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List:       linux-arm-kernel
Subject:    Re: XIP?
From:       "Dan Post" <djp.arm () onemyth ! net>
Date:       2004-04-26 16:30:31
Message-ID: 20040426163031.M21236 () onemyth ! net
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On Tue, 20 Apr 2004 17:06:35 -0500, Mark Beckwith wrote
> Thanks for all the help guys.  I talked to my hardware dude and was 
> able to increase the flash size so holding the kernel and filesystem 
> is not a problem.  I still have limited ram so XIP is a requirement. 
>  I am using an Atmel AT91RM9200.  I suggest I start with Nicolas' 
> patch above.  Agreed?

Nicolas' patch is definitely a good place to start.  Contrary to what many
people have posted, XIP is indeed real and working.  It is also NOT slow (on
anything I've worked with (PXA) anyway).

The kernel does XIP.  That's pretty easy to do, and can easily fit under 1.6
MB, much much less if you don't have a lot of drivers and subsystems to load.
 I haven't yet seen how small I can get it as I usually have 32MiB of flash to
play with.  So that number could probably be reduced by quite a bit.  And I
haven't touched uClinux--maybe that will help.

CRAMFS does XIP for binaries (and other files if you really want it).  You
should really look into it.  It's quite easy to use and quite mature.

If you need a user read-write filesystem as well as XIPing the kernel and user
binaries... well, it depends on what flash you have.  Check the MTD mailing
list archives for a XIP-SW/RWW (software read while write/erase) patch.  It
works quite well depending on what flash you use.  If you use anything other
than Intel NOR flash, you will need to port parts of the solution into your
flash driver.  Otherwise it works great!

I've done quite a bit with XIP, so if you have any questions feel free to
email me.

Cheers,
Dan

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