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Subject: Re: Power Efficiency Tradeoffs

Re: Power Efficiency Tradeoffs

From: Burelli Luca <>
Date: Mon, 21 Jan 2008 23:10:39 +0100 (MET)

On Sat, 12 Jan 2008, Catalin Patulea wrote:

> - I believe (correct me if I'm wrong) that, in general, power
> consumption is proportional to the core frequency. Let the power
> consumptions of the cores be P_1 = k*f_1 and P_2 = k*f_2.

An accurate estimation of power consumption in digital electronics is not
so easy to figure out. However, as a rule of thumb, you may assume there's
a constant power dissipation which is due to leakage (non-ideal switches
allowing current to flow even where and when it should not), and a
"dynamic" power dissipation that is proportional to Vdd (the switching
voltage) and to _the square_ of the switching frequency. So the above
would be better written as P_1 = P_{1,leak} + k * f_1^2, meaning that if
you run the CPU twice as fast, you need four times the energy (ignoring
leakage). That's why clock throttling helps _a lot_ in reducing battery

Hope I remembered things correctly from my University classes :-)

Best to everybody and thanks for your work on Rockbox!

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Received on 2008-01-21

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