[U-Boot] Problem with U-Boot with running in RAM

[Wolfgang Denk]

Dear Lasse Skov,

In message <4F4169B21905494EBD47A304F02192C92772357B6B at XCH-HQ-01.kk.local> you wrote:
> 
> The problem is that the U-Boot has a problem when it try to rellocate itself to RAM.
> I know that this could be some timing settings for the SDRAM and the RAM controller.

Not only the timing settings, but also the whole RAM init sequence
must mnatch the reauirements of your RAM chips to the letter. Make
sure to study the chip manufacturer's manual. See the FAQ.

> But the thing is that this is not every time uboot try to relocate itself to RAM.

Random behaviour, yes.

> In the FAQ there is this.
> "Standard memory tests are not effective in identifying this type of problem
> because they do not cause stressful cache burst read/write operations. "
> 
> But what exactly does this mean? On my target I has DDR2 ram.

It means that you cannot stress test RAM by just reading and writing
it. The really critical accesses happen in burst mode, which is during
cache fill / flush operations and DMA.

> And I thought that only bursted mode access was possible to the RAM on 
> DDR2?

Even if you manage to cause a burst, there is still a big difference
whether this is an isolated event, or when you are running burst mode
accesses back-to-back over some time. Compiling a Linux kernel
natively on the target with root file system over NFS gives an
excellent stress test, as you hve both lots of code running and
context switches and cache fills and flushes combined with lots of DMA
(from the network interface) at the same time.

Go back to square one, dig out the RAM chip manual, and re-check your
code. Ideally, have somebody else but the original implementor check
it.

Best regards,

Wolfgang Denk

-- 
DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
: 1.  What is the possibility of this being added in the future?
In the near future, the probability is close to zero. In the  distant
future, I'll be dead, and posterity can do whatever they like... :-)
                                                              - lwall