[Gllug] iPhone 4 or Android phone

James Courtier-Dutton james.dutton at gmail.com
Fri Jul 16 21:41:35 UTC 2010

On 16 July 2010 22:05, Nix <nix at esperi.org.uk> wrote:
> On 16 Jul 2010, general told this:
>> On 16/07/10 11:16, James Courtier-Dutton wrote:
>>> There is a way round the noise caused by smartphone CPUs, and that is
>>> by moving them to a new CPU technology called async clocking instead
>>> of sync clocking.
>>> Async clocked CPU are somewhat expensive at the moment, but hopefully
>>> soon this will improve.
>> Interesting then that my 8 year old P4 motherboard supports it ;) When I
> I think that's spread-spectrum clocking, making the clock signal very
> slightly irregular (roughly). It is an RF noise reduction technique, but
> quite different from async clocking, in which there is no single clock
> signal per se at all.
> IIRC people aren't pouring money into async clocking because of radio
> noise, but because it would let CPUs run much closer to full utilization
> all the time. However it's bastard hard.

Some of their biggest customers are ones where the RF noise is a major concern.
For example, smart cards that have a crypto function. Lower RF noise
makes for harder side channel attacks.
The cost benefit trade offs for 'full utilization" or not, do not
favour async yet.
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