, beep 420 421check_selection: 422 /* 423 * We have a selection. If it's a bad selection go back to complain. 424 * The bits in MNUOPT were set when the options were printed. 425 * Anything not printed is not an option. 426 */ 427 cbtw # Extend (%ah=0 used later) 428 btw %ax,_MNUOPT(%bp) # Option enabled? 429 jnc beep # No 430 /* 431 * Save the info in the original tables 432 * for rewriting to the disk. 433 */ 434 movb %al,_OPT(%bp) # Save option 435 436 /* 437 * Make %si and %bx point to the fake partition at LBA 0 (CHS 0:0:1). 438 * Because the correct address is already in %bp, just use it. 439 * Set %dl with the drive number saved in byte 0. 440 * If we have pressed F5 or 5, then this is a good, fake value 441 * to present to the next stage boot code. 442 */ 443 movw %bp,%si # Partition for write 444 movb (%si),%dl # Drive number, saved above 445 movw %si,%bx # Partition for read 446 cmpb $0x4,%al # F5/#5 pressed? 447 pushf # Save results for later 448 je 1f # Yes, F5 449 450 /* 451 * F1..F4 was pressed, so make %bx point to the currently 452 * selected partition, and leave the drive number unchanged. 453 */ 454 shlb $0x4,%al # Point to 455 addw $partbl,%ax # selected 456 xchgw %bx,%ax # partition 457 movb $0x80,(%bx) # Flag active 458 /* 459 * If not asked to do a write-back (flags 0x40) don't do one. 460 * Around the call, save the partition pointer to %bx and 461 * restore to %si which is where the next stage expects it. 462 */ 463 1: pushw %bx # Save 464 testb $NOUPDATE,_FLAGS(%bp) # No updates? 465 jnz 2f # skip update 466 movw $start,%bx # Data to write 467 movb $0x3,%ah # Write sector 468 callw intx13 # to disk 469 2: popw %si # Restore 470 471 /* 472 * If going to next drive, replace drive with selected one. 473 * Remember to un-ascii it. Hey 0x80 is already set, cool! 474 */ 475 popf # Restore %al test results 476 jne 3f # If not F5/#5 477 movb _NXTDRV(%bp),%dl # Next drive 478 subb $'0',%dl # number 479 /* 480 * Load selected bootsector to the LOAD location in RAM. If read 481 * fails or there is no 0x55aa marker, treat it as a bad selection. 482 */ 483 3: movw $LOAD,%bx # Address for read 484 movb $0x2,%ah # Read sector 485 callw intx13 # from disk 486 jc beep # If error 487 cmpw $MAGIC,0x1fe(%bx) # Bootable? 488 jne beep # No 489 pushw %si # Save ptr to selected part. 490 callw putn # Leave some space 491 popw %si # Restore, next stage uses it 492 jmp *%bx # Invoke bootstrap 493 494/* 495 * Display routines 496 * putkey prints the option selected in %dl (F1..F5 or 1..5) followed by 497 * the string at %si 498 * putx: print the option in %dl followed by the string at %di 499 * also record the drive as valid. 500 * putn: print a crlf 501 * putstr: print the string at %si 502 * putchr: print the char in al 503 */ 504 505/* 506 * Display the option and record the drive as valid in the options. 507 * That last point is done using the btsw instruction which does 508 * a test and set. We don't care for the test part. 509 */ 510putx: btsw %dx,_MNUOPT(%bp) # Enable menu option 511 movw $item,%si # Display 512 callw putkey # key 513 movw %di,%si # Display the rest 514 callw putstr # Display string 515 516putn: movw $crlf,%si # To next line 517 jmp putstr 518 519putkey: 520#ifndef SIO 521 movb $'F',%al # Display 522 callw putchr # 'F' 523#endif 524 movb $'1',%al # Prepare 525 addb %dl,%al # digit 526 527putstr.1: callw putchr # Display char 528putstr: lodsb # Get byte 529 testb $0x80,%al # End of string? 530 jz putstr.1 # No 531 andb $~0x80,%al # Clear MSB then print last 532 533putchr: 534#ifndef SIO 535 pushw %bx # Save 536 movw $0x7,%bx # Page:attribute 537 movb $0xe,%ah # BIOS: Display 538 int $0x10 # character 539 popw %bx # Restore 540#else /* SIO */ 541 movb $0x01,%ah # BIOS: Send 542bioscom: 543 pushw %dx # Save 544 xorw %dx,%dx # Use COM1 545 int $0x14 # Character 546 popw %dx # Restore 547#endif /* SIO */ 548 retw # To caller 549 550/* One-sector disk I/O routine */ 551 552/* 553 * %dl: drive, %si partition entry, %es:%bx transfer buffer. 