Arch Linux

rowhammer

Member

Registered: 2019-12-05

Posts: 16

[Solved] Can't read voltage with lm_sensors

I am trying to read the CPU voltage on a Ryzen 3700X chip installed in an ASRock 470M Pro motherboard. I just built this computer and saw a steady CPU voltage of 1.472 in the BIOS, which seemed too high, and I wanted to check it with Linux running while idle. (The BIOS hammers one CPU core at full blast with a wait loop for user input.)

I ran sensor-detect, agreeing to all probes, and then sensors. I see 15 voltage measurements labeled from in0 to in14. The in0 measurement has (min = +0 V, max = +1.74 V) after it; all others have 0 for both values. Based on comparing this to VCORE readouts on other computers (for example: https://serverfault.com/questions/37975 … ge-alarms), and the fact that in0 is the only measurement that fluctuates with CPU usage, I'm guessing this is the CPU voltage.

However, something is wrong with this value. At idle, I get at lowest 96 mv. With the stress utility, 16 cpu workers, running for a few minutes, I get at most about 680 mv. AMD suggests the chip as a normal operating range of .2 to 1.5 V, so these can't be right. (Reference: https://www.reddit.com/r/Amd/comments/c … gen_ryzen/.)

One thought I had is that this reading is off by a factor of 2. This would give a range of about .2 to 1.4 V, which seems better. Is this known behavior?

(Of course, that doesn't explain what's going on in the BIOS, but since I'm rarely there I suppose the high voltages won't cause too much CPU wear. I'm mostly concerned about normal operating conditions, so if my hunch above is correct, I'm happy.)

I'm running a fresh Arch install, fully up to date, and I'm happy to provide any additional information. Thank you!

Last edited by rowhammer (2019-12-07 22:30:05)

Zod

Member

From: Hoosiertucky

Registered: 2019-03-10

Posts: 636

Re: [Solved] Can't read voltage with lm_sensors

https://hwmon.wiki.kernel.org/voltagelabelsandscaling

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rowhammer

Member

Registered: 2019-12-05

Posts: 16

Re: [Solved] Can't read voltage with lm_sensors

Thank you for the link. It notes that in0 should be the CPU voltage, and that it should be unscaled. I agree with the first part, but I find the second claim very odd. It would mean my CPU draws only .1 V at idle, at no more than .7 V under a full stress test. This cannot possibly be correct.

rowhammer

Member

Registered: 2019-12-05

Posts: 16

Re: [Solved] Can't read voltage with lm_sensors

Checking various config files in the lm_sensors package for other ASRock motherboards reveals that the reading is indeed off by a factor of two.