[U-Boot] Chain loading an u-boot from an u-boot

[Andreas Bießmann]

Hi Helmut,

On 02/12/2014 10:56 AM, Helmut Raiger wrote:
>> I understand the first two points, but why do you store the kernel again
>> with 1bit HW-ECC ? The second U-Boot is able to check with 4bit BCH and
>> your NAND requires 4bit.
> 
> This is mainly due to performance requirements. Using 4bit BCH
> increases overhead and makes DMA (currently not used in the
> kernel driver) a lot slower. We thought we might slip through with
> 1bit HW-ECC, but we will test this (hopefully not in the field this time
> ;-) )

If your HW requires 4Bit it is highly recommended to do so. You will run
your HW out of specs in other case and I think it is hard to qualify
that 4Bit required ECC runs with 1Bit ECC and UBIFS as you stated in a
previous mail.

>> I agree with Andreas' analyses. It seems that the second u-boot
>> overwrites your running U-Boot and only if they are identical you have
>> no problem, that means that you are not changing the running code.
> I double-checked now, the running u-boot is not overwritten.
> When the 2nd u-boot relocates it overwrites the first one, but
> that shouldn't be a problem. The first u-boot keeps working after
> loading (but not running) the second one without issues.
> 
> Only the 'go' crashes the system. u-boot starts stand-alone
> application fine, just as the kernel. I really can't see the point
> why another u-boot should be any different?!

Just thinking ... have you checked the global data pointer? Is it
possible that the global data of the first u-boot influences the global
data of the second one?

Best regards

Andreas Bießmann