Power envelope (was Re: radio off guarantee?)

[Jim Gettys]

On Tue, 2007-09-18 at 12:12 -0400, Mike C. Fletcher wrote:
> John Watlington wrote:
> >>> Suppose I'm someplace where I don't expect or want to do any mesh
> >>> networking.
> >>> How much would turning off the radio help battery life?
> >>>       
> >> Last I checked, the effect was very small.  There will be occasional
> >> scans as the unit hunts around for nearby radios.  One could save more
> >> by making those scans back off rather than provide a UI element.
> >>     
> >
> > We see 700 to 800 mW consumed by the mesh interface, and as with most
> > WiFi interfaces, receiving consumes as much power as transmitting.
> >   
> Isn't that about 1/2 of our total power budget?  .7 to .8 W on a < 2W 
> machine?  I'd thought the Marvell chip was supposed to be down in the 
> .3W range.  Obviously haven't been following the hardware closely 
> enough.  (http://wiki.laptop.org/go/Power_Management is where I got the 
> .3W idea).  Is that .7W something we'll be able to bring down with 
> software to reduce collisions or the like?  University of Toronto's 
> system's group has algorithms that optimise for power savings by 
> reducing collisions, if that would help.

The current firmware has not yet been optimized, and is consuming much
more power than it should once that is done.  And future wireless will
also help.
                           - Jim

-- 
Jim Gettys
One Laptop Per Child