NexusHD2 Android Forum

How to tweak CPU voltages? And I think that even with the same voltage, lower speed should consume less electricity. Is that right or wrong?

marco.palumbi wrote:
Power consumption in a CMOS device is proportional to the frequency at wich it operates.
power consumption also goes with the sqare of voltage.
so reducing the voltage is more effective than reducing the clock speed, nevertheless reducing the clock speed reduces the power consumption.

Can you expand upon that a bit. It is my understanding that the HD2 is not a CMOS device, per se, but it does have related sensors (camera, etc.). Remember we are talking solely about the HD2's CPU.

I do not know about you, but I have my device doing things while the screen is off, and if the CPU frequency is too low, the HD2 might crash, boot-loop, display does not restore, etc. Increasing the CPU frequency without changing the voltage is a safe correction that has worked for me. Could be that the lower CPU frequencies are associated to the same voltages for this very reason. I do not know.

My only experimentation in changing the voltage values was making use of Tyween's settings, which have always worked great, if you are familiar with TyphooN ROMs.

Please note that I do not know any of this as fact. I do not think an intelligent person would place him/herself in the crosshairs by doing so.

I have not looked at The Electronics Handbook in sometime, but I do not recall smartphones' CPUs being addressed there.

My post was more of a "huh!", why all the chatter about being concerned about the lower CPU frequencies if they are defaulting to the same voltage.

Play a bit, after doing a complete backup, and check your mileage.

MarkAtHome wrote:Can you expand upon that a bit. It is my understanding that the HD2 is not a CMOS device, per se, but it does have related sensors (camera, etc.). Remember we are talking solely about the HD2's CPU.

I do not know about you, but I have my device doing things while the screen is off, and if the CPU frequency is too low, the HD2 might crash, boot-loop, display does not restore, etc. Increasing the CPU frequency without changing the voltage is a safe correction that has worked for me. Could be that the lower CPU frequencies are associated to the same voltages for this very reason. I do not know.

My only experimentation in changing the voltage values was making use of Tyween's settings, which have always worked great, if you are familiar with TyphooN ROMs.

Please note that I do not know any of this as fact. I do not think an intelligent person would place him/herself in the crosshairs by doing so.

I have not looked at The Electronics Handbook in sometime, but I do not recall smartphones' CPUs being addressed there.

My post was more of a "huh!", why all the chatter about being concerned about the lower CPU frequencies if they are defaulting to the same voltage.

Play a bit, after doing a complete backup, and check your mileage.

Hi Mark,

honestly I don't know about any other manufacturing technology than CMOS used for commercial CPUs and SOCs.
Qualcomm Snapdragon QSD8250 should be a 65 nm device: http://en.wikipedia.org/wiki/65_nanometer

Said that, the aim of my post wasn't to focus on which frequencies/voltages functions or are the best for this device.
I would focus on the fact that lowering the CPU speed without lowering the voltage, the power consuption decreases.
this for the way the CMOS technology works. https://en.wikipedia.org/wiki/CMOS#Powe ... nd_leakage
So, generally speaking, it is not completely needless to lower the clock speed without lowering the voltage from the power consuption point of view...

hope this clarifies my post.

marco.palumbi wrote:Hi Mark,

honestly I don't know about any other manufacturing technology than CMOS used for commercial CPUs and SOCs.
Qualcomm Snapdragon QSD8250 should be a 65 nm device: http://en.wikipedia.org/wiki/65_nanometer

Said that, the aim of my post wasn't to focus on which frequencies/voltages functions or are the best for this device.
I would focus on the fact that lowering the CPU speed without lowering the voltage, the power consuption decreases.
this for the way the CMOS technology works. https://en.wikipedia.org/wiki/CMOS#Powe ... nd_leakage
So, generally speaking, it is not completely needless to lower the clock speed without lowering the voltage from the power consuption point of view...

hope this clarifies my post.

Thanks, Marco. I follow you and had not considered that as a possibility. How might power consumption be affected if both the CPU and voltage were lowered, and would not that make the device unstable?

MarkAtHome wrote:Thanks, Marco. I follow you and had not considered that as a possibility. How might power consumption be affected if both the CPU and voltage were lowered, and would not that make the device unstable?

Mark,

I didn't understand well your question. Can you please explain better? (english is not my mother language...)
thank you

marco.palumbi wrote:Said that, the aim of my post wasn't to focus on which frequencies/voltages functions or are the best for this device.
I would focus on the fact that lowering the CPU speed without lowering the voltage, the power consuption decreases.

MarkAtHome wrote:Thanks, Marco. I follow you and had not considered that as a possibility. How might power consumption be affected if both the CPU and voltage were lowered, and would not that make the device unstable?

marco.palumbi wrote:I didn't understand well your question. Can you please explain better? (english is not my mother language...)thank you

Marco -- You are doing quite well, compared to how I might butcher a language other than English!

