# Franco Kernel - Undervolt results



## Genia4 (Nov 11, 2012)

Hey
I have been lurking for quite a bit, so although this is my first post, I'm not new to the Galaxy Nexus' internals.

For the past few months, I have been using Imoseyon's excellent Lean Kernel (latest 180mhz exp build) and have been trying out various modifications on my device. One topic which interests me is consistent undervolting. Recently I've switches to franco's kernel (latest version, 512mhz GPU) due to the much larger number of frequency steps.

From TI's OMAP4460 documentation we learn a few things:
The MPU's nominal voltage is 1.35v, 1350mv as seen on most undervolting apps.
The OMAP4460 comes in two flavors - 1200mhz and 1500mhz. This is the frequency for which the above voltage applies. The Galaxy Nexus uses the 1200mhz variant.
From the specs, the controllable voltage regulators can have a variation of up to 50mv.
The maximum voltage the MPU will take is 1500mv. I could not find whether this number applies to sustained voltage or to a short peak.

The Galaxy Nexus' stock voltages are:
350mhz - 1025mv
700mhz - 1203mv
920mhz - 1317mv
1200mhz - 1380mv

On my device, for every frequency franco's kernel offers, I went down to the lowest 10mv step where the device transitioned from stable to unstable. Stability testing was done by running both SetCPU and another app called Stability Test for at least 15 minutes at the undervolted frequency.

My current results are:

1305mhz - 1160v (1150mv freezes)
1228mhz - 1120v (1110mv reboots)
1036mhz - 1050v (1040mv reboots)
729mhz - 910v (900mv reboots)
537mhz - 820v (810mv soft reboots)
384mhz - 740v (730mv reboots)
192mhz - 660v (650mv freezes)
During daily use, I add 60mv to each of the above values and I experience no reboots,freezes or any instability whatsoever. Those 60mv should account for temperature variation, as well as voltage regulator variation.

TI's docs also mention that for a certain frequency, different silicone profiles can account for up to 20% change in the needed voltage. So, as always, YMMV.

Now, I wouldn't recommend running the above very aggressive undervolt for a usable device, as a change in temperature could render the phone unstable. What the above numbers are useful for is seeing the relationship between the various frequencies and their respective stable voltage.
How much battery savings can be achieved? Probably not much, as the values aren't that far from stock. The thing that undervolting can help with is mainly temperature. You could run either a higher frequency at the same temperature as a lower one, or just lower the overall temperature of your device. My phone, with default settings starts throttling after the MPU stays at 1200mhz or more for more than a few minutes under stock settings.

I hope this helps anyone.

Disclaimer:
Don't do anything stupid and then blame me. Actually, don't do anything stupid at all. Running the device above 1350mv for any length of time might shorten its lifespan. 1500mv, although a maximum in the docs, should not be approached.


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## EniGmA1987 (Sep 5, 2011)

For me if I go down to the voltages you list +40mv, as soon as I hit apply the phone crashes. Smart Reflex is turned off of course when I try to set them this low. I am also on Popcorn Kernel and not Franco


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## hlaalu (Jul 13, 2012)

really neat, thanks for the info. your disclaimer says running anything over 1350mv is bad, but the stock is 1380mv. I'm a little confused by that, thanks!


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## erock91 (Mar 21, 2012)

I always have issues with losing my data connection when i undervolt too much.. Everything else stays stable but ill have to reboot two or three times a day due signal loss..


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## EniGmA1987 (Sep 5, 2011)

erock91 said:


> From the specs, the controllable voltage regulators can have a variation of up to 50mv.


Are you sure this is the voltage steps with each frequency? Or is this the actual voltage regulators? I dont know if you noticed, but Franco actually undervolts some of the regulators, not just frequency slots.


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## erockk13 (Sep 14, 2012)

EniGmA1987 said:


> I have seen this myself too, but only when underclocking certain things. Like specific voltage regulators. Cant remember the name of which one it was though.
> 
> Are you sure this is the voltage steps with each frequency? Or is this the actual voltage regulators? I dont know if you noticed, but Franco actually undervolts some of the regulators, not just frequency slots.


How do you go about doing that? I didn't even know choosing regulators was possible..

Sent from my Galaxy Nexus using RootzWiki


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