[LAU] MOTU AVB discussion from LAC

[Max]

On 30.03.19 09:28, Fons Adriaensen wrote:
> 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.

Makes sense. My thinking was that I could possibly get lower latency and
less overhead if I only acquire two or four channels instead of 24 or 64 
from which I leave the majority idle... But I understand its just now 
how ALSA was designed.