[coreboot] How to test RAM beyond 640 kByte boundary

llandre r&d2 at dave-tech.it
Wed May 21 15:41:38 CEST 2008

>> Why is the RAM physically unaccessible beyond 640 KByte at this stage? 
> Which chipset / board? It's not necessarily unaccessible.
AMD Geode LX/CS5536

> 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);
I see.

> 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...
I'll have a look at datasheet.

Thank you very much,

DAVE Electronics System House - R&D Department
web:   http://www.dave.eu
email: r&d2 at dave-tech.it

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