Develop Bugs

[Q] what exactly is undervolting

i have used the search and not found any solid info
what are the benefits of it if any

I haven't heard of people undervolting their fone, although i haven't looked to much.
This would mean though reducing the power that the CPU gets. I would imagine this increases battery life among other things.

Your right about what it is, but almost every custom rom/ kernel is undervolted in development section.
Sent from my HTC Desire using XDA App

Undervolting means, the CPU (or hardware in the phone) gets lower voltages, thus saving more battery & not loosing performance.
Undervolting is a process which reduces the excess "voltage" given to the CPU using a software. This is widely used as a cooling solution and in my opinion more effective than any other cooling solution available (thermal paste, cooling pad, etc) at NO cost. Undervolting will NOT compromise performance at all. Underclocking and Overclocking (clock speeds) is whats responsible in regards to performance. Benchmarks will also prove that performance remains the same.
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Not excess voltage but fully, manufacturer guaranteed, stable Core voltage to lower guesswork voltages which may or may not work and may or may not cause data loss/corruption.
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- Sent via HTC Desire -

A cpu needs power for every 'clock cycle'. 1Ghz means there are a billion per second. IF you lower the voltage, there is less power used. But if you lower it too much, the cpu wo'nt be able to 'cycle its clock'...
So undervolting doesn't affect performance, since the cpu remains on 1Ghz. It decreases the power used, so you get better battery life.
Every single cpu is different, so HTC has chosen a default voltage that (shoud) work on all phones they sell. But your particular cpu could be able to work at a lower voltage. It's just a matter of trail and error. Decrease the voltage until the cpu stops working, then higher it a bit. That way you've undervolted your cpu so it uses the least power.

koenvbeek said:
A cpu needs power for every 'clock cycle'. 1Ghz means there are a billion per second. IF you lower the voltage, there is less power used. But if you lower it too much, the cpu wo'nt be able to 'cycle its clock'...
So undervolting doesn't affect performance, since the cpu remains on 1Ghz. It decreases the power used, so you get better battery life.
Every single cpu is different, so HTC has chosen a default voltage that (shoud) work on all phones they sell. But your particular cpu could be able to work at a lower voltage. It's just a matter of trail and error. Decrease the voltage until the cpu stops working, then higher it a bit. That way you've undervolted your cpu so it uses the least power.
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Very sensible answer..Thanks

koenvbeek said:
A cpu needs power for every 'clock cycle'. 1Ghz means there are a billion per second. IF you lower the voltage, there is less power used. But if you lower it too much, the cpu wo'nt be able to 'cycle its clock'...
So undervolting doesn't affect performance, since the cpu remains on 1Ghz. It decreases the power used, so you get better battery life.
Every single cpu is different, so HTC has chosen a default voltage that (shoud) work on all phones they sell. But your particular cpu could be able to work at a lower voltage. It's just a matter of trail and error. Decrease the voltage until the cpu stops working, then higher it a bit. That way you've undervolted your cpu so it uses the least power.
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How would one go about under volting .i have tried everything suggested to me and nothing really seems to make a difference
Sent from my HTC Desire using XDA App

Most kernels are undervolted and unless you can compile the kernel for yourself you are stuck with the values given by the creator. There are two exceptions for this, HAVS kernels which automaticly chose a voltage depending on temperature and some other stuff and SVS kernels with snq-'s volt selection interface (found in Leedroid and maybe some other kernels/roms).
So what exactly have you tried and what did you expect to see? Because the difference won't be that noticeable.

TheGhost1233 said:
Most kernels are undervolted and unless you can compile the kernel for yourself you are stuck with the values given by the creator. There are two exceptions for this, HAVS kernels which automaticly chose a voltage depending on temperature and some other stuff and SVS kernels with snq-'s volt selection interface (found in Leedroid and maybe some other kernels/roms).
So what exactly have you tried and what did you expect to see? Because the difference won't be that noticeable.
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I have tried battery calibration, using app watch dog to let me know which apps are using excessive CPU. Putting my brightness down to 10%, making sure not everything is synced, the only thing synced is beautiful widgets every 4 hours. And just about everything else that has been put forward to me. Here's another example I just taken my phone off charge at 100% and wrote this and I'm now at 73 %. And its only taken2 mins to write
Sent from my HTC Desire using XDA App

adz63 said:
I have tried battery calibration, using app watch dog to let me know which apps are using excessive CPU. Putting my brightness down to 10%, making sure not everything is synced, the only thing synced is beautiful widgets every 4 hours. And just about everything else that has been put forward to me. Here's another example I just taken my phone off charge at 100% and wrote this and I'm now at 73 %.
Sent from my HTC Desire using XDA App
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So in short you havent tried any kernel with undervolting at all!

