[U-Boot-Users] u-boot reloacting to SRAM instead of SDRAM

[Jerry Van Baren <gerald.vanbaren@smiths-aerospace.com>]

agnel juni wrote:
> Hello all,
> 
> We have a requirement in an MPC8540 based custom board,for the board to 
> boot-up independent of SDRAM.
> 
> So, we are trying to map SRAM in place od SDRAM in u-boot. Though we 
> succeeded bringing-up the board with this change, we see the behaviour 
> being very flaky.
> 
> Though the board boots up without SDRAM module (say 2 /10 times), this 
> happens only intitiating the boot-up from BDI.
> Otherwise it hangs while reading the CPU clock or configuring base 
> registers. The board never comes up stand alone.
> 
> I think this happens while reading from Global Data / Initial stack 
> which is supposed to be running from SDRAM , now moved to SRAM.
> 
> I did browse through the u-boot mailing list to see any similar case, 
> but don't and thats the reason I am asking for help.
> 
> So, my question is is it possible to run u-boot by relocating to SRAM 
> instead of SDRAM ?
> 
> Any help is appreciated.
> 
> Thanks
> Junita

I have no 8540 experience, but a few possibilities come to mind:

1) Misconfiguration of the SRAM - is it running as SRAM or is it being 
used as L2 cache?  Half 'n half?  If it is being used as L2 cache and 
you are trying to run out of it, it would be flaky to say the least (I 
doubt half 'n half would work since you would only have 128K, but I 
don't know your system or your build size).

2) Is ECC enabled?  If so, did you initialize it before using it (read 
of uninitialized data will cause ECC failures and likely a quick death, 
depending on when and where it occurs).

3) Size - is your u-boot image and RAM usage less than 256KB?  This 
seems less likely since it runs at all.

gvb