Paul Fox pgf at
Thu Aug 6 22:58:57 EDT 2009

wad wrote:
 > The context is that we are trying to ensure that an Maximum
 > Power Point Tracking algorithm can be implemented on the DC
 > power input of the XO-1.5.
 > On Aug 5, 2009, at 10:56 PM, Richard A. Smith wrote:
 > > John Watlington wrote:
 > >
 > >> The problem comes from the need for the algorithm to start
 > >> from a position of low current drain.  The MPPT algorithm
 > >> should probably be disabled when the laptop is running and
 > >> the battery is below some threshold (say 10 -15% ?)
 > >
 > > Yep.  I don't think it will matter though.  The core of the
 > > problem is that our peak CPU power draw is > 10W where on
 > > gen 1 is was <=10W and we aren't going to fix that.
 > We should play with having the power daemon clock down the CPU in  
 > some cases.

how much would that save?  how fast would the reaction time need
to be?  (i.e., how responsive does the MPPT algorithm need to be?

 > Perhaps modifying adding a "solar power provided or removed" subtype  
 > to the Battery Status Change SCI interrupt from the EC ?

how would this be detected automatically?  by voltage level?

 > This could be used to limit the peak processor clock when the battery  
 > is very low.
 > Limiting the peak processor clock when the battery is very low
 > and we don't have any DC input might extend the battery life
 > slightly as well.

how much remaining runtime are we talking about, when we talk about
"very low"?  and again, how much can we affect the end result?

 paul fox, pgf at

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