Well that all has nothing to do with undervolting, but (extra) undervolting will not fix the drain problem you have.
Do you use setCPU cause your sig says you run at 1113MHz, which cause higher consumption. Also did you set your wifi sleep policy to never(setting-wireless and network-wifi settings-press menu-advanced-wifi sleep police).

At the moment I have the havs kernel that comes with oxygen 2.0 rc6. I have posted another topic about is the kendal good for battery life etc and no1 has told that another kendal would make anything better
Sent from my HTC Desire using XDA App

TheGhost1233 said:
Well that all has nothing to do with undervolting, but (extra) undervolting will not fix the drain problem you have.
Do you use setCPU cause your sig says you run at 1113MHz, which cause higher consumption. Also did you set your wifi sleep policy to never(setting-wireless and network-wifi settings-press menu-advanced-wifi sleep police).
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@TheGhost1233, how exactly does one decide which kernel suits us best..
Eg: I see two undervolted kernels (I think) at 875 and 925 mV. I have no idea how to decide. Trial and error?
Froyo Kernel [email protected] min
Froyo Kernel [email protected] min

@droidzone Yes trial and error. The mentioned voltage is the lowest the cpu will get at 245MHz. Not all devices are stable with 875mV (you will know if your phone freezes up) so then you move up to the 925mV min. Other than the voltage there is no difference between 875mV or 925mV.
With the HAVS kernels it can take a while before you notice the freezes cause the voltage is dynamic, so be careful if you need your phone as a alarm clock.

[Q] Same voltage = Same battery drain?

Hello!
I recently noticed how frequencies 122MHz through 460MHz all employ the same voltage (900mV). I've come to understand that the higher the CPU frequency the faster your battery will drain. What I don't understand is why a higher frequency will drain your battery faster.
Is the only cause for higher battery drain when running a higher frequency, the higher voltage which comes with a higher frequency, or are there other factors?
If, then, a higher voltage is the only cause, then my battery would not drain faster if I clocked my minimum frequency at 460MHz instead of 122Mhz?
Thanks in advance to anyone who can shed some light on this!

Hi
cpu power consumption at a specific frequency is bound to its voltage.
you should test a voltage for a frequency while your device has 100% workload, because you could find a voltage so that your device is stable while being idle, but freezes when it needs to work. (for more information search for linux phc)
my conclusion:
the voltage for a specific frequency has minimum!
you can set your minimum frequency to 460 if you want to, since the screen consumes most power, it should not matter that much. i have set my minimum freq that high, too. I believe that way, my phone needn't raise the frequency when dooing simple stuff, like playing music.... but i am just guessing.
i theory it must get hotter than at lower frequencys, but i did not notice that.
i have had a palm pre and a custom kernel introduced a voltage on demand governor, which kept the device at 1ghz all the time, but changes the voltage with the workload. i think the developer of the awesome idea is "unixpsycho" ... i would like to see something similar on android.
greetings
matto
EDIT:
http://en.wikipedia.org/wiki/Dynamic_frequency_scaling
it looks like it is bound to the frequency, too!
~const*f*V^2
the Voltage is quadratic, that means it tkes a higher priorety.
e.g. lowering the voltage from 900mv to 800mv => (0.8^2)/(0.9^2) ~ 0.79
460mhz*0.79~363mhz
=> [email protected] consumes as much power as [email protected] (Stock)

Can anyone tell me about cpu governers and what they actually mean! !thanks !

Sent from my GT-S5360 using Tapatalk

Governors regulate the performance of the cpu. You can use it/customize it to fit ur needs.
For detailed info look here:http://forum.xda-developers.com/showthread.php?t=1369817

correct name is CPUfreq governors. and it's not about performance, it's about power saving. basic idea is put your cpu clock in lower clock while not busy. in digital circuit lowering working frequency (clock) also make power consumption lower. for reference check link provided by hell_lock. unfortunately on our device it's effect is small because different between lower and higher freq is small (312MHz to 832Mhz), and freq scaling latency is relative high.

