On Fri, Feb 26, 2016 at 07:18:06PM -0500, Michael Reed wrote: > Hello, > > I use OpenBSD on my laptop to listen to music, using an external DAC > (USB) at home and built-in audio elsewhere. > > In rc.conf.local I have > > # see http://thread.gmane.org/gmane.os.openbsd.misc/213373/focus=213377 > sndiod_flags=-m play -f rsnd/1 -f rsnd/0 > > with the intention of using rsnd/1 (USB DAC) when it's available, and rsnd/0 > (built-in audio) when it's not. However, this is what actually seems to > happen when the USB DAC isn't plugged in (see DEFAULTS section in sndio(7)): > > - audio program tries to connect to snd/0, which fails because it doesn't > exist (snd/0 is a sub-device of rsnd/1 (USB DAC), which isn't plugged in) > > - audio program then tries rsnd/0 (/dev/audio0), which works > > The trouble is that, as shown by the second bullet, sndiod(8) is being > completely bypassed if the USB DAC isn't plugged in: > > # fuser -u /dev/audio[0-2] # sndiod_flags=-m play -f rsnd/1 -f rsnd/0 > /dev/audio2: > /dev/audio1: > /dev/audio0: 18636(_mpd) > > If I set sndiod_flags to empty, then sndiod is no longer bypassed > > $ fuser -u /dev/audio[0-2] # sndiod_flags= > /dev/audio2: > /dev/audio1: 3291(_sndio) > /dev/audio0: > > but, of course, the USB DAC won't be used at all. > > With that said, I'm wondering if it's even possible to set up sndiod so that > (1) my USB audio device is always used when available and (2) sndiod isn't > bypassed > if the DAC isn't available. > > After reading various sndio/audio manual pages I'm still somewhat > confused, so any help would be much appreciated.
Your understanding is right; this is a sndiod limitation. We don't have the code yet to do what you want. One option would to patch libsndio to try more devices (how many?). A nicer approach would be to handle this in sndiod by allowing sub-devices (aka -s options) to change their device (aka -f option). The advantage of doing it in sndiod is that later this could happen dynamically (ex. unplug usb cable and programs migrate to another device).
