199767f8919635c4928607450d9e0abb932109ceToomas Soome * Copyright (c) 2008 Luigi Rizzo (mostly documentation)
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Copyright (c) 2002 Bruce M. Simpson
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Copyright (c) 1998 Robert Nordier
199767f8919635c4928607450d9e0abb932109ceToomas Soome * All rights reserved.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Redistribution and use in source and binary forms are freely
199767f8919635c4928607450d9e0abb932109ceToomas Soome * permitted provided that the above copyright notice and this
199767f8919635c4928607450d9e0abb932109ceToomas Soome * paragraph and the following disclaimer are duplicated in all
199767f8919635c4928607450d9e0abb932109ceToomas Soome * such forms.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * This software is provided "AS IS" and without any express or
199767f8919635c4928607450d9e0abb932109ceToomas Soome * implied warranties, including, without limitation, the implied
199767f8919635c4928607450d9e0abb932109ceToomas Soome * warranties of merchantability and fitness for a particular
199767f8919635c4928607450d9e0abb932109ceToomas Soome/* build options: */
199767f8919635c4928607450d9e0abb932109ceToomas Soome#ifdef PXE /* enable PXE/INT18 booting with F6 */
199767f8919635c4928607450d9e0abb932109ceToomas Soome#ifdef CHECK_DRIVE /* make sure we boot from a HD. */
199767f8919635c4928607450d9e0abb932109ceToomas Soome#ifdef ONLY_F_KEYS /* Only F1..F6, no digits on console */
199767f8919635c4928607450d9e0abb932109ceToomas Soome#ifdef VOLUME_SERIAL /* support Volume serial number */
199767f8919635c4928607450d9e0abb932109ceToomas Soome#define B0_BASE 0x1ae /* move the internal data area */
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Note - this code uses many tricks to save space and fit in one sector.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * This includes using side effects of certain instructions, reusing
199767f8919635c4928607450d9e0abb932109ceToomas Soome * register values from previous operations, etc.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Be extremely careful when changing the code, even for simple things.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * BOOT BLOCK STRUCTURE
199767f8919635c4928607450d9e0abb932109ceToomas Soome * This code implements a Master Boot Record (MBR) for an Intel/PC disk.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * It is 512 bytes long and it is normally loaded by the BIOS (or another
199767f8919635c4928607450d9e0abb932109ceToomas Soome * bootloader) at 0:0x7c00. This code depends on %cs:%ip being 0:0x7c00
199767f8919635c4928607450d9e0abb932109ceToomas Soome * The initial chunk of instructions is used as a signature by external
199767f8919635c4928607450d9e0abb932109ceToomas Soome * tools (e.g. boot0cfg) which can manipulate the block itself.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * The area at offset 0x1b2 contains a magic string ('Drive '), also
199767f8919635c4928607450d9e0abb932109ceToomas Soome * used as a signature to detect the block, and some variables that can
199767f8919635c4928607450d9e0abb932109ceToomas Soome * be updated by boot0cfg (and optionally written back to the disk).
199767f8919635c4928607450d9e0abb932109ceToomas Soome * These variables control the operation of the bootloader itself,
199767f8919635c4928607450d9e0abb932109ceToomas Soome * e.g. which partitions to enable, the timeout, the use of LBA
199767f8919635c4928607450d9e0abb932109ceToomas Soome * (called 'packet') or CHS mode, whether to force a drive number,
199767f8919635c4928607450d9e0abb932109ceToomas Soome * and whether to write back the user's selection back to disk.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * As in every Master Boot Record, the partition table is at 0x1be,
199767f8919635c4928607450d9e0abb932109ceToomas Soome * made of four 16-byte entries each containing:
199767f8919635c4928607450d9e0abb932109ceToomas Soome * OFF SIZE DESCRIPTION
199767f8919635c4928607450d9e0abb932109ceToomas Soome * 0 1 status (0x80: bootable, 0: non bootable)
199767f8919635c4928607450d9e0abb932109ceToomas Soome * 1 3 start sector CHS
199767f8919635c4928607450d9e0abb932109ceToomas Soome * 8:head, 6:sector, 2:cyl bit 9..8, 8:cyl bit 7..0
199767f8919635c4928607450d9e0abb932109ceToomas Soome * 4 1 partition type
199767f8919635c4928607450d9e0abb932109ceToomas Soome * 5 3 end sector CHS
199767f8919635c4928607450d9e0abb932109ceToomas Soome * 8 4 LBA of first sector
199767f8919635c4928607450d9e0abb932109ceToomas Soome * 12 4 partition size in sectors
199767f8919635c4928607450d9e0abb932109ceToomas Soome * and followed by the two bytes 0x55, 0xAA (MBR signature).
