[coreboot] How to test RAM beyond 640 kByte boundary

Uwe Hermann uwe at hermann-uwe.de
Wed May 21 14:45:11 CEST 2008

On Wed, May 21, 2008 at 12:44:15PM +0200, llandre wrote:
> Why is the RAM physically unaccessible beyond 640 KByte at this stage? 

Which chipset / board? It's not necessarily unaccessible.

You have to be careful to not check the range from 640kb to 1MB,
after that it should be ok again.

E.g. try this if you have 64MB or RAM:

ram_check(0, 640 * 1024);
ram_check(1024 * 1024, 64 * 1024 * 1024);

If this does not work, then you likely have a RAM setup problem.
The fact that the 640kb-1mb range doesn't work with ram_check()
is sort of expected.

> Is it a specific (legacy) memory controller mode?

The northbridge / RAM controller has some registers which allow
you to control what happens with the accesses from 640KB to 1MB,
I think it depends on that config...

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