# Kaby Lake undervolting

## Maxie

Hello,

I read that PHC doesn't work with Skylake and Kaby Lake. Is there another method to undervolt the CPU? I've read something about MSRs, but:

1. It's quite scary, quite error prone and error can be costly

2. I actually looked into Intel's MSR docs and didn't find voltage offset or anything voltage related really

3. I haven't found any information on interaction with intel pstate driver, I don't know if the chipset (h170) may lock voltage control (like it locks overclocking), etc.

4. I'd like to know before I buy, so I can't experiment....

Any suggestions?

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## Roman_Gruber

does afaik only worked with core2duo (penryn). ivybridge also nope.

I assume a desctop mainboard has some options. notebooks definitely nope. except a few notebooks with special bios like from clevo, alienware ... 

I suggest you go the BIOS route.

I wanted to reverse engineer my mainboard, but nope, the datasheets for the important ICs are not available! Especially when you read libreboot you will see a bit more a rant... All closed source. when you do not even find a pinout for some "management" ICs for the mainboard, it is a very very sad story.

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## szatox

Yup, tweaking setting in bios is going to be the most reliable way. The obvious downside is you have to reboot every time you change something, and changing by small factors will require many iterations. On the other hand you want to run some stability tests every time you change something, so the time spent rebooting may be insignificant.

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## Maxie

Clevo W650KK1. This is not an overclocking model and a reseller told me there's no undervolting in BIOS.

So even MSR writes won't work? They normally do on Windows, f.e. that's how Throttlestop works.

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## Roman_Gruber

well with clevo you are lucky. Usually all moders use clevo. You have to ask those special sites for a modded bios. We are here not a point for htat.

for myself I could use an overclocker gpu bios, but I do not want to brick my box. It is a bit too risky, fishy to flash an unkown bios. my bios chip is soldered, so replacing is a pain. 

Second my bios contains some special data, so when that chip gets "destroyed" i will have some issues. Please research it yourself why I wrote that statement. 

Only safe route is to have some "bus pirate" or whatever you want to call it, to read out the chip full before, and than flash, when something goes wrong, flash back. but that implies you know how the board works, and if its technically possible, and if its risk free.

Laptops Sucks in this regard.

--

regarding your statement.

i tried to reserearch it for different models myself for different cpus. it is not that easy. some important docs are just missing. I suspect intel does not want them out of the hands.

when you know how it works, you can tweak it or try to tweak it.

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## Maxie

 *Roman_Gruber wrote:*   

> well with clevo you are lucky. Usually all moders use clevo. You have to ask those special sites for a modded bios. We are here not a point for htat.
> 
> for myself I could use an overclocker gpu bios, but I do not want to brick my box. It is a bit too risky, fishy to flash an unkown bios. my bios chip is soldered, so replacing is a pain. 
> 
> Second my bios contains some special data, so when that chip gets "destroyed" i will have some issues. Please research it yourself why I wrote that statement. 
> ...

 

Thanks for the answer.

Really, I hoped it would be possible w/out a BIOS mod (especially that I haven't found any for this board), but at least I have a pointer to the next place to ask.

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