199767f8919635c4928607450d9e0abb932109ceToomas Soome * BOOT BLOCK OPERATION
199767f8919635c4928607450d9e0abb932109ceToomas Soome * On entry, the registers contain the following values:
199767f8919635c4928607450d9e0abb932109ceToomas Soome * %cs:%ip 0:0x7c00
199767f8919635c4928607450d9e0abb932109ceToomas Soome * %dl drive number (0x80, 0x81, ... )
199767f8919635c4928607450d9e0abb932109ceToomas Soome * %si pointer to the partition table from which we were loaded.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Some boot code (e.g. syslinux) use this info to relocate
199767f8919635c4928607450d9e0abb932109ceToomas Soome * themselves, so we want to pass a valid one to the next stage.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * NOTE: the use of %si is not a standard.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * This boot block first relocates itself at a different address (0:0x600),
199767f8919635c4928607450d9e0abb932109ceToomas Soome * to free the space at 0:0x7c00 for the next stage boot block.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * It then initializes some memory at 0:0x800 and above (pointed by %bp)
199767f8919635c4928607450d9e0abb932109ceToomas Soome * to store the original drive number (%dl) passed to us, and to construct a
199767f8919635c4928607450d9e0abb932109ceToomas Soome * fake partition entry. The latter is used by the disk I/O routine and,
199767f8919635c4928607450d9e0abb932109ceToomas Soome * in some cases, passed in %si to the next stage boot code.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * The variables at 0x1b2 are accessed as negative offsets from %bp.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * After the relocation, the code scans the partition table printing
199767f8919635c4928607450d9e0abb932109ceToomas Soome * out enabled partition or disks, and waits for user input.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * When a partition is selected, or a timeout expires, the currently
199767f8919635c4928607450d9e0abb932109ceToomas Soome * selected partition is used to load the next stage boot code,
199767f8919635c4928607450d9e0abb932109ceToomas Soome * %dl and %si are set appropriately as when we were called, and
199767f8919635c4928607450d9e0abb932109ceToomas Soome * control is transferred to the newly loaded code at 0:0x7c00.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * NHRDRV is the address in segment 0 where the BIOS writes the
199767f8919635c4928607450d9e0abb932109ceToomas Soome * total number of hard disks in the system.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * LOAD is the original load address and cannot be changed.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * ORIGIN is the relocation address. If you change it, you also need
199767f8919635c4928607450d9e0abb932109ceToomas Soome * to change the value passed to the linker in the Makefile
199767f8919635c4928607450d9e0abb932109ceToomas Soome * PRT_OFF is the location of the partition table (from the MBR standard).
199767f8919635c4928607450d9e0abb932109ceToomas Soome * B0_OFF is the location of the data area, known to boot0cfg so
199767f8919635c4928607450d9e0abb932109ceToomas Soome * it cannot be changed. Computed as a negative offset from 0x200
199767f8919635c4928607450d9e0abb932109ceToomas Soome * MAGIC is the signature of a boot block.
199767f8919635c4928607450d9e0abb932109ceToomas Soome .set B0_OFF,(B0_BASE-0x200) # Offset of boot0 data
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Offsets of variables in the block at B0_OFF, and in the volatile
199767f8919635c4928607450d9e0abb932109ceToomas Soome * data area, computed as displacement from %bp.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * We need to define them as constant as the assembler cannot
199767f8919635c4928607450d9e0abb932109ceToomas Soome * compute them in its single pass.
