Question about Undervolting, Low Clocks and Idle Power

[Guest xaueious]

I know phh has mentioned that the CPU really doesn't consume much power at idle no matter what voltage you tweak this at, but where can I find more reading on this?

Is it worthwhile to be clocked at 128MHz at 0.85v or not? I've been running this for the last two weeks already, but I haven't really sat down and analyzed my battery life.

Can someone give input on this?

[Guest Quipeace]

I know phh has mentioned that the CPU really doesn't consume much power at idle no matter what voltage you tweak this at, but where can I find more reading on this?

Is it worthwhile to be clocked at 128MHz at 0.85v or not? I've been running this for the last two weeks already, but I haven't really sat down and analyzed my battery life.

Can someone give input on this?

Well, there's much more to it, but simply put the processor goes into a powersaving mode. There's lots about cpu states on wikipedia, most are geared towards desktop processors, but the main idea is the same, so if you want to know more that's a good place to look.

[Guest xaueious]

I have read a little about that. So undervolting the CPU for idle power consumption has limited use because the CPU already has internal mechanisms to reduce idle power consumption?

http://www.hardwaresecrets.com/article/611

But if the CPU was not idle, then it would be running at at least the lower power state defined in the frequency table then?

Edited August 5, 2010 by xaueious

[Guest xaueious]

Um... Bump?

[Guest eumate]

Voltage reduction has obviusly the strongest impact when the cpu is full load.

For standby or sleep power reduction, you can achieve better result 'turning off' parts of cpu that aren't required when there're little or no instructions to process, and this is what is done by the scorpion. It even disables the main PLL.

Turning it off, only small pieces of cpu are under power, so undervolting has really less impact.

[Guest xaueious]

Thanks for the info.

I guess the burst processing stuff I read earlier also affects this.

http://alienbabeltech.com/main/?p=17125

So I'll just leave the settings alone.

I am finding however than 128 MHz is sufficient as the lowest frequency if it's just playing music. But beyond that, I don't see the phone entering the 128 MHz state for a long time because by then it will probably hit idle state.

Right idea?

Edited August 6, 2010 by xaueious

[Guest phhusson]

So I'll just leave the settings alone.

I am finding however than 128 MHz is sufficient as the lowest frequency if it's just playing music. But beyond that, I don't see the phone entering the 128 MHz state for a long time because by then it will probably hit idle state.

Right idea?

Qualcomm says NOT to use 128MHz:

https://www.codeaurora.org/gitweb/quic/la/?...8ac5ea;hb=froyo

around line 126.

It speaks about WFI, but it also applies for normal operating mode.

[Guest xaueious]

Good one. I wont mess with those then.

So I effectively nuked my power collapse mode...

But what that also means is that whatever voltages I am setting to 128MHz is actually being applied, but effects are minimal since it's just a PC mode... That's like a couple of clicks...

Meh

I hope there's no harm in me not using 576MHz and using 460MHz instead for that intermediate frequency, and eliminating 768MHz altogether with clock to 921 MHz.

That just shifts my clocks, and I leave that lower range alone...

PS:

See? I don't know what we'll do without you :)

I'm still an idiot

Edited August 6, 2010 by xaueious

[Guest phhusson]

Good one. I wont mess with those then.

So I effectively nuked my power collapse mode...

But what that also means is that whatever voltages I am setting to 128MHz is actually being applied, but effects are minimal since it's just a PC mode... That's like a couple of clicks...

It could be useful for really low consumption mode, or idle mode (ie not standby, but cpu doesn't do anything yet ...) like music playing.

But I don't think it can do proper music playing at 128MHz anyway.

Meh

I hope there's no harm in me not using 576MHz and using 460MHz instead for that intermediate frequency, and eliminating 768MHz altogether with clock to 921 MHz.

If I understand the code properly, this change seems fine, but I wouldn't bet on it :)

[Guest xaueious]

Actually it plays music just fine at 128MHz. Not sure if it offloads the workload. I set SetCPU to 128MHz locked, and polled with cat /proc/cpuinfo.