[Gllug] iPhone 4 or Android phone

[Richard Jones]

On Fri, Jul 16, 2010 at 10:41:35PM +0100, James Courtier-Dutton wrote:
> 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.

I'm quite convinced that "James Courtier-Dutton" is an Eliza-like AI
experiment which scrapes content from random Google searches.  Needs a
bit of tuning IMHO.

I have actually built both synchronous and asychronous hardware for a
research laboratory (VMEbus was fun!).  As Nix quite rightly says,
asynch circuits are not commonly used, not because of some airy-fairy
"cost benefit trade offs", but because it is "bastard hard" to make
them work at all.

Rich.

-- 
Richard Jones
Red Hat
-- 
Gllug mailing list  -  Gllug at gllug.org.uk
http://lists.gllug.org.uk/mailman/listinfo/gllug