199767f8919635c4928607450d9e0abb932109ceToomas Soome /* ticks is at a fixed position */
199767f8919635c4928607450d9e0abb932109ceToomas Soome .set _TICKS, (PRT_OFF - 0x200 - 2) # Timeout ticks
199767f8919635c4928607450d9e0abb932109ceToomas Soome .set TLEN, (desc_ofs - bootable_ids) # size of bootable ids
199767f8919635c4928607450d9e0abb932109ceToomas Soome * MAIN ENTRY POINT
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Initialise segments and registers to known values.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * segments start at 0.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * The stack is immediately below the address we were loaded to.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * NOTE: the initial section of the code (up to movw $LOAD,%sp)
199767f8919635c4928607450d9e0abb932109ceToomas Soome * is used by boot0cfg, together with the 'Drive ' string and
199767f8919635c4928607450d9e0abb932109ceToomas Soome * the 0x55, 0xaa at the end, as an identifier for version 1.0
199767f8919635c4928607450d9e0abb932109ceToomas Soome * of the boot code. Do not change it.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * In version 1.0 the parameter table (_NEXTDRV etc) is at 0x1b9
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Copy this code to the address it was linked for, 0x600 by default.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * After the code, (i.e. at %di+0, 0x800) create a partition entry,
199767f8919635c4928607450d9e0abb932109ceToomas Soome * initialized to LBA 0 / CHS 0:0:1.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Set %bp to point to the partition and also, with negative offsets,
199767f8919635c4928607450d9e0abb932109ceToomas Soome * to the variables embedded in the bootblock (nextdrv and so on).
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Init the serial port. bioscom preserves the driver number in DX.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * If the 'setdrv' flag is set in the boot sector, use the drive
199767f8919635c4928607450d9e0abb932109ceToomas Soome * number from the boot sector at 'setdrv_num'.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Optionally, do the same if the BIOS gives us an invalid number
199767f8919635c4928607450d9e0abb932109ceToomas Soome * (note though that the override prevents booting from a floppy
199767f8919635c4928607450d9e0abb932109ceToomas Soome * or a ZIP/flash drive in floppy emulation).
199767f8919635c4928607450d9e0abb932109ceToomas Soome * The test costs 4 bytes of code so it is disabled by default.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Disable updates if the drive number is forced.
199767f8919635c4928607450d9e0abb932109ceToomas Soomedisable_update: orb $NOUPDATE,_FLAGS(%bp) # Disable updates
199767f8919635c4928607450d9e0abb932109ceToomas Soome movb _SETDRV(%bp),%dl # Use stored drive number
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Whatever drive we decided to use, store it at (%bp). The byte
199767f8919635c4928607450d9e0abb932109ceToomas Soome * is normally used for the state of the partition (0x80 or 0x00),
199767f8919635c4928607450d9e0abb932109ceToomas Soome * but we abuse it as it is very convenient to access at offset 0.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * The value is read back after 'check_selection'
199767f8919635c4928607450d9e0abb932109ceToomas Soomesave_curdrive: movb %dl, (%bp) # Save drive number
199767f8919635c4928607450d9e0abb932109ceToomas Soome#ifdef TEST /* test code, print internal bios drive */
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Start out with a pointer to the 4th byte of the first table entry
199767f8919635c4928607450d9e0abb932109ceToomas Soome * so that after 4 iterations it's beyond the end of the sector
199767f8919635c4928607450d9e0abb932109ceToomas Soome * and beyond a 256 byte boundary. We use the latter trick to check for
199767f8919635c4928607450d9e0abb932109ceToomas Soome * end of the loop without using an extra register (see start.5).
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Loop around on the partition table, printing values until we
199767f8919635c4928607450d9e0abb932109ceToomas Soome * pass a 256 byte boundary.
