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    SubjectRe: Bootable CD idea
    Date
    > > > > [1] I originally thought that the 2.4 kernel's in-built floppy
    > > > > bootloader used BIOS calls to access the disk, and that a 2.4 kernel
    > > > > image as the El-Torito boot image would work, as the kernel would be
    > > > > accessing the emulated disk, but it didn't seem to when I tried it
    > > > > just now - it failed with an error saying something along the lines of
    > > > > it had run out of data to decompress.
    > > >
    > > > when you did "make bzImage", are you sure you didn't get the message about
    > > > the kernel being too big for floppy booting?
    > >
    > > No, I've just checked - the same kernel image boots fine from a real floppy.
    > >
    >
    > The boot sector bootloader is broken for anything but genuine legacy
    > floppies, because it relies on getting the proper sector not found in
    > order to determine the geometry. Most LBA<->CHS conversions -- and
    > that includes El Torito, IDE floppies, USB floppies, and just about
    > anything else that isn't a classical legacy floppy -- simply spill
    > into the next track, confusing bootsect.S. This is part of why
    > bootsect.S is gone in 2.5.

    Ah, it makes more sense now :-). So, could I bodge 2.4 in to working
    by modifying bootsect.S with something like this?


    movw $disksizes+1, %si # Force 18 sectors/track
    probe_loop:
    lodsb
    cbtw # extend to word
    xchgw %cx, %ax # %cx = track and sector
    xorw %dx, %dx # drive 0, head 0
    movw $0x0200, %bx # address = 512, in INITSEG (%es = %cs)
    movw $0x0201, %ax # service 2, 1 sector
    int $0x13
    movb $0x03, %ah # read cursor pos
    xorb %bh, %bh

    John.
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