[coreboot] How to test RAM beyond 640 kByte boundary

Marc Jones Marc.Jones at amd.com
Wed May 21 18:08:20 CEST 2008

llandre wrote:
>>>> Why is the RAM physically unaccessible beyond 640 KByte at this stage? 
>>> Which chipset / board? It's not necessarily unaccessible.
>> AMD Geode LX/CS5536
> I forgot to mention that is a custom board.

The 640-1MB area is covered by a basemask descriptor (A0000-BFFFFh) 
setup and used by graphics and a swisscheese descriptor (C0000h-FFFFFh) 
for the legacy shadow memory hole. In 
northbridge/amd/lx/northbridgeinit.c see the gliutables structures.

In both tables you could change the swisscheese to allow reads and 
writes to memory like this:

{.desc_name = MSR_GLIU0_SHADOW,.desc_type = SC_SHADOW,.hi = MSR_MC + 
0xFFFF,.lo = 0xFFFF0003},


Marc Jones
Senior Firmware Engineer
(970) 226-9684 Office
mailto:Marc.Jones at amd.com

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