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

["Amadeusz Sławiński" <amadeuszx.slawinski@linux.intel.com>]

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
>