Re: So, what's the status on the recent patches here?

Preece Scott-PREECE
2006-08-31T00:22:56Z

> From: Pavel Machek [mailto:pavel@ucw.cz]
> > It's an interesting question, and one we (Motorola) don't have hard
> > data to support, yet. Our current implementation remembers
> the OP in
> > use before sleeping and resumes at the same OP. The
> argument is that
> > this corresponds to an application that is doing work at a
> > steady-state level (say decoding video), but that has a
> brief pause to
> > wait for I/O or a timer (say, pausing until the next frame
> time); then
> > it makes sense that the level of effort required on resume
> will be the
> > same as before sleeping.
>
> We may have confusion here.
>
> On PC, it is definitely not possible to enter sleep state
> between frames of video... because video is powered off.
>
> On PC, sleep states are *system* sleep states. CPU sleep
> states exist, too, but that's in-kernel implementation
> detail. They are called C1..C4.
---

Well, we have some hardware where we can sleep everything but
memory and some where we can also leave the display active (and
backlit). In fact, however, today the latency for going to sleep
is too great to do so between frames, so we just do a wait there.
We would LIKE to be able to sleep there at some point in the
future and would prefer a power model that made that cleanly
part of a continuum of operating points.

However, we definitely DO sleep (with self-refreshing RAM) during
relatively short periods, with the wakeup resulting from an
interrupt from the RTC (which is self-powered and is set
to timeout at the next scheduled timer when we go to sleep)
or another hardware interrupt. We think of this as a system-level
sleep state.

I'm not sure how you distinguish between a "system" sleep state
and a "CPU" sleep state - seems like there's a collection of
things that can be shut down or not; except for true OFF, there's
always something on.

Scott