440GX MMU problem

[VanBaren, Gerald (AGRE)]

> -----Original Message-----
> From: linuxppc-embedded-bounces at ozlabs.org
> [mailto:linuxppc-embedded-bounces at ozlabs.org] On Behalf Of
> Barbier, Renaud (GE Infrastructure)
> Sent: Friday, December 03, 2004 3:53 PM
> To: Matt Porter
> Cc: linuxppc-embedded at ozlabs.org
> Subject: RE: 440GX MMU problem
>
> actually, I just loaded linux at memory offset
> 0x10000000(above 256MB) and in this case it is able to boot
> and use the full 512MB.
> there maybe indeed something broken.
>
> Originally, U-boot did not map the full 512MB but only 256MB.
> I wonder if that could be a possible source of my problem.

Disclaimer: I don't have experience with the 4xx family, but won't stop
me from speculating (which drives Wolfgang crazy when I guess wrong ;-).

On the 82xx u-boot uses BATs to map memory.  On the 82xx, BATs are
limited to 256MBytes per BAT.  I'm guessing you are running into this.
Somewhere in your u-boot it doesn't know how to go beyond the 256MByte
boundary.

On u-boot, check out the use of "CONFIG_VERY_BIG_RAM".  It doesn't look
like it applies directly to your board/processor, but you may be able to
enhance your system using it or a similar concept.

gvb


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