[alsa-devel] proposal: snd_pcm_start_at()

[Tim Cussins]

Hi Takashi,

On 06/10/14 10:45, Takashi Iwai wrote:
> At Fri, 03 Oct 2014 17:24:22 -0500,
> Pierre-Louis Bossart wrote:
>>
>> On 10/3/14, 7:00 AM, Tim Cussins wrote:
>>> Hi Peirre,
>>>

>>> The pcm hardware for the new platform can start rendering when a compare
>>> register matches a hw counter (driven by the audio clock). This allows
>>> for starting with frame-accurate timing.
>>
>> Interesting. I wonder if you actually need a new extension for this, you
>> could write the timestamp in an ALSA control and implement your .trigger
>> function by using the contents of the control, i.e. delay the actual
>> start. it wouldn't be generic but your hardware isn't either.
>
> Well, your suggestion sounds really tricky.  The trigger is supposed
> to trigger the stream immediately, and the delay isn't considered
> there in principle.  The system can work with delays, but it's not in
> a form of the initial design.
>
> I think some synchronized triggering mechanism is missing in API, too.
> There has been a similar request from others in the past (Digigram
> wanted to have such a feature), so maybe it's not so uncommon
> scenario.
>
> This would be a good topic to be discussed in the upcoming audio
> mini-summit, but both of you won't be there, right?
>

I didn't have any plans to be at the mini-summit, but Glasgow isn't too 
far away...

>
> Takashi
>