Memory POST Test - Timing

[Brownlie, Lewis]

Hello all,

>From everything I have read, the memory POST test runs before U-Boot relocates to RAM.

               For example, README.POST states the following (emphasis added by me):

Also, all tests will be discriminated by the moment they run at.
Specifically, the following groups will be singled out:

  1) Tests running before relocating to RAM

     These tests will run immediately after initializing RAM
     as to enable modifying it without taking care of its
     contents. Basically, this group will contain memory tests
     only.

  2) Tests running after relocating to RAM

     These tests will run immediately before entering the main
     loop as to guarantee full hardware initialization.

               Another example, in the U-Boot mailing list archives, in the message titled "POST Memory Test Problem," Wolfgang Denk wrote (Dec 22, 2014):

In case it is not obvious: you cannot run a memory test on the memory
you are running from.  You must make sure to run the POST memory test
_before_ relocation to RAM.

However, in trying to get the memory POST test to work myself, I emailed the U-Boot mailing list for help (my message was titled "U-Boot Fails w/ Memory Test"), and Heinrich replied; part of his reply was:


The test must run *after* relocation. Otherwise we will overwrite U-Boot.

When I tried running the test after relocation, the it worked, whereas it didn't before.

Thus, my question is, why did Heinrich say that my test must run after relocation, and why did this work; when everything else I've read says it must run before relocation?

Thank you,
-Lewis