[Power] Waking XO-1.75 with RTC

[James Cameron]

George Hunt wrote (on power at lists.laptop.org):
> Does anyone have experience waking up an XO via the RTC?  Manual
> entries for rtcwake make it sound pretty easy. But there's no real
> substitute for experience.

rtcwake with a delta time works for me on XO-1.75, you can see a
rather technical example in /runin/runin-sus, but it boils down to

	sudo rtcwake --seconds 60 --mode mem

I'm not sure if it works with an absolute time ... I doubt it, but
I've not had a moment to try it.  We don't have a need for absolute
time wakeup in the OLPC OS builds.

You can easily use a delta time sleep until the clock is close to
start of school day.

The system will wake if there is another reason to; like keyboard,
touchpad, network, or battery state of charge change.  This is another
good reason to use a delta time.

The following is deeper detail than is needed:

Sridhar Dhanapalan wrote (on power at lists.laptop.org):
> Interesting idea. My understanding is that the XO-1.75 has two RTCs -
> not sure why.

One is inside the CPU, but it is unpowered if the system is off.  It
is used by rtcwake, and remains powered during suspend.  Access to it
is fast.

The other is external to the CPU and is powered even when the system
is off, using a battery, so that it keeps time.  It cannot be used to
wake the system.  Access to it is over a serial bus.  This is the RTC
maintained by Open Firmware.

CC: devel at lists.laptop.org 'cause this is a more general question than
power.

-- 
James Cameron
http://quozl.linux.org.au/