radu
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Re: CPU voltage control

Fri Nov 25, 2011 7:07 am

Will it be possible to set the CPU voltage by software? If yes, within what limits? What is the default?

radu
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Re: CPU voltage control

Sat Nov 26, 2011 6:29 pm

Sorry for the bump, but I would really like to know this, it can make a huge difference in many projects.

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liz
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Re: CPU voltage control

Sat Nov 26, 2011 7:01 pm

Default is 1.2v, and I'm afraid you can't change it in software. Changing the CPU voltage downwards would stop the chip from working, and upwards would reduce the chip lifetime unacceptably.
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jamesh
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Re: CPU voltage control

Sat Nov 26, 2011 7:37 pm

What are you trying to do?

The GPU power management already is pretty much as good as it gets - are you just talking about the Arm side?
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radu
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Re: CPU voltage control

Sat Nov 26, 2011 7:53 pm

Well, I see two scenarios.
1. Say you want something that requires very little stand by power, but has some peaks where it requires more power. So you can underclock and undervolt the cpu when it is idle.
2. If you want to overclock it to higher than normal speeds you will have to increase the voltage a bit (say, to reach 1Ghz+ speeds).
And yes, I am talking mostly about the ARM side.

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liz
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Re: CPU voltage control

Sat Nov 26, 2011 7:58 pm

You won't be able to make the ARM work at 1Ghz+ without compromising its life expectancy. It's not rated for that sort of voltage.
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radu
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Re: CPU voltage control

Sat Nov 26, 2011 8:01 pm

That's ok, it's not like it will live forever. Besides, it doesn't have to run at higher clocks 24/7. With some basic heatsink it should last more than its useful life.

na1pir
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Re: CPU voltage control

Sun Nov 27, 2011 1:41 pm

I don't think heat sink would do you any good because of PoP memory.

jamesh
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Re: CPU voltage control

Sun Nov 27, 2011 1:58 pm

Yes, as its a PoP on package it doesn't react in the same way of a pure CPU. A heatsink would help I guess, but won't be as effective as you might think.
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Burngate
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Re: CPU voltage control

Sun Nov 27, 2011 4:53 pm

There's a whole thread on overclocking which also mentions overvolting
http://www.raspberrypi.org/for.....&t=55
though I couldn't find a mention of how that was achieved.
Quote on that thread from Gert on Aug 9:
As real engineers, yes, we have overclocked the ARM. But we can't tell you about it as this is an open website and one of our marketing managers might read it. They will immediately sell it with that spec. ;) Yes, we have overclocked the SDRAM but we raised the operating voltage beyond the safety limit. So if you want an ultra fast top-of-the-range Raspberry you can have, for a short while until it is "baked".

radu
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Re: CPU voltage control

Sun Nov 27, 2011 6:59 pm

Well, I have a N900, and I overclocked my CPU from 650 to 850 MHZ, and so far no problems. Some people overclocked their N900 to 1Ghz or so, and except for it getting pretty warm, there were no reports of any phone breaking. I don't think that having the RAM on top will be a big issue, because we are talking about low power anyway. But a heatsink will help a bit, it will reduce the temperature by a few degrees.

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