[coreboot] BIOS RAM in AMD SB7XX southbridges ?

Carl-Daniel Hailfinger c-d.hailfinger.devel.2006 at gmx.net
Wed Oct 28 00:51:42 CET 2009

On 27.10.2009 21:51, David Hendricks wrote:
> On Tue, Oct 27, 2009 at 6:06 AM, Darmawan Salihun wrote
>> What is the BIOS RAM in AMD SB7XX used for?
> Looks like scratchpad memory to me. From the public
> doc<http://developer.amd.com/assets/43366_sb7xx_bdg_pub_1.00.pdf>
> :
> 3.3 BIOS RAM
> The SB700 has 256 bytes of BIOS RAM. Data in this RAM is preserved until
> RSMRST# or S5 is
> asserted, or until power is lost.
> This RAM is accessed using index and data registers at CD4h/CD5h.
> Might it be enough to act as a very, very small cache-as-RAM substitute
> until CAR can be set up?

Given that it is not memory mapped and needs indexed access, it is
unusable for cache-as-RAM (unless you just want to outsource some
storage manually). Since CAR works fine on all AMD processors, the point
is moot anyway.
It would serve nicely as persistent storage for S3, though.


Developer quote of the week: 
"We are juggling too many chainsaws and flaming arrows and tigers."

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