Internal PLL overvoltage?

[Yuriman]

What exactly is Internal PLL overvoltage? Google-fu reveals a lot of people saying "I have no idea what it does but I need it for 4.5ghz+ on Ivy". What exactly does it do? What does it affect? How dangerous/harmful is it, will it have an adverse effect on temperatures?

Also, I read that on Ivy, you can't use offset voltage mode with C-states, it must be one or the other. Which one gives lower typical power usage?

 

[Kenmitch]

Not a whole lotta info out there on it....The following seems kinda believable tho.

CPU PLL Voltage Override (Overvoltage): What the Heck does it do?
So I asked that question to an Intel Overclocking Engineer his explanation was roughly: We went through the BIOS settings trying to find setting that if changed could help overclock our CPUs further. We came across this setting. Think of the CPU PLL voltage as a voltage that is provided to the CPU, but then “clipped” down to an approximate voltage. No matter what that input is whether 1.3v or 1.9v it is clipped (hypothetically let’s say 800mv after clipping (he didn’t say how much)) that way other devices can use the PLL voltage and clip to what they need. The CPU PLL Overvoltage allows for less clipping of that voltage. It can also reduce the lifespan of the CPU, but nothing noticeable.

It's one of those things that you need it enabled or you don't tho. On my 2550k I have it disabled and I'm at 4.8ghz without issue. I'd have to double check but I think it's disabled still in my 5ghz profile also.

Using offset vcore voltage with c-states enabled/disabled would be a YMMV dependant on your cpu. Try running with them enabled to see if your still stable. If you have no issues then keep them enabled. If you run into random bsods doing single core loaded things such as web surfing, email, etc then you might have to disable some. I'm playing around with the C3 and C6 states disabled as it allows me to run with lower overall vcore. With these disabled I still get low voltage at idle and the vcore I need at load. Pretty much just nukes the lower 1 core, 2 core vcore that the chips will ask for.

 

[Haserath]

^Makes sense. I tried googling some Intel docs, but the best I found basically said.

Disable: keeps default "internal pll" voltage.
Enable: Increases voltage to the internal pll. This may help at extreme processor frequencies.

It also had a note that ACPI S3 state couldn't be used if it was enabled. So basically sleeping the processor is a no go with internal pll overvoltage enabled.

If you want to use less energy, leave it disabled. It may or may not improve an overclock's stability, it probably depends on the chip.

 

[Soulkeeper]

from what little i've been able to gather on PLL it seems to be related to pcie, hdmi/dp, and possibly the connection to the motherboard chipset. I've seen it labeled as "Display PLL" and more ... depending on the cpu/chipset in question.

"Short for phase-locked loop, an electronic circuit that controls an oscillator so that it maintains a constant phase angle (i.e., lock) on the frequency of an input, or reference, signal. A PLL ensures that a communication signal is locked on a specific frequency and can also be used to generate, modulate and demodulate a signal and divide a frequency. "
http://www.webopedia.com/TERM/P/PLL.html

another interesting read

After reading this it appears that increasing the reference clock could potentially put more stress on the PLL components requiring more voltage to stabilize or reduce jitter. potentially increasing clock/system stability. I think needing more voltage is likely a fringe case (extreme bclk overclock), to be used sparingly.

 

[borisvodofsky]

First off.

Internal PLL over-voltage is DIFFERENT from cpu pll voltage.

You usually can only adjust cpu pll voltage.


cpu pll voltage should be from 1.60 to 1.8125, this range has been tested, where the lower voltages have allowed some overclockers to use LOWER total vcore for a certain overclock. :biggrin:

Internal PLL over-voltage is only to hold HIGH multipliers 48+ :twisted: