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Isochronous endpoint: device busy

Question asked by James Q. on May 20, 2013
Latest reply on Sep 18, 2013 by rodrigues.luiz
Hello all,

I'm trying to get a demo to work with an isochronous endpoint (audio speaker). My starting point are the Discovery-F4 demos, with USB-FS library upgraded to V3.3.0. 

I cannot seem to get the device to work. It enumerates and I can see the AudioControl endpoint. Using libusb-1.0, I can claim the interface, but writing to the endpoint results in a 'device is busy' error message.

I have compared the current source code with that of the demos endlessly, and cannot understand where the problem might be. I took out all DAC/I2S related code, but other than that all the IRQ handlers are identical. 

Does anyone have any suggestions for how to debug this? Is there a very simple approach that I can start with (e.g. take out the DMA altogether), and then work incrementally?

Thanks!

isochronous_endpoint.zip (344 KB)
https://mega.co.nz/#!PRAywLyI!c1PT3EpXCg_-kow67NyJTwQn-bE5ODk-oJFvYb5MFig

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