Powerd comments

Paul Fox pgf at laptop.org
Tue Mar 16 16:33:06 EDT 2010

hello james --

james wrote:
 > >     - if on battery, the laptop will auto-shutdown after its been
 > > 	asleep for 1 hour.  if plugged in, it will sleep forever.
 > I've used powerd and really love how it works, especially how easy it
 > is to configure and hack. I agree with the design decisions for the
 > most part but auto-shutdown after sleeping for an hour, seems like a
 > problem. When someone puts their laptop to sleep they expect that
 > they'll be able to resume. The XO uses so little power in sleep mode
 > and booting takes long enough on the XO that maintaining the ability
 > to quickly resume should take priority. I understand that there is a

this timer is certainly a prime candidate for being made longer, if
people think it should be.

 > desire to avoid hard shutdowns due to empty battery, but isn't there
 > way to make it sleep until battery is criticaly low. I know that it is
 > difficult to poll battery level when in sleep mode but maybe you could
 > have rtcwake bring the computer out of sleep not after 1 hour but
 > after a time powerd estimates that the battery can support sleep.

in fact, powerd already does a partial job of this.

the wakeup events currently available are the "SOC"
(state-of-charge) event, which is emitted every time the battery
capacity changes by 1%, and the "critical" event, which is
emitted when the battery is critically low.

if the battery has less than 20% capacity left when the system is
put to sleep, powerd will enable the SOC event to wakeup and check the
battery condition periodically in order to shutdown properly.  on
XO-1.5 we may also be able to use the "critical" event -- on XO-1 that
event only comes when the battery is too weak to actually run the
system -- responding to it causes an immediate crash.

 > Since we have power consumption controlled in sleep it should be easy
 > to estimate how long we can keep the computer in suspend at the
 > battery level immediately before sleep. Wake a little short of this
 > time and poll the battery and see if we need to shutdown, if not
 > snooze until shortly before we think the battery will run out. Its all
 > there in powerd already except shutdown time should be determined by a
 > function to estimate how long the battery will last in sleep instead
 > of reading from the config file.

yes, i'm sure we can do better than we're doing now.

 > Also, is there a reason the config file has to be in /etc/ and not
 > /home/olpc . It seems like it would be useful to let the user edit
 > powerd settings as user and not as root.

well, it's a system service.  but perhaps something can be done.


 > Thanks again for all the work on powerd
 > james
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 paul fox, pgf at laptop.org

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