Hi, The existing usb-audio v.2 gadget defines its EP OUT as asynchronous https://github.com/torvalds/linux/blob/master/drivers/usb/gadget/function/f_uac2.c#L276 , but does not define any feedback IN EP (which is against USB audio class 2.0 specs). Windows 10 USB audio class 2 driver requires presence of the feedback EP. By changing the EP OUT to adaptive (which in fact it is), we could fix the driver issue and windows plays through such device (RPi4) correctly now (linux/OSX already worked OK before). We will post a patch soon. RPi can now be used as an "intelligent" USB soundcard, allowing further processing in linux on RPi, before outputting to some final sound device. However, there are two clock domains involved - the host USB controller sending stream to the USB gadget, and the output soundcard of the gadget. While adaptive resampling is possible (jackd, PA do that), IMO the correct solution is going back to ASYNC EP OUT in the audio gadget and implementing a proper feedback EP. But the feedback EP needs input data. The whole chain behind the virtual capture alsa device defined by the gadget driver is clocked by the playback soundcard. May I ask for your opinions on possible options for 1) gathering the feedback data from the playback chain 2) passing the gathered samplerate-diff data to the gadget module for the feedback EP to send to the USB host A general solution would be very useful, at best without using alsa-lib defined PCM devices (e.g. Java still supports only hardware devices (hw:X), not PCM devices defined by alsa-lib). I very much appreciate your suggestions and help. Best regards, Pavel. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