CPU voltage power usage

Quick questions:
1) Is power usage by the CPU DIRECTLY affected by voltage? For example, does 1V use twice the power of 0.5V? ...or is it not a linear response like that?
2) Does the frequency (at same voltage) influence power usage by the CPU? Ex. 1.0GHz vs 1.1GHz, both at 1V.
Sent from my LG-P930 using Tapatalk 2

yes no

Flyview said:
1) Is power usage by the CPU DIRECTLY affected by voltage? For example, does 1V use twice the power of 0.5V? ...or is it not a linear response like that?
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Yes, it's linear. The formula is P=I*V where P is power, I is current, and V is voltage.
2) Does the frequency (at same voltage) influence power usage by the CPU? Ex. 1.0GHz vs 1.1GHz, both at 1V.
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Yes, definitely, because when running at a higher frequency, the CPU will be drawing more current (see above formula). That's the whole reason that CPUs will slow themselves down when not needed.

drumist said:
That's the whole reason that CPUs will slow themselves down when not needed.
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When idle, CPU's slow down not only frequency but voltage too. Thats why cpu's consume less energy on lower frequencies. Processor on the same volgate, but different frequencies consumes almost the same power.

-ReaL- said:
When idle, CPU's slow down not only frequency but voltage too. Thats why cpu's consume less energy on lower frequencies. Processor on the same volgate, but different frequencies consumes almost the same power.
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Dynamic power consumption is directly (linearly) affected by frequency, but static (leakage) power consumption is a different beast. I may be overestimating how big the dynamic power consumption is in comparison to static with these tiny SoCs.

drumist said:
Yes, it's linear. The formula is P=I*V where P is power, I is current, and V is voltage.
Yes, definitely, because when running at a higher frequency, the CPU will be drawing more current (see above formula). That's the whole reason that CPUs will slow themselves down when not needed.
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Yes, that's what I'm wondering. Is the voltage and current increased with higher frequency or just voltage? If just voltage then the power use of any two frequencies at the same voltage is the same. If current also changes based on frequency, then two frequencies at the same voltage would use a different amount of power.
Sent from my LG-P930 using Tapatalk 2

Flyview said:
Yes, that's what I'm wondering. Is the voltage and current increased with higher frequency or just voltage? If just voltage then the power use of any two frequencies at the same voltage is the same. If current also changes based on frequency, then two frequencies at the same voltage would use a different amount of power.
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No, current increases with frequency. But there is also a certain amount of power that is consumed no matter what the frequency is (so having a very low frequency doesn't mean it's consuming almost no power -- it just means it's consuming LESS power). I'm kind of oversimplifying it in my last post. It's complicated stuff, and I don't claim to be an expert at it. I'm just an amateur.
---------- Post added at 02:54 PM ---------- Previous post was at 02:13 PM ----------
I've been researching this a little bit since I have some free time and it caught my interest. Here's what I've come up with:
P ≈ k₁·V²·f + k₂·V
k₁ and k₂ are constants. (They have meaning but it's not necessary that we understand them.) V is voltage, and f is frequency. The first term (k₁·V²·f) is dynamic power, and the second term (k₂·V) is static or leakage power.
Some things to take away from this is that power consumption is more than halved when the voltage is halved. Even though it would appear that reducing the frequency only influences the dynamic power, the CPU automatically scales the voltage down when the frequency is lower, so as a chain reaction, the static power is also reduced significantly. (And as it happens, the static power is larger than dynamic power with modern chips, so that's important.)
Again, I'm not an expert on this. If someone sees an error or misunderstanding let me know.

Where is current in your formula? I know the CPU has voltages you can set for each frequency, what you would call the static voltage, but what is this dynamic power? Let's say I run the phone at 1.51Ghz at 1087.5mV. Would it consume more power than running at 1.35Ghz, if also set at 1087.5mV?
Sent from my LG-P930 using Tapatalk 2

Flyview said:
Where is current in your formula? I know the CPU has voltages you can set for each frequency, what you would call the static voltage, but what is this dynamic power? Let's say I run the phone at 1.51Ghz at 1087.5mV. Would it consume more power than running at 1.35Ghz, if also set at 1087.5mV?
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The current is incorporated in the frequency term. The reason the dynamic power term has frequency in it is because the current drawn is proportional to the frequency. Basically, current equals frequency times a constant, which was absorbed into k₁.
Yes to your last question, but it may not be a huge difference.

