PCM extra attributes

PCM extra attributes

[Vinod Koul]

Hey Takashi,

We were looking to find the substream index in the userspace for the device
opened (in case we support multiple substreams and mix them). Since we also
wanted to have some specific alsa controls for each substream the problem of not
knowing substream in usermode make stuff interesting!

I was pointed to an old RFC of yours [1] and it fits my needs. I can get the
substream index using this and program the alsa controls.

Now reading the archive looks like it was note merged. Would be okay to do so
for above case. I can resurrect the patchset if you would like...

Thanks
~Vinod

[1]: http://mailman.alsa-project.org/pipermail/alsa-devel/2009-June/018651.html

-- 

Re: PCM extra attributes

[Raymond Yau]

>
> We were looking to find the substream index in the userspace for the device
> opened (in case we support multiple substreams and mix them).


http://www.alsa-project.org/alsa-doc/alsa-lib/group___p_c_m___info.html

snd_pcm_info_get_subdevice() - Get subdevice from a PCM info container

snd_pcm_info_get_subdevice_name() - Get subdevice name from a PCM info
container

snd_pcm_info_get_subdevice_count() - Get subdevices count from a PCM info
container

snd_pcm_info_get_subdevice_avail() - Get avail subdevices count from a PCM
info container

snd_pcm_info_set_subdevice - Set wanted subdevice inside a PCM info
container


>
> Since we also wanted to have some specific alsa controls for each
> substream the problem of not knowing substream in usermode make stuff
> interesting!
>

The subdevices of a device need to same format , rate , channels, period
and buffer constraints


http://git.alsa-project.org/?p=alsa-tools.git;a=tree;f=hwmixvolume

Re: PCM extra attributes

[Jaroslav Kysela]

Date 24.7.2013 19:09, Vinod Koul wrote:
> Hey Takashi,
> 
> We were looking to find the substream index in the userspace for the device
> opened (in case we support multiple substreams and mix them). Since we also
> wanted to have some specific alsa controls for each substream the problem of not
> knowing substream in usermode make stuff interesting!

The substream/subdevice index is in the snd_pcm_info field, so you can
correlate the PCM with the controls from the control API.

snd_pcm_info_get_subdevice()

					Jaroslav

-- 
Jaroslav Kysela <perex@perex.cz>
Linux Kernel Sound Maintainer
ALSA Project; Red Hat, Inc.

Re: PCM extra attributes

[Vinod Koul]

On Thu, Jul 25, 2013 at 10:06:52AM +0200, Jaroslav Kysela wrote:
> Date 24.7.2013 19:09, Vinod Koul wrote:
> > Hey Takashi,
> > 
> > We were looking to find the substream index in the userspace for the device
> > opened (in case we support multiple substreams and mix them). Since we also
> > wanted to have some specific alsa controls for each substream the problem of not
> > knowing substream in usermode make stuff interesting!
> 
> The substream/subdevice index is in the snd_pcm_info field, so you can
> correlate the PCM with the controls from the control API.
> 
> snd_pcm_info_get_subdevice()
This looks intresting, Thanks Jarsolav and Raymond.

If I get snd_pcm_info after the stream has been created I should see the
subdevice and thus use alsa controls corrorsponding.

Let me test this, it should work

~Vinod