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Re: prom start

To: linux-mips@linux-mips.org
Subject: Re: prom start
From: Joshua Kinard <kumba@gentoo.org>
Date: Sat, 09 Feb 2013 22:54:48 -0500
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On 02/06/2013 11:05 AM, folkert wrote:
> Hi,
> 
> Is this mailing list also meant for generic mips questions? (if not: any
> suggestions for one that is?)
> 
> If so: I'mm experimenting a bit with mips, specifically on SGI hardware
> (Indigo). Now it seems all mips systems have the prom at 0xbfc00000. But
> how does it start? The first 0x3c0 bytes seem to be nonsense. Somewhere
> on the web I found that 0xbfc00884 is the starting point but after
> single stepping 5 instructions, the program counter jumps to 0x00000000
> so I don't think that's the right one either. Also, reading the first 4
> bytes from bfc00000 and using that as a pointer seems to be invalid too:
> 0bf000f0.
> Anyone with insights regarding the booting of the prom on sgi systems?
> 
> 
> Regards,
> 
> Folkert van Heusden

The first Indigo?  IP12?  Or the Indigo2 series (IP22, IP26, or IP28)?

ARCS (the SGI prom) is a bit of black magic and voodoo.  It also terrifies
the priests of Ancient Mu.

You might want to hunt down copies of the PROM images for other SGI systems,
such as IP22, IP32 (O2), IP30 (Octane) (the latter two are on certain IRIX
media) and analyze those in a disassembler and see if you can discern
something from there.

You might also try gxemul and see if it can boot one of those proms (it's a
machine emulator like Qemu, but has some code tailored to SGI hardware in
it).  Might give you some additional insight.

Would be curious about your results if you can learn anything else from it
via your own work.

-- 
Joshua Kinard
Gentoo/MIPS
kumba@gentoo.org
4096R/D25D95E3 2011-03-28

"The past tempts us, the present confuses us, the future frightens us.  And
our lives slip away, moment by moment, lost in that vast, terrible in-between."

--Emperor Turhan, Centauri Republic

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