[Q] something about lowering the voltage

Lowering the coltage can help with heat and battery.I flashed the ElementalX kernel,but flar2 didn't tell much about lowering the voltage.
My PVS number is 3,so how much voltage should be lowerd?Not only the minimum,but also others.
I may lower it too much(-100mv),then I got a reboot while playing videos.
Thank you

a1317931279 said:
Lowering the coltage can help with heat and battery.I flashed the ElementalX kernel,but flar2 didn't tell much about lowering the voltage.
My PVS number is 3,so how much voltage should be lowerd?Not only the minimum,but also others.
I may lower it too much(-100mv),then I got a reboot while playing videos.
Thank you
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Check this guide
http://forum.xda-developers.com/showthread.php?t=2469261

a1317931279 said:
Lowering the coltage can help with heat and battery.I flashed the ElementalX kernel,but flar2 didn't tell much about lowering the voltage.
My PVS number is 3,so how much voltage should be lowerd?Not only the minimum,but also others.
I may lower it too much(-100mv),then I got a reboot while playing videos.
Thank you
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Overclocking will effect the heat too. The Voltage can be adjusted but most of the time don't need to be fooled with.
Sent from my Nexus 7 Flo running CM 11 4.4.2 with ElementalX Kernel using XDA Premium 4 mobile app

There is very little effect on battery by lowering the CPU voltage. There is a thread somewhere here on XDA where they do out the math and the energy savings from reducing CPU voltage are like 1% or something super low like that. The CPU uses very little power when you compare it to everything else in the tablet, like the 1080p screen, wireless, etc etc etc. Additionally, the overall power used by the CPU is based on both the clock speed and voltage, with high clock speeds being the major contributor to power consumption. Using a power scheme which does not ramp the CPU frequency as quickly or even underclocking the cpu will yield much greater power savings and heat reduction than voltage reduction ever will.

Hnk1 said:
Check this guide
http://forum.xda-developers.com/showthread.php?t=2469261
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well,I mean,the volatage of CPU,not the battery...
anyway,thank you

LinearEquation said:
Overclocking will effect the heat too. The Voltage can be adjusted but most of the time don't need to be fooled with.
Sent from my Nexus 7 Flo running CM 11 4.4.2 with ElementalX Kernel using XDA Premium 4 mobile app
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I just use the stock frequency.I like reading,high performance isn't needed,so I just want to increase some battery life,some people in tieba told me that lowering cpu voltage can make some great help...

skrypj said:
There is very little effect on battery by lowering the CPU voltage. There is a thread somewhere here on XDA where they do out the math and the energy savings from reducing CPU voltage are like 1% or something super low like that. The CPU uses very little power when you compare it to everything else in the tablet, like the 1080p screen, wireless, etc etc etc. Additionally, the overall power used by the CPU is based on both the clock speed and voltage, with high clock speeds being the major contributor to power consumption. Using a power scheme which does not ramp the CPU frequency as quickly or even underclocking the cpu will yield much greater power savings and heat reduction than voltage reduction ever will.
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oh,it make sense,some people in tieba told me that lowering cpu voltage can make some great help with heat and battry life,look like they misled me,I have nerver noticed the diffrences in heat and battery, only the unstability is obvious...
thank you

skrypj said:
There is very little effect on battery by lowering the CPU voltage. There is a thread somewhere here on XDA where they do out the math and the energy savings from reducing CPU voltage are like 1% or something super low like that. The CPU uses very little power when you compare it to everything else in the tablet, like the 1080p screen, wireless, etc etc etc. Additionally, the overall power used by the CPU is based on both the clock speed and voltage, with high clock speeds being the major contributor to power consumption. Using a power scheme which does not ramp the CPU frequency as quickly or even underclocking the cpu will yield much greater power savings and heat reduction than voltage reduction ever will.
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Especially with all things considered, the CPU is mostly loafing along. It doesn't start drawing power until it's being asked to work. Lowering the voltage is asking for a laggy device when the chips are down.

I highly suggest lowering the Cpu clock speeds if you want to affect the heat and battery. Lowering the cap speed for the device doesn't allow it to work hard enough to reach speeds to really make it toasty. Same goes with battery life. For example, I'm sure that you can walk much farther than you can run.
Changing the voltage is the equivalent of running down a new street...you have to test and test before you find a good voltage. Every device is different. Someone else's device might do great with the exact same settings that are making your device reboot. Do a lot of reading if you are certain that you want to change the voltages.