power management experiences with joyride-1572

[Jordan Crouse]

On 26/01/08 21:47 +0000, david at lang.hm wrote:
> On Fri, 25 Jan 2008, Richard A. Smith wrote:
> 
> > Chris Ball wrote:
> >
> >>   >> Can I wake up 10 seconds from now?  Is there a timer in any of the
> >>   >> hardware that is left running?
> >>
> >>   > Yes, but the software does not support this yet.  See bug #4606:
> >>   > http://dev.laptop.org/ticket/4606
> >>
> >> We don't *use* the southbridge RTC wakeup, but it's not strictly true
> >> that we don't support it.  You can set your own wakeups easily:
> >>
> >>    # rtcwake -s 120
> >>    <after 30s, the laptop should suspend due to idleness>
> >>    <after another 90s, the laptop should wake itself>
> >>
> >> rtcwake is in the OLPC build already.
> >>
> >> - Chris.
> >
> > RTC wakeups have a chance of hitting #1835 because the EC cannot prevent
> > the short cycle of the control line to the voltage regulator so we don't
> > use them.  Andres has discussed prohibiting RTC wakeups in kernel space
> > but I suggested we put that in the "don't do that" category since he has
> > higher priority stuff to worry about.
> >
> > The safe way to schedule a future wake up will be to use a EC timer.
> >
> > The framework for this exists but I don't have the kernel facing EC
> > command plumbed yet.  This timer will allow you to schedule a wakeup
> > with about 10ms resolution up to 24 days in the future.
> 
> what is the shortest time that a sleep (followed by a wakeup from the EC 
> timer) can be programmed?
> 
> would it make sense to hack the kernel so that if all timers are set to 
> fire more than this far in the future it wakes a user task that can decide 
> to sleep

See also 'cpuidle' [1].

Jordan

[1] - http://lwn.net/Articles/221791/