199767f8919635c4928607450d9e0abb932109ceToomas Soomeread_entry: movb %ch,-0x4(%bx) # Zero active flag (ch == 0)
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Scan the table of bootable ids, which starts at %di and has
199767f8919635c4928607450d9e0abb932109ceToomas Soome * length TLEN. On a match, %di points to the element following the
199767f8919635c4928607450d9e0abb932109ceToomas Soome * match; the corresponding offset to the description is $(TLEN-1)
199767f8919635c4928607450d9e0abb932109ceToomas Soome * bytes ahead. We use a count of TLEN+1 so if we don't find a match
199767f8919635c4928607450d9e0abb932109ceToomas Soome * within the first TLEN entries, we hit the 'unknown' entry.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Get the matching element in the next array.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * The byte at $(TLEN-1)(%di) contains the offset of the description
199767f8919635c4928607450d9e0abb932109ceToomas Soome * string from %di, so we add the number and print the string.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * We are past a 256 byte boundary: the partition table is finished.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Add one to the drive number and check it is valid.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Note that if we started from a floppy, %dl was 0 so we still
199767f8919635c4928607450d9e0abb932109ceToomas Soome * get an entry for the next drive, which is the first Hard Disk.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * If this is the only drive, don't display it as an option.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * If it was illegal or we cycled through them, go back to drive 0.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Whatever drive we selected, make it an ascii digit and save it
199767f8919635c4928607450d9e0abb932109ceToomas Soome * back to the "nxtdrv" location in case we want to save it to disk.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * This digit is also part of the printed drive string, so add 0x80
199767f8919635c4928607450d9e0abb932109ceToomas Soome * to indicate end of string.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Menu is complete, display a prompt followed by current selection.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * 'decw %si' makes the register point to the space after 'Boot: '
199767f8919635c4928607450d9e0abb932109ceToomas Soome * so we do not see an extra CRLF on the screen.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Here we have the code waiting for user input or a timeout.
199767f8919635c4928607450d9e0abb932109ceToomas Soomebeep: movb $ASCII_BEL,%al # Input error, print or beep
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Actual Start of input loop. Take note of time
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Busy loop, looking for keystrokes but keeping one eye on the time.
199767f8919635c4928607450d9e0abb932109ceToomas Soome#else /* SIO */
199767f8919635c4928607450d9e0abb932109ceToomas Soome#endif /* SIO */
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Timed out or default selection
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Get the keystroke.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * ENTER or CR confirm the current selection (same as a timeout).
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Otherwise convert F1..F6 (or '1'..'6') to 0..5 and check if the
199767f8919635c4928607450d9e0abb932109ceToomas Soome * selection is valid.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * The SIO code uses ascii chars, the console code uses scancodes.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Check if the key is acceptable, and loop back if not.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * The console (non-SIO) code looks at scancodes and accepts
199767f8919635c4928607450d9e0abb932109ceToomas Soome * both F1..F6 and 1..6 (the latter costs 6 bytes of code),
199767f8919635c4928607450d9e0abb932109ceToomas Soome * relying on the fact that F1..F6 have higher scancodes than 1..6
199767f8919635c4928607450d9e0abb932109ceToomas Soome * The SIO code only takes 1..6
199767f8919635c4928607450d9e0abb932109ceToomas Soome#else /* console mode -- use scancodes */
199767f8919635c4928607450d9e0abb932109ceToomas Soome#endif /* ONLY_F_KEYS */
199767f8919635c4928607450d9e0abb932109ceToomas Soome#endif /* SIO */
199767f8919635c4928607450d9e0abb932109ceToomas Soome#endif /* PXE */
199767f8919635c4928607450d9e0abb932109ceToomas Soome * We have a selection. If it's a bad selection go back to complain.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * The bits in MNUOPT were set when the options were printed.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Anything not printed is not an option.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Save the info in the original tables
199767f8919635c4928607450d9e0abb932109ceToomas Soome * for rewriting to the disk.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Make %si and %bx point to the fake partition at LBA 0 (CHS 0:0:1).
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Because the correct address is already in %bp, just use it.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Set %dl with the drive number saved in byte 0.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * If we have pressed F5 or 5, then this is a good, fake value
199767f8919635c4928607450d9e0abb932109ceToomas Soome * to present to the next stage boot code.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * F1..F4 was pressed, so make %bx point to the currently
199767f8919635c4928607450d9e0abb932109ceToomas Soome * selected partition, and leave the drive number unchanged.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * If not asked to do a write-back (flags 0x40) don't do one.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Around the call, save the partition pointer to %bx and
199767f8919635c4928607450d9e0abb932109ceToomas Soome * restore to %si which is where the next stage expects it.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * If going to next drive, replace drive with selected one.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Remember to un-ascii it. Hey 0x80 is already set, cool!