554 * Load the CHS values and possibly the LBA address from the block 555 * at %si, and use the appropriate method to load the sector. 556 * Don't use packet mode for a floppy. 557 */ 558intx13: # Prepare CHS parameters 559 movb 0x1(%si),%dh # Load head 560 movw 0x2(%si),%cx # Load cylinder:sector 561 movb $0x1,%al # Sector count 562 pushw %si # Save 563 movw %sp,%di # Save 564#ifndef CHECK_DRIVE /* floppy support */ 565 testb %dl, %dl # is this a floppy ? 566 jz 1f # Yes, use CHS mode 567#endif 568 testb $USEPACKET,_FLAGS(%bp) # Use packet interface? 569 jz 1f # No 570 pushl $0x0 # Set the 571 pushl 0x8(%si) # LBA address 572 pushw %es # Set the transfer 573 pushw %bx # buffer address 574 push $0x1 # Block count 575 push $0x10 # Packet size 576 movw %sp,%si # Packet pointer 577 decw %ax # Verify off 578 orb $0x40,%ah # Use disk packet 579 1: int $0x13 # BIOS: Disk I/O 580 movw %di,%sp # Restore 581 popw %si # Restore 582 retw # To caller 583 584/* 585 * Various menu strings. 'item' goes after 'prompt' to save space. 586 * Also use shorter versions to make room for the PXE/INT18 code. 587 */ 588#ifdef PXE 589prompt: .ascii "\nBoot:" 590item: .ascii " "; .byte ' '|0x80 591#else 592prompt: .ascii "\nDefault:" 593item: .ascii " "; .byte ' '|0x80 594#endif 595crlf: .ascii "\r"; .byte '\n'|0x80 596 597/* Partition type tables */ 598 599bootable_ids: 600 /* 601 * These values indicate bootable types we know about. 602 * Corresponding descriptions are at desc_ofs: 603 * Entries don't need to be sorted. 604 */ 605 .byte 0x1, 0x6, 0x7, 0xb, 0xc 606#ifndef SAVE_MEMORY 607 .byte 0xe 608#endif 609 .byte 0x83, 0xa5, 0xa6, 0xa9, 0x4 610#ifndef SAVE_MORE_MEMORY 611 .byte 0x5, 0xf 612#endif 613 614desc_ofs: 615 /* 616 * Offsets that match the known types above, used to point to the 617 * actual partition name. The last entry must point to os_misc, 618 * which is used for non-matching names. 619 */ 620 .byte os_dos-. # 1, FAT12 DOS 621 .byte os_dos-. # 6, FAT16 <32M, DOS/WIN 622 .byte os_win-. # 7, FAT16 >=32M Windows 623 .byte os_win-. # 11, FAT32 624 .byte os_win-. # 12, FAT32-LBA 625#ifndef SAVE_MEMORY 626 .byte os_win-. # 14, FAT16-LBA 627#endif 628 .byte os_linux-. # 131, Linux 629 .byte os_freebsd-. # 165, FreeBSD 630 .byte os_bsd-. # 166, OpenBSD 631 .byte os_bsd-. # 169, NetBSD 632 .byte os_dos-. # 4, FAT16 < 32M 633#ifndef SAVE_MORE_MEMORY 634 .byte os_ext-. # 5, DOS Ext 635 .byte os_ext-. # 15, DOS Ext-LBA 636#endif 637 638 .byte os_misc-. # Unknown 639 640 /* 641 * And here are the strings themselves. The last byte of 642 * the string has bit 7 set. 643 */ 644os_misc: .byte '?'|0x80 645os_dos: 646#ifndef SAVE_MEMORY /* DOS string only if room */ 647 .ascii "DO"; .byte 'S'|0x80 648#endif 649os_win: .ascii "WI"; .byte 'N'|0x80 650os_linux: .ascii "Linu"; .byte 'x'|0x80 651os_freebsd: .ascii "Free" 652os_bsd: .ascii "BS"; .byte 'D'|0x80 653#ifndef SAVE_MORE_MEMORY 654os_ext: .ascii "EX"; .byte 'T'|0x80 655#endif 656 657 .org (0x200 + B0_OFF),0x90 658/* 659 * The boot0 version 1.0 parameter table. 660 * Do not move it nor change the "Drive " string, boot0cfg 661 * uses its offset and content to identify the boot sector. 662 * The other fields are sometimes changed before writing back to the drive 663 * Be especially careful that nxtdrv: must come after drive:, as it 664 * is part of the same string. 665 */ 666drive: .ascii "Drive " 667nxtdrv: .byte 0x0 # Next drive number 668opt: .byte 0x0 # Option 669setdrv_num: .byte 0x80 # Drive to force 670flags: .byte FLAGS # Flags 671#ifdef VOLUME_SERIAL 672 .byte 0xa8,0xa8,0xa8,0xa8 # Volume Serial Number 673#endif 674ticks: .word TICKS # Delay 675 676 .org PRT_OFF 677/* 678 * Here is the 64 byte partition table that fdisk would fiddle with. 679 */ 680partbl: .fill 0x40,0x1,0x0 # Partition table 681 .word MAGIC # Magic number 682 .org 0x200 # again, safety check 683endblock: 684