[U-Boot-Users] RE: More On Memory Bank x (nothingness)?

Wolfgang Denk wd at denx.de
Tue Feb 11 01:24:25 CET 2003

In message <NEBBKJPFOLJNBMFNKBIIGEMFDEAA.clh at net1plus.com> you wrote:
> Correct me if I'm wrong, folks, but the way I understand it is this:
> Using DCACHE as initial RAM for Stack, etc, does not require any
> physical RAM backing up the cache.  The cleverness is that the cache
> is being used as a temporary supply of necessary storage before the
> SDRAM controller is setup.  It's beyond the scope of this list to
> expain the details, but you can see how this works by studying the
> cache architecture and operation in the architecture and
> processor-specific manuals.
> OCM is On Chip Memory, which I believe the 405GP has 4K.  It is
> another option for the system designer to use as an initial
> stack/ram area prior to SDRAM being available.  Either option should
> work for you.  Using CS 4 should be fine if your board designers
> haven't used it for something that would cause you grief during the
> initial boot!  It is frequently not used.
> CFG_INIT_RAM_ADDR should be somewhere that won't interfere with your
> processor/board/system design.  The default value you will find in
> any recent u-boot distribution in Walnut405.h should work for you.
> I'd set it to a value larger than your SDRAM module. If you have a
> 64MB SDRAM module, set it above 400_0000.  Just make sure your board
> has no resources that are supposed to respond to that address!  That
> code in start.S has been around a while and should work as is when
> you get the config right.

Chris, thanks for this excellent (and 100% correct)  summary.  May  I
add this to the README file?

Best regards,

Wolfgang Denk

Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
Be careful what you wish for. You never know who will be listening.
                                      - Terry Pratchett, _Soul Music_

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