[U-Boot-Users] PPC8xx chip select configuration at startup

[Steve Strublic]

Hi Wolfgang,

If I had a choice in using a boot address other than 0, I would use it,
but this is a porting effort to an existing platform.  I do not have a
way to change it.  So I'm stuck with what I've got.

And here's a snippet from the README that led me to the conclusion that
this was common:

>System Initialization:
>----------------------
> In the reset configuration, U-Boot starts at the reset entry point
> (on most PowerPC systems at address 0x00000100). Because of the reset
> configuration for CS0# this is a mirror of the onboard Flash memory.
> To be able to re-map memory U-Boot then jumps to its link address.

So to say that this is completely wrong seems a little strong.  What
part am I specifically wrong about?

Believe me, I have little desire to modify a known, stable, widely
available system that operates on a multitude of platforms and
processors.  I just want to get it right.  I've read the README
extensively and thanks to it I've gotten everything else straight; just
this one item is causing me problems.  Can you give me a hint as to
where in the README I should look to find the information that resolves
this issue?

Thanks,

Steve

-----Original Message-----
From: wd at denx.de [mailto:wd at denx.de] 
Sent: Thursday, February 16, 2006 5:07 PM
To: Steve Strublic
Cc: u-boot-users at lists.sourceforge.net
Subject: Re: [U-Boot-Users] PPC8xx chip select configuration at startup 

In message
<482F3C06ECF00C44AEC226520C6FCB1A51ECB6 at EXCHANGEVS.HYPERCOM.COM> you
wrote:
> 
> My board boots to address 0x0, with FLASH located there.  The desired
> location for FLASH memory will be at 0x0400_0000.  This is the address

I recommend NOT to use such a low address.

> space to which I link U-Boot.  The way I understand U-Boot to work is
> that for PPC8xx platforms, FLASH memory is generally located at
address
> 0x0, and CS0 is required to map both address 0x0 and your absolute
> address space (0x0400_0000 in my example) so it can seamlessly jump
from

No, this is completely wrong.

> that are contrary to what I require.  What I ended up doing is program
> CS0 base and option registers with what I call 'boot' values, to
> correctly configure OR0 to allow this duplication of address space for

Please read the README. It's all dicumented there.

Best regards,

Wolfgang Denk

-- 
Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
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