Low-power Linux server with an AMD Geode CPU

This page is about how to build a low-power server around an AMD Geode NX1750+ CPU using the Linux OS.
The most difficult part is to rebuild and configure the powernow-k7 kernel module. Once you have done that, your desktop system will have the same power but consumes considerably less power.

What motherboards will run the Geode?

• ASRock K7S41GX microATX form factor, onboard VGA, sound, LAN
• Abit KX7-333/KX7-333R ATX form factor, ATA RAID
• PC-CHIPS M811 (not tested by myself, but confirmed to work with the Geode NX1750+)

How to build the Linux system?

Right now, this is only a link section where the information can be found, which helped me to build a Linux server around a Geode-powered system.

• Dave Jones' Linux 2.6 K7 PowerNow! CPU frequency driver
• Adam Jones' K7 PowerNow! MSR Support page
• My modified powernow-k7.c for kernel 2.6.23 as suggested on Adam Jones' page.
• My modified powernow-k7.c for kernel 2.6.24 as suggested on Adam Jones' page.
• AMD Geode NX 1750 auf PC-Chips M811 als stromsparender VDR, German forum about the Geode NX1750+
• Athlon Powersaving HOWTO, enabling .
• AMD Geode NX datasheet
• powernowd

How to use the modified powernow-k7 module?

The modification adds the following parameters to the powernow-k7 module (table taken from Adam Jones' site)

Parameter	Description
overwrite_table	Set to non-zero to enable manual frequency table specification.
multiplier	Specifies an array of FSB multipliers, which must be multiplied by 10 (e.g. 8.5 -> 85, 10 -> 100).
voltage	Specifies an array of Vcore voltages corresponding to the given multipliers, in mV (e.g. 1125 -> 1.125V).
switch_latency	Set the settling time for CPU state transitions in microseconds. The default is 200us.

I found the following setting useful:
modprobe powernow-k7 overwrite_table=1 multiplier=30,60,75,90,105 voltage=1050,1050,1050,1250,1250 switch_latency=300
Although the voltage-setting is completely academic (I haven't found a desktop board yet that supports VID-switching), the switch latency setting is important. At 200us, I inevitably got lock-ups during FID-changes.

Questions, suggestions?