It seems that, although it's simple in Windows w/ Afterburner, you cannot UNDERVOLT under BAMT/Linux. I mean you can, but it's not applied, even if it's reported as applied, neither with atitweak, neither with cgminer.
I mean you can undervolt, but it's useless because there are some frequency thresholds and if you set frequency greater than threshold for a voltage, voltage automatically goes to the next respective voltage. The thresholds are:
0.85V -> 450MHz
0.90V -> 600MHz
0.95V -> 700MHz
nominal voltage -> unlimited frequency to at least 1210MHz (I could not try more).
I'm pretty sure about this behavious, I have tested with both GPU-Z under Windows, and voltmeter on GPU voltage rail and clampmeter on video card power supply wires under Linux.
To add insult to injury, you cannot modify the BIOS, it seems there's a checksum nobody knows how to compute.
Now, why I would want to undervolt? Lets say I'm able to undervolt 10%. I'll loose around 10% maximum frequency (hashing rate). But I'll made around 30% power savings (21% from voltage drop, 10% from frequency). So, with only 10% lower hashing rate, 30% power savings, and much lower noise.
But there might be a way. It looks like 7970 nominal voltage can be one of the following:
1.175V = ASIQ quality <75
1.112V = ASIQ quality between 75 and 80
1.050V = ASIQ quality between 80 and 85
1.025V = ASIQ quality between 85 and 90
So, in theory, if you write a 1.025V BIOS on a 1.112V card and it works, like I want to do, you'll make a 8% undervolt.
Can somebody help me with a 1.025V BIOS for MSI R7970-2PMD3GD5?
(on
www.techpowerup.com there's only one BIOS for my card
)
In Windows, ASIC quality can be obtained with right click on GPU-Z title bar. BIOS can be dumped from GPU-Z also.
