I just got this chip off of e-bay like the rest of you and was disappointed to find that it's not working.
Well, it's now been a couple hours of reading the ALSA wiki and figuring out where to look in the source code, but I've finally got this chip working in .20 under Debian.
After sniffing USB data with Wireshark on a VirtualBox instance of WinXP, I noticed that config data was being sent from the host shortly after device enumeration.
This makes sense since it didn't work in Windows either until I installed the driver (so much for following USB audio standards?).
I can only assume that the drivers contain the default settings for the device to be usable.
Why the registers don't look like this on reset is beyond me, but whatever.
In usbaudio.c in the snd_usb_audio_probe function (somewhere in the vicinity of line 3500) you need to enable the "boot quirk" for this chip:
/* C-Media CM6206 / CM106-Like Sound Device */
if (id == USB_ID(0x0d8c, 0x0102)) {
if (snd_usb_cm106_boot_quirk(dev) < 0)
goto __err_val;
}
Looks like the chip needs some config parameters sent to it via HID which are already there courtesy of the Turtle Beach hack.
The register setup is outlined in the datasheet (I found it here: http://pdf1.alldatasheet.net/datasheet-pdf/view/158787/CMEDIA/CM106-L+.html) on page 21.
The key is to set b15 in register 0x02 so that we can get the output.
Hope that helps,
---Dan
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