Finding PCM audio devices in C/C++ on the BeagleBone Black (and other embedded Linux systems)

Finding PCM audio devices using the ALSA interface from software isn’t always completely trivial. On some builds for the BeagleBone Black, PCM audio devices appear as /dev/audio, /dev/audio1 etc. But this doesn’t seem to be generally true. Plus, this doesn’t definitively identify which device is which. A good way to find out is to open the pseudo file /proc/asound/pcm as it lists all the PCM devices in the system. To see what’s currently active, just cat the pseudo file:

UbuntuDev$ cat /proc/asound/pcm
 00-00: ALC889 Analog : ALC889 Analog : playback 1 : capture 1
 00-01: ALC889 Digital : ALC889 Digital : playback 1
 00-02: ALC889 Analog : ALC889 Analog : capture 2
 00-03: HDMI 0 : HDMI 0 : playback 1
 01-00: USB Audio : USB Audio : capture 1
 02-03: HDMI 0 : HDMI 0 : playback 1
 02-07: HDMI 0 : HDMI 0 : playback 1
 02-08: HDMI 0 : HDMI 0 : playback 1
 02-09: HDMI 0 : HDMI 0 : playback 1

The first two numbers are the plughw card and device numbers. So, if you wanted to connect to the USB audio source for example, you could do:

snd_pcm_open (&m_handle, "plughw:1,0", SND_PCM_STREAM_CAPTURE, 0);