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List:       linux-arm-kernel
Subject:    Re: XIP?
From:       Matthias Welwarsky <mwelwarsky () web ! de>
Date:       2004-04-20 8:10:04
Message-ID: 200404201010.04757.mwelwarsky () web ! de
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On Monday 19 April 2004 19:22, Mark Beckwith wrote:
> Hi guys, I just got informed from my client that:
>
> "XIP is CRITICAL to this project.  If this won't work, we need to know it
> ASAP and will need to re-evaluate our approach.  Resolving the issues with
> XIP needs to be your top priority, above trying to reduce code size or
> working on additional drivers."
>
> The target platform has 2M of flash and 2M of Ram.  From what I've read so
> far about XIP on arm, its a lot of work and its not going to save me anyway
> (its not a silver bullet).  So, do I have a prayer?  Any thoughts would be
> appreciated.

That's quite tight ;) I'd say you have no chance to run a regular linux on 
that platform, but uClinux might be a candidate. Try www.uclinux.org. Its 
track record of running on very small machines is quite good.

XIP for ARM is not available as free software, but I heard of a commercial 
version sold by the former RidgeRun people (not cheap, but affordable). 
Wonder about the license, though.

Still, an uncompressed uClinux kernel uses up to 1M of memory, so you have to 
squeeze the root filesystem into about 1M of flash memory. Uncompressed, due 
to XIP. Probably enough for a single application and some devnodes.

See that you chose a CPU with at least an I cache, because execution from 
flash is _really_ slow.

regards,
	matthias
 

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