[linux-audio-user] USX2Y rawusb mode

[Karsten Wiese]

Am Donnerstag 03 März 2005 13:41 schrieb Rui Nuno Capela:
> Karsten,
> 
> >
> > 1. Patch jack's alsa driver, compile and install it:
> >  >>>>>>>
> > --- alsa_driver.c.~1.65.~       2005-02-22 01:15:07.000000000 +0100
> > +++ alsa_driver.c       2005-02-22 01:16:32.000000000 +0100
> > @@ -450,7 +450,7 @@
> >         }
> >
> >         if ((err = snd_pcm_hw_params_set_channels (handle, hw_params,
> > -                                                  *nchns)) < 0) {
> > +                                                  2 /* *nchns*/)) < 0) {
> >                 jack_error ("ALSA: cannot set channel count to %u for %s",
> >                             *nchns, stream_name);
> >                 return -1;
> > <<<<<<<
> > 2.
> > 	$ modprobe snd_usb_usx2y nrpacks=1
> > 3.
> > 	$ jackd -R -dalsa -dhw:0,2
> >
> 
> I once asked if this patch is really necessary. I think, but not sure (as
> I gave no us428 here), it is quite equivalent to start jackd explicitly
> with -i2 -o2 arguments.
> 
> Am I wrong?

partly. with -i2 us428 will use 2 in channels, but we want all 4.
without that option or with -i4 and
	without patch
		4 in channels but nothing is usable: sounds awful
	with patch
		4 in channels and works

The patch is needed to make alsa think that jackd wants only 2 in channels,
while jackd actually works with 4 in channels.
For us428 snd-usb-usx2y correctly reports "I have 4 in channels"
but there is still something wrong (in snd-usb-usx2y raw usb mode: have put some hours in it already without success)
that makes it necessary to cheat alsa a little for the us428 4in channels case.

cheers