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RE: decstation boot loader

To: Florian Lohoff <flo@rfc822.org>
Subject: RE: decstation boot loader
From: Harald Koerfgen <Harald.Koerfgen@home.ivm.de>
Date: Sun, 27 Aug 2000 19:19:49 +0200 (CEST)
Cc: linux-mips@oss.sgi.com
In-reply-to: <20000826220608.J3009@paradigm.rfc822.org>
Organization: none
Reply-to: Harald Koerfgen <Harald.Koerfgen@home.ivm.de>
Sender: owner-linux-mips@oss.sgi.com
Hi Flo,

On 26-Aug-00 Florian Lohoff wrote:
> i sat down a couple of hours and had a look at current possibilities
> of booting the decstations from HD. I am not much further than
> i was was before - And now i got a couple of questions probably one
> of the more specialised mips hackers might answer.
> 
> - The bootblock of the decstation might contain up to 51 extents
>   to load from the disks.
>
>   1. Do these extents refer to the start of the disk or the start
>      of the probably first partition.

The PROM knows nothing about partitions or such so these extends refer obviously
to the start of the disk.
 
>   2. Do i have to set a checksum in the bootblock or does the checksom
>      only apply to the disklabel

The PROM doesn't even know anything about a checksum.
 
>   3. What binarys is the bootloader able to load. From the BSD sources
>      i guess its only raw instructions.

Yes. "mipsel-linux-objcopy --output-target=binary" is your friend.
 
>   4. Does the MS-DOS disklabel and the DEC bootblock interfer in any
>      kind that its impossible to have a diskloader with MS-DOS Disklabels 

No, that should work as long as the the the boot map is short enough not to
overwrite the partition information.
 
> I rewrote the bootprep.c today to play around with loading different binarys.
> I added the honor of partition information meaning - The new (i call
> it writeboot) looks at the start of the partition and calculates
> the extents relativ to the start of the disk. But still i dont get any
> results. When trying to boot those partitions with any kind of combination
> the prompt only returns to the prom command line.

I have successfully booted Linux kernels with bootprep. Depending on the code 
you
want to load, for example a second stage bootloader, you may need to adjust
"boot_block->loadAddr" and "boot_block->execAddr".
 
> I thought of a bootloader much like the silo - Capable of reading
> an ext2 filesystem via libext2 etc.

That's what I always wanted to do but I never found the time...

-- 
Regards,
Harald

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