Re: Attempted summary of suspend-blockers LKML thread

From: Brian Swetland
Date: Thu Aug 05 2010 - 21:23:15 EST

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).

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