[LAU] MOTU AVB discussion from LAC

[Fons Adriaensen]

On Fri, Mar 29, 2019 at 08:52:04PM -0700, Paul Davis wrote:

> > Why can't I tell ALSA to use only the first 2, 4 whatever channels of
> > the device? I can only open the device if all channels are connected. Is
> > this always like that or is that a limitation of MOTU's implementation?
> 
> ALSA doesn't work that way. You open a device. You tell it how many
> channels you want to use.

At least in mmap mode (which is what Jack uses), this doesn't seem
to be so. snd_pcm_hw_params_set_channels () returns an error for
any number of channels not equal to the actual available number.

It makes sense, access is exclusive anyway. The only consequence
is that apps should probably write zeros to any output channels 
they don't want to use. 

If an app needs only 2 channels and fails to use a card offering
more, that's a bug in the app, not in ALSA.

Ciao,

-- 
FA