[alsa-devel] Possible message repeat

[Brent Weatherall]

Hello.  I sent this message previously before I solidified my membership to
the list and it seems my message never posted.  Here it is again.
 My apologies if did go through and I missed it.

I am new to audio development in Linux.  I have worked with user space
development with respect to UVC code and I have worked with specifying an
XU in UVC.  I wrote a user space driver/application to talk to a device
supporting the UVC XU in Linux.  I am trying to specify an extension to the
UAC specification and then write a user space driver/application to use the
extension when a device that supports it is available in Linux.  Pretty
much the same situation as I have already done with UVC XU.  Windows and
Mac code will follow, but right now I am only concerned with Linux.

Can anyone assist me with the best path forward for writing user space code
to use the XU I am going to define?  Meaning generically speaking how to
use UAC XU controls in ALSA.  I was looking for code samples that use the
audio.h header file interface, but after a day and a half I am coming to
conclusion that only kernel space uses audio.h and that I will need to go
through ALSA to accomplish my task.  Again, this will be user space code I
want distribute easily, with minimal dependencies.  Our code will be
apache licensed afterwards if possible, just like our UVC code was.  So any
work I do should be freely available to the community afterwards. **EDIT
FROM PREVIOUS MESSAGE**  After more searching, it appears that any XU
controls would be processed through usbmixer.c, but I don't see how to use
the code in usbmixer from user space.  And so far I can't tell what source
usbmixer resides in.  I downloaded the alsa-lib source in Fedora, but I
don't see that file.  Is this a Linux kernel file?  So far I am having lots
of trouble finding anything useful regarding audio XUs in Linux.  My
apologies if this should be simple.  Thank you in advance for
any assistance.

Best Regards,

Brent