From: John Bradford <john@grabjohn.com>
To: hpa@zytor.com (H. Peter Anvin)
Cc: linux-kernel@vger.kernel.org
Subject: Re: Bootable CD idea
Date: Wed, 30 Apr 2003 20:21:42 +0100 (BST) [thread overview]
Message-ID: <200304301921.h3UJLgCZ001523@81-2-122-30.bradfords.org.uk> (raw)
In-Reply-To: <b8p6b6$tm9$1@cesium.transmeta.com> from "H. Peter Anvin" at Apr 30, 2003 11:57:42 AM
> > > > [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.
next prev parent reply other threads:[~2003-04-30 19:05 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-04-30 11:54 Bootable CD idea John Bradford
2003-04-30 12:21 ` Richard B. Johnson
2003-04-30 12:41 ` John Bradford
2003-04-30 13:14 ` Tomas Szepe
2003-04-30 13:46 ` John Bradford
2003-04-30 13:47 ` Tigran Aivazian
2003-04-30 13:25 ` John Bradford
2003-04-30 18:57 ` H. Peter Anvin
2003-04-30 19:21 ` John Bradford [this message]
2003-04-30 21:18 ` H. Peter Anvin
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