[Community-news] OLPC News (2008-02-09)

[Chris Ball]

Hi,

   > The good news is that the 2W total matches what olpc-logbat reports
   > as being the average for a 4.5 hour uninterrupted suspend session
   > so measured matches reality.  The bad news is that this works out
   > to only about 8.5 hours of battery life with no wakups.

My own perspective here is that 8.5 hours in the idle case isn't bad
news for where we're at -- Update.1 should still end up doubling the
battery life seen by mostly-idle XOs.

   > To get to greater than 10 hours, we are going to have work out
   > methods of determining when we have been inactive for extended
   > periods and turn off both the LCD and backlight under those
   > conditions.

Once the EC timers are exposed, we're only a few lines of timer code¹
and a few lines of OHM code² away from having this.  I hope it'll be
one of the first changes we land once Update.2 opens, and it should
have a big effect on battery life.

(Even if the EC timer code takes a while to appear, I recall hearing
that the Southbridge RTC timers are unsafe only in the presence of a
very short delta between suspend and wakeup, which this particular
scheme would never generate.)

- Chris.

¹:  Set a timer for +ten minutes before suspending, cancel it if we're
    woken up before ten minutes has passed.  (To avoid having to do time
    calculations to find out whether a timer woke us up, the EC could
    just tell us whether our wakeup source was a timer.)
    
²:  If woken up by the timer, turn off the screen and suspend; at other
    times, if the screen is off when we wake up, turn it on.
-- 
Chris Ball   <cjb at laptop.org>