1.. zephyr:code-sample:: uac2-implicit-feedback
2   :name: USB Audio asynchronous implicit feedback sample
3   :relevant-api: usbd_api uac2_device i2s_interface
4
5   USB Audio 2 implicit feedback sample playing stereo and recording mono audio
6   on I2S interface.
7
8Overview
9********
10
11This sample demonstrates how to implement USB asynchronous bidirectional audio
12with implicit feedback. The host adjusts number of stereo samples sent for
13headphones playback based on the number of mono microphone samples received.
14
15Requirements
16************
17
18Target must be able to measure I2S block start (i.e. first sample from output
19buffer gets out) relative to USB SOF. The relative offset must be reported with
20single sample accuracy.
21
22This sample has been tested on :ref:`nrf5340dk_nrf5340`. While for actual audio
23experience it is necessary to connect external I2S ADC and I2S DAC, simple echo
24can be accomplished by shorting I2S data output with I2S data input.
25
26Theoretically it should be possible to obtain the timing information based on
27I2S and USB interrupts, but currently neither subsystem currently provides
28necessary timestamp information.
29
30Building and Running
31********************
32
33The code can be found in :zephyr_file:`samples/subsys/usb/uac2_implicit_feedback`.
34
35To build and flash the application:
36
37.. zephyr-app-commands::
38   :zephyr-app: samples/subsys/usb/uac2_implicit_feedback
39   :board: nrf5340dk/nrf5340/cpuapp
40   :goals: build flash
41   :compact:
42