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USB full duplex audio problem on FRDM-KL25Z

Question asked by Michael Kraft on Apr 23, 2017

Hi everybody!


I am using the frdmkl25z_usb_examples_usb_device_audio_generator_bm as a starting point to develop a full duplex USB audio interface on the FRDM-KL25Z evaluation board.


It wasn't a big deal to change the original example to a 48 kHz sampling rate and 16 bit samples in stereo. But then I got completely stuck setting up the audio-out endpoint and interface.


Attached is my descriptor file. While I am pretty confident that the USB descriptor is correct, I have no clue about the descriptor replica that has to be setup for the USB library to work - unluckily I couldn't find any documentation.


Could please someone with more knowledge about this USB implementation give me some hint!?


Here is also a printout of the USB BDT.


It shows that Interrupt In-Endpoint 0x81 (BD starting at 0x1ffff620) is never used (Volume is updated via EP 0) and that Isochronous In-Endpoint 0x82 is setup and used correctly (BD at 0x1ffff650).
Isochronous Out-Endpoint 0x02 (BD at 0x1ffff640) has been set, but for unknown reasons never starts to work. More, the out-ep does not cause any USB Interrupts, while the working in-ep does nicely every 1 ms.


Any help is welcome!



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