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Multi-channel audio over USB anyone?

Question asked by Ed Sutter on May 1, 2020
Latest reply on May 8, 2020 by Ed Sutter

I'm working with the usb_device_audio_generator example on the MIMXRT1060-EVK.  As is, it works and I've been able to modify the audio data and the descriptor to change the PCM width and the audio bit rate; however, I have not had any luck getting multiple channels to work.  I can get the audio to actually come out and it is split across 2 channels, but somehow it seems the feed rate is not correct.  When I hook linux-ALSA up to it, I get buffer over/underruns.

 

In USB-HS Isochronous Audio, the packet rate is 8000 pkts per second, not fully understanding the entire flow yet, I would have assumed that I would be getting a USB-handler interrupt at that rate, but that's not what I see.  Seems to be closer to about a 800-900 interrupts per second rather than 8000.  I have not yet figured out if the data is buffered and pushed out by the USB hardware (which would explain why I don't need to be interrupted 8000 times per second) or if I am just doing something wrong.

 

Anyone working on anything like this?

I'm pretty new to this level of USB development, so any pointers on descriptor design sure would be appreciated. 

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