Re: Attempted summary of suspend-blockers LKML thread

[david]

On Thu, 5 Aug 2010, Brian Swetland wrote:

> On Thu, Aug 5, 2010 at 6:01 PM,  <david@xxxxxxx> wrote:
> > On Thu, 5 Aug 2010, Brian Swetland wrote:
> > > On Thu, Aug 5, 2010 at 5:16 PM, Â<david@xxxxxxx> wrote:
> > > > > > So for an mp3 playback, does an Android suspend between data fetches?
> > > > >
> > > > > It can if the latency is long enough (which is why I point out low
> > > > > power audio which is usually high latency). ÂFor low latency (system
> > > > > sounds, etc) 10-25ms between buffers it's not practical to fully
> > > > > suspend but we will go to the lowest power state in idle if possible.
> > > >
> > > > the playback is able to continue even with all the clocks stopped? that
> > > > surprises me. I would hav expected it to be able to sleep while playing
> > > > audio, but not do a full suspend.
> > >
> > > Obviously not all clocks are stopped (the DSP and codec are powered
> > > and clocked, for example), but yeah we can clock gate and power gate
> > > the cpu and most other peripherals while audio is playing on a number
> > > of ARM SoC designs available today (and the past few years).
> >
> > does this then mean that you have multiple variations of suspend?
> >
> > for example, one where the audio stuff is left powered, and one where it
> > isn't?
>
> While the cpu (and the bulk of the system) is suspended, it's not
> uncommon for some peripherals to continue to operate -- for example a
> cellular radio, gps, low power audio playback, etc.  Details will vary
> depending on the SoC and board design.  It's not so much a different
> suspend mode (the system is still suspended), just a matter of whether
> a peripheral can operate independently (and if it is lower power for
> it to do so).

this helps, but isn't quite what I was trying to ask.

on a given piece of hardware, does suspend always leave the same 
peripherals on, or do you sometimes power more things down than other 
times when suspending?

David Lang