[U-Boot] boot from ram on rd-6281-a

[Wolfgang Wegner]

Dear Juergen,

On Fri, Feb 26, 2010 at 12:16:22PM +0100, Juergen Schindele wrote:
> Am Freitag, 26. Februar 2010 schrieb Wolfgang Denk:
> > Dear Juergen Schindele,
> > 
> > In message <201002261056.32502.schindele at nentec.de> you wrote:
> > >
> > > i need a different bootloader than the one installed.
> > > so i tried to develop a private one by loading it to RAM.
> > > So i modified the TEXT_BASE = 0x00400000
> > > to not collide with the installed one.
> > 
> > This is not enough. You must also make sure not to try to perform all
> > the low level initializations again that have already been done.
> I know that, but SKIP_LOW_LEVEL_INIT is defined because 
> register init is done with kirkwood boot header for booting from
> SPI/NAND-Flash. I dont see other blocking points. :-(
> i tried to skip relocate too but it did not help !

I have absolutely no experience concerning kirkwood, but did the same
for coldfire for running U-Boot as the flasher application started
from the debugger...
IIRC there were three places I had to change for coldfire:
- low-level init: do not put the vector table at the beginning
  of code (probably better: initialize it in the proper place?)
- leave the vector base register as it is (should be set up
  properly by first loader/debugger, and U-Boot does not use
  interrupts)
- the cpu speed detection/setting code was basically switched back to
  detection for CONFIG_MONITOR_IS_IN_RAM because it involved putting
  the RAM to self-refresh, which is obviously not possible when running
  from it

(For Coldfire, a special case was that I had to disable monitor
protection manually because the standard condition fails due to the
memory layout.)

Here's my patch for Coldfire MCF532x/7x:
http://www.mail-archive.com/u-boot@lists.denx.de/msg28779.html

BTW, disabling relocation may lead to bad results for malloc and
the initial stack setup. I am not sure but seem to remember I
had some problems when I tried it - and, it should not be a problem
to do it as usual anyways if everything else is working correctly.

Hope this can give some useful hints,
Wolfgang