Question Undervolting an Athlon II (K10h) ?

[Alexey260]

Hello, everyone. I decided to give a second life to my old PC (Athlon II x2 260 (3.2GHz) + Biostar A780L3L) and started with undervolting the CPU for lower power consumption. I'm on Linux (Debian 12) and so using the k10ctl software.

I can't decide, which one is real voltage. Bios shows that voltage is about 1.4 V. When stress-testing with mprime lm-sensors shows 1.42 V (if i chose the right voltage, "in2" was the only reacting at CPU being loaded/idle), when idle 1.14 V.

But k10ctl shows max voltage at P-State 0 as 1.25 V. And 0.7375 V when idling (P-State 3).
I managed to drop P-0 voltage to 1.19 V (lm-sensors) = 0.8 V (K10Ctl) and running mprime for 10 minutes with no errors or hangs (will try it run longer next time and also try lowering voltage more)

So, which voltage is true, and why is there such a difference between BIOS and K10ctl ?
Any chance to have same values in both? With BIOS one i went from 1.42 V to 1.19 V (x0.838). With K10ctl i went from 1.25 V to 0.8 V (x0.64). I have this PC plugged into smart socket, and watching total power consumed. From 112 W i came to 77.3 W (x0.69) which is closer to K10ctl voltage decrease.

 

[Alexey260]

Found the answer. Motherboard has single power phase for both CPU and northbridge (or something like that), so it allows changing the voltages only for both of them at a time, not separately. That also explains why when i removed undervolt for NB, the PC power consumed and CPU reported voltage were the same as default, even if CPU voltage set in K10ctrl was like 0.64 from base.

 

[Alexey260]

Also, despite k10ctl showing VID interface as parallel, according to real voltages and the calculations it is serial, which make voltages realistic 1.10-1.16 instead of 0.8