On Sun, 6 Jun 2010, Brian Swetland wrote:
The savings in airplane mode (apart from preventing data connections,
which saves power by preventing data-hungry background apps from doing
much) is the difference between standby with radio (3-5mA) and without
(1-2mA). I'm not suggesting that airplane mode is a typical case,
just using it as in illustration of the more extreme standby case.
for the sake of discussion, let's say that standby is 5ma and full
operation is 500ma and a minimal wakeup is 0.1 sec. these are probably
fairly pessimistic numbers.
waking up every second would be awake 10% of the time, so in an hour you
would use .9*5mA + .1*500mA = 4.5mA +45mA = 49.5mAH
waking up every 10 seconds would be awake 1% of the time, so in an hour
you would use .99*5mA + 0.01*500mA = 4.95mA + 5mA = 9.95mAH
waking up every 100 seconds would be awake 0.1% of the time, so in an hour
you would use .999*5mA + 0.001*500mA =4.995mA + 0.5mA = 5.495mAH
waking up every 1000 seconds would be awake 0.01% of the time so in an
hour you would use .9999*5mA + 0.0001*500mA = 4.9995mA + 0.05mAH =
5.0495mAH
now if you have a 1000mAH battery (small, but reasonable for a smartphone)
your standby life would be
.1 second wakeup (on continuously) = 2 hours
1 second wakup = 20 hours
10 second wakeup = 100 hours
100 second wakeup = 182 hours
1000 second wakeup = 198 hours
if you could shrink the time awake to 0.01 second per wakeup you would
shift this all up a category (and avoiding the need to wake everything up
to service a timer would help do this)
this effort very definantly has diminishing returns as you go to larger
sleep periods as the constant standby power draw becomes more and more
dominating. someone mentioned that they were getting the sleep time of
normal systems up past the 1 second mark with the 10 second mark looking
very attainable. that is where you get the most benifit for whatever
changes are needed. getting up to a 2 min sleep time really gives you
about all the benifit that you can get, going from there to 15 min makes
very little difference.
don't let chasing the best possible sleep time prevent you from
considering options that would be good enough in time, but would
drastically reduce the maintinance effort (as things could be upstreamed
more easily), and would be usable on far more systems.
David Lang
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