[alsa-devel] 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