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Load selected bootsector to the LOAD location in RAM. If read
199767f8919635c4928607450d9e0abb932109ceToomas Soome * fails or there is no 0x55aa marker, treat it as a bad selection.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Display routines
199767f8919635c4928607450d9e0abb932109ceToomas Soome * putkey prints the option selected in %dl (F1..F5 or 1..5) followed by
199767f8919635c4928607450d9e0abb932109ceToomas Soome * the string at %si
199767f8919635c4928607450d9e0abb932109ceToomas Soome * putx: print the option in %dl followed by the string at %di
199767f8919635c4928607450d9e0abb932109ceToomas Soome * also record the drive as valid.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * putn: print a crlf
199767f8919635c4928607450d9e0abb932109ceToomas Soome * putstr: print the string at %si
199767f8919635c4928607450d9e0abb932109ceToomas Soome * putchr: print the char in al
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Display the option and record the drive as valid in the options.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * That last point is done using the btsw instruction which does
199767f8919635c4928607450d9e0abb932109ceToomas Soome * a test and set. We don't care for the test part.
199767f8919635c4928607450d9e0abb932109ceToomas Soomeputx: btsw %dx,_MNUOPT(%bp) # Enable menu option
199767f8919635c4928607450d9e0abb932109ceToomas Soome#else /* SIO */
199767f8919635c4928607450d9e0abb932109ceToomas Soome#endif /* SIO */
199767f8919635c4928607450d9e0abb932109ceToomas Soome/* One-sector disk I/O routine */
199767f8919635c4928607450d9e0abb932109ceToomas Soome * %dl: drive, %si partition entry, %es:%bx transfer buffer.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Load the CHS values and possibly the LBA address from the block
199767f8919635c4928607450d9e0abb932109ceToomas Soome * at %si, and use the appropriate method to load the sector.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Don't use packet mode for a floppy.
199767f8919635c4928607450d9e0abb932109ceToomas Soome testb $USEPACKET,_FLAGS(%bp) # Use packet interface?
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Various menu strings. 'item' goes after 'prompt' to save space.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Also use shorter versions to make room for the PXE/INT18 code.
199767f8919635c4928607450d9e0abb932109ceToomas Soome/* Partition type tables */
199767f8919635c4928607450d9e0abb932109ceToomas Soome * These values indicate bootable types we know about.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Corresponding descriptions are at desc_ofs:
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Entries don't need to be sorted.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Offsets that match the known types above, used to point to the
199767f8919635c4928607450d9e0abb932109ceToomas Soome * actual partition name. The last entry must point to os_misc,
199767f8919635c4928607450d9e0abb932109ceToomas Soome * which is used for non-matching names.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * And here are the strings themselves. The last byte of
199767f8919635c4928607450d9e0abb932109ceToomas Soome * the string has bit 7 set.
199767f8919635c4928607450d9e0abb932109ceToomas Soome#ifndef SAVE_MORE_MEMORY /* 'DOS' remapped to 'WIN' if no room */
199767f8919635c4928607450d9e0abb932109ceToomas Soome * The boot0 version 1.0 parameter table.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Do not move it nor change the "Drive " string, boot0cfg
199767f8919635c4928607450d9e0abb932109ceToomas Soome * uses its offset and content to identify the boot sector.
199767f8919635c4928607450d9e0abb932109ceToomas Soome * The other fields are sometimes changed before writing back to the drive
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Be especially careful that nxtdrv: must come after drive:, as it
199767f8919635c4928607450d9e0abb932109ceToomas Soome * is part of the same string.
199767f8919635c4928607450d9e0abb932109ceToomas Soome .byte 0xa8,0xa8,0xa8,0xa8 # Volume Serial Number
199767f8919635c4928607450d9e0abb932109ceToomas Soome * Here is the 64 byte partition table that fdisk would fiddle with.