LUFA audio example volume control

[ratsept]

As you requested on the AVRFreaks forum.

--->Hello,

This is my first post here and I hope I can get some help. I am
working on a USB device that will have to play back sound from the
computer over USB. That part works well based on the example code in
LUFA. The problem is that I want to have volume control external to
the computer. I would like to make the master volume control in the
computer control an external device connected to the AVR.

I am using USBkey and JtagICE mkII if that makes a difference.

I would like to get this system to work and later I will be porting
parts of it to ARM controllers for higher speed and quality (hardware
I2S). The volume control device will be a relay controlled resistor
ladder network.

I started with the LUFA example for audio output and added a feature
unit into the audio control interface. There were some problem but I
got the device to enumerate again like this. It is now once again
getting sound from the computer but it is not possible to use the
volume control feature unit. I set breakpoints in the
CALLBACK_Audio_Device_GetSetEndpointProperty but they are never
reached. Sometimes the sample rate is queried but never anything
else.

How can I make the computer understand that my device has volume
control (and mute) and it should use this by sending requests?

Thank you all for this very nice forum and a really big thanks to Dean
for a superb piece of software.

P.S. Best of luck to Dean in Norway.

---

I will try the fix in the SVN on Monday if I get time. I will start
university classes again this week so it could take a little time.