You said that "lowering the CPU speed without lowering the voltage, the power consuption decreases". So, presuming this is so, I was asking whether lowering the CPU frequency AND lowering the voltage (you said without lowering it), would, therefore, make the device unstable.

MarkAtHome wrote:I was asking whether lowering the CPU frequency AND lowering the voltage (you said without lowering it), would, therefore, make the device unstable.

It depends Mark. Manufacturer sets the default frequency and voltage table as safe minimum. Every CPU and handset have to work with it. Your CPU may be capable of working Wirth slightly lower voltage, much lower voltage or may become unstable after any change. Underclocking shoud not affect this in any manner.
So if it became unstable or not it depends ir particullar CPU you jad on your board.

MarkAtHome wrote:I was asking whether lowering the CPU frequency AND lowering the voltage (you said without lowering it), would, therefore, make the device unstable.

donblazello wrote:It depends Mark. Manufacturer sets the default frequency and voltage table as safe minimum. Every CPU and handset have to work with it. Your CPU may be capable of working Wirth slightly lower voltage, much lower voltage or may become unstable after any change. Underclocking shoud not affect this in any manner.
So if it became unstable or not it depends ir particullar CPU you jad on your board.

also the min operating frequency is a design limit (and thus as donblazello said about voltage, any single chip may react in different way)
min frequency may impact the refresh time of of dinamic storages for example...
about lowering both frequency and voltage must be said that, "generally speaking", to achieve higher speed you must increase the voltage (we can say that at higher voltages you increase the current that discharge parassitic capacitances inside the chip and thus you can switch faster) and lowering the clock you can lower the voltage.
about power consumption, as I stated in other post, lower the voltage is more effective than lower the frequency because power goes with the square of voltage while it decrease linearly with frequency .
Must also be said that for power saving purpose often the frequency is lowered to permit voltage lowering, so lowering only the frequency is not much effective (also becouse you need much time to make the same task....)

this is the theory.....

coming back to the Mark's question: every chip is different. Chip manufacturers gives the maximum and minimum that are warrant to function in every chip given the difference that may be between each.

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MarkAtHome wrote:You said that "lowering the CPU speed without lowering the voltage, the power consuption decreases". So, presuming this is so, I was asking whether lowering the CPU frequency AND lowering the voltage (you said without lowering it), would, therefore, make the device unstable.

donblazello wrote:It depends Mark. Manufacturer sets the default frequency and voltage table as safe minimum. Every CPU and handset have to work with it. Your CPU may be capable of working Wirth slightly lower voltage, much lower voltage or may become unstable after any change. Underclocking shoud not affect this in any manner. So if it became unstable or not it depends ir particullar CPU you jad on your board.

marco.palumbi wrote:coming back to the Mark's question: every chip is different. Chip manufacturers gives the maximum and minimum that are warrant to function in every chip given the difference that may be between each.

While I am convinced you are all correct and make valid points this subject remains, in my view, a complex issue. Certainly too complex for the average user like myself. As a result, I tend to rely on more knowledgeable people than myself - one of those being Francisco Franco (yes, the fellow who puts out some excellent kernels). Speaking of things he will not do or add to his kernel Francisco listed (emphasis added by me):

Don't bother asking for this as I will ignore you:
- GPU overclock
- Lower UV limit (default is 700mV)
- Lower CPU frequencies (minimum is 384MHz)
- sleep2wake
- Stupid governors
- MIUI support

While the lower voltage and CPU frequency limits shown above are specific to a device (Nexus 4 in this case) I suggest that it does illustrate the fact that some low numbers are, in his view, not worth considering or implementing.

Food for thought.

NYLimited wrote:


While I am convinced you are all correct and make valid points this subject remains, in my view, a complex issue. Certainly too complex for the average user like myself. As a result, I tend to rely on more knowledgeable people than myself - one of those being Francisco Franco (yes, the fellow who puts out some excellent kernels). Speaking of things he will not do or add to his kernel Francisco listed (emphasis added by me):



While the lower voltage and CPU frequency limits shown above are specific to a device (Nexus 4 in this case) I suggest that it does illustrate the fact that some low numbers are, in his view, not worth considering or implementing.

Food for thought.

I agree with you NYLimited that this is an unuseful argument. My aim was only to add some theory...
particularly I would point the fact that, always in theory, also lowering the clock without touching the voltage the consumption lowers despite as someone thought.

undervoltage and underclock affects only the low power state of the CPU. The state in wich the CPU sinks about 5mA.
Also if we can gain may be 2mA in this state, during a working day we gain about 2mA*16hour = 32 mA/hour that it is few respect about 1200 mA/hour of the battery ...