[mythtv-users] CPU power (was Possible small HD frontend)

stuart stuart at xnet.com
Sat Mar 22 15:22:01 UTC 2008



Phil Bridges wrote:
> On Sat, Mar 22, 2008 at 10:31 AM, Brian Wood <beww at beww.org> wrote:
>>
>>  On Mar 22, 2008, at 8:25 AM, Brian Phillips wrote:
>>  >
>>  > Seems logical as the power consumption for an idle transistor is very
>>  > minimal, if completely unnoticeable.  Transistors use the bulk of
>>  > power when
>>  > they need to make a state change.  The clock speed only affects the
>>  > clock
>>  > signal, which is a minute number of transistors when you compare it
>>  > to the
>>  > cache on chip, ISA transistors, etc.  If you clock the chip slower,
>>  > you
>>  > aren't saving any noticeable amount of power because you are only
>>  > reducing
>>  > the number of state changes in the clock generation and processing
>>  > transistors.
>>  >
>>  > If you are actually processing something, you are changing the state
>>  > of the
>>  > majority of transistors on the chip and therefore you will see the
>>  > most
>>  > power usage.  By slowing the clock, you aren't saving anything.  The
>>  > total
>>  > amount of power needs to be spent to process your instructions, you
>>  > are just
>>  > lengthening the time over which those instructions are processed.
>>  > You might
>>  > see lower instantaneous power usage, but summed over time you will
>>  > see very
>>  > little difference in power usage.
>>  >
>>  > This is all assuming minimal power lost to generation of heat, which
>>  > AMD is
>>  > losing the battle on due to trying to keep up with Intel's
>>  > technology.  Or
>>  > so I hear.
>>
>>  So slowing the clock is just a thermal issue? The same amount of work
>>  over a longer time would require heat to be removed at a slower rate,
>>  thus allowing slower fans?
>>
>>  Slowing the clock is certainly touted as "green" in a lot of circles,
>>  but it wouldn't surprise me if it is marketing and not engineering. I
>>  seriously doubt the power saved by slowing the fan(s) would be
>>  significant.
>>
>>  beww
>>
> 
> Doesn't it also use fewer W from the power supply?

Picking a clock speed is like playing a game.  Pick high and you need 
more cooling, pick low and your front end will stutter.

That said, if you're that set in finding a silent front end, sacrifice 
features and use the MythTV UPNP server with a SigmaDesign/Syabas box. 
There are literally dozens to choose from:
(list from WizD web site)
> Networked Players :
> - I-O Data LinkPlayer
> - Buffalo LinkTheater
> - Snazio Net Cinema
> - H&B DNX-8620
> - Quartek WHD-500
> - Quartek I-Box 800
> - Transgear DVX 700
> - Transgear DVX 500
> - Pinnacle SC 200
> - Omisys DVD PN210V
> - DigitalRise Xstream

If you want more features, perhaps you could look into incorporating 
WizD or SwissCenter features into MythTV.  The above players will 
probably be able to handle the enhancements.  However, I would guess the 
reaction time will be a concern as well as no foreseeable way to 
implement features such as commercial skipping.






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