I'm interested in this matter as well. All I've found so far is I2S for audio output and USB for audio input.
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Latest posts made by Felipe Duque
I2S stopped working on firmware 0.2.2 (b200)
After upgrading the firmware to 0.2.2 (b200), no audio device is listed with either arecord or aplay. I don't recall what my previous version was, but an I2S device used to be shown (both input and output).
I have enabled the I2S pins but still no device is listed.
Anyone facing the same issue? How to proceed?