On Sun, Apr 21, 2013 at 5:43 AM, Rudolf Marek <r.marek@assembler.cz> wrote:

In the long term, would it be possible to do this stuff from the OS,
not some bios setup screen? Or is it too late by the time the OS is
booted? On the SiS 630 we controlled overclocking parameters via a
user mode command once Linux had booted, but that was long ago ... do
the new chips make this easier, or harder?

Yes sounds like good idea (to have it in nvram) but only as option. My DDR3 memory does not work well on 1.5V (it has to have 1.65V) from the start.

The memory voltage can be automatically detected from the SPD - http://www.coreboot.org/Developer_Manual/RAM_init

The SPD logic is in AGESA, I don't know exactly how to get the voltage parameters out of it, but AGESA does not change the voltage, it just uses SPD to set the timings.

Configuring the voltage in nvram would still be useful if the user is undervolting to save power or maybe overclocking in the future.

David