Re: [RFC PATCH 0/4] Add support for detection

[Amadeusz Sławiński <amadeuszx.slawinski@xxxxxxxxxxxxxxx>]

On 10/18/2024 7:15 PM, Jaroslav Kysela wrote:
> On 18. 10. 24 16:16, Amadeusz Sławiński wrote:
>
> > Our use case is to:
>
> Inlined my proposal:
>
> > 1. Program DSP with all pipelines it needs to implement whole scenario
> > (hw_params)
>
> SNDRV_PCM_IOCTL_HW_PARAMS
>
> > 2. Perform additional configuration from usespace
>
> Can be done using control API (/dev/snd/controlC*). E.g. We have already:
>
> numid=19,iface=PCM,name='ELD',device=3
> numid=32,iface=PCM,name='Playback Channel Map',device=3
>
> Those controls can be R/W as you like.
>
> > 3. Start detection pipelines
>
> SNDRV_PCM_IOCTL_PREPARE

Will check, but from what I recall streams should not be started in 
prepare due to it being used for xrun recovery, but maybe it doesn't 
matter for detection ones.

> > 4. Wait for event to happen (it can take however long necessary, for
> > example hours)
>
> Can be done using control API (/dev/snd/controlC*). There is a mechanism 
> for event handling already.
>
> Something like (boolean type):
>
> iface=PCM,device=2,name="Event X"   # first event type
> iface=PCM,device=2,name="Event Y"   # second event type ...
>
> The PCM stream may be active only when at least one event from the above 
> set is active.
>
> > 5. When event happens start drain pipelines and process data in
> > userspace likes in standard capture scenario
>
> SNDRV_PCM_IOCTL_START
>
> The driver may set the correct timestamp when the capturing was started. 
> The sample buffers are already allocated and ready for transfers, so we 
> can assume that the time window between the event notification (event) 
> and START ioctl is small, so no samples should be lost.
>
> > 6. When no more data is needed, either stop drain pipelines and go back
> > to 3 or just close stream
>
> SNDRV_PCM_IOCTL_STOP / DRAIN, SNDRV_PCM_IOCTL_HW_PARAMS or close(fd)
>
> Basically, I think that this extension can be implemented with minimal 
> changes to the PCM API - it's just about to slightly extend existing APIs.
>
>                  Jaroslav