RP2040: Dual UAC2 Audio devices caused tud_audio_rx_done_pre_read_cb callbacks on audio_n_write

[HiFiPhile]

Discussed in https://github.com/hathach/tinyusb/discussions/2083

^{Originally posted by **mkarliner** May 26, 2023} ### Operating System MacOS ### Board Raspberry Pi Pico ### Firmware Based on UAC2 headset example, extended to have 2 UAC2_Headset devices The headset example works as expected. ### What happened ? I have two UAC2 devices running. - A device called 'L' acts as a microphone, sending data from an electret microphone (using the RPi microphone library) up to the Mac using audio_n_write. - The Mac runs sox, consuming the mic data and sending it to a wav file. Note the Mac is not outputting to either of the device's speaker channel. - The tud_audio_rx_done_pre_read_cb callback is triggered, despite no data being sent to the speaker channels. ### How to reproduce ? On Mac : sox -r 44100 -t coreaudio "VM Loop" -c 2 test.wav tud_audio_rx_done_pre_read_cb is triggered. zipfile attached. evidence.c is a redacted version of main.c for readability. interface enum and endpoint defs are as follows num { ITF_NUM_AUDIO1_CONTROL = 0, ITF_NUM_AUDIO1_STREAMING_SPK, ITF_NUM_AUDIO1_STREAMING_MIC, // ITF_NUM_CDC, // ITF_CDC_DATA, // ITF_NUM_AUDIO2_CONTROL , ITF_NUM_AUDIO2_CONTROL, ITF_NUM_AUDIO2_STREAMING_SPK, ITF_NUM_AUDIO2_STREAMING_MIC, ITF_NUM_TOTAL }; #define EPNUM_AUDIO1_IN 0x01 #define EPNUM_AUDIO1_OUT 0x01 #define EPNUM_AUDIO2_IN 0x02 #define EPNUM_AUDIO2_OUT 0x02 [evidence.zip](https://github.com/hathach/tinyusb/files/11574661/evidence.zip) ### Debug Log as txt file (LOG/CFG_TUSB_DEBUG=2) WWW2 Queue EP 02 with 388 bytes ... USBD Xfer Complete on EP 82 with 0 bytes AUDIO xfer callback Queue EP 82 with 0 bytes ... USBD Xfer Complete on EP 02 with 176 bytes AUDIO xfer callback WWW2 Queue EP 02 with 388 bytes ... USBD Xfer Complete on EP 82 with 0 bytes AUDIO xfer callback Queue EP 82 with 0 bytes ... USBD Setup Received 01 0B 00 00 04 00 00 00 Set Interface AUDIO control request Set itf: 4 - alt: 0 CLOSING Endpoint: 0x02 Set interface 4 alt 0 Queue EP 80 with 0 bytes ... USBD Xfer Complete on EP 82 with 0 bytes AUDIO xfer callback Queue EP 82 with 0 bytes ... USBD Xfer Complete on EP 80 with 0 bytes USBD Setup Received 01 0B 00 00 05 00 00 00 Set Interface AUDIO control request Set itf: 5 - alt: 0 CLOSING Endpoint: 0x82 Set interface 5 alt 0 Queue EP 80 with 0 bytes ... USBD Xfer Complete on EP 80 with 0 bytes ### Screenshots _No response_ ### I have checked existing issues, dicussion and documentation - [X] I confirm I have checked existing issues, dicussion and documentation.

[mkarliner]

Is there any more information I can give to help with resolving this issue?