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samples: subsys: libMP: Add audio example
Add example for audio with a pipeline consists of a dmic source, a gain transform and a i2s sink element. Signed-off-by: Michal Chvatal <[email protected]>
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‎samples/subsys/libmp/audio_example/CMakeLists.txt‎

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CMAKE_MINIMUM_REQUIRED (VERSION 3.20.0)
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find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
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project(audio_example)
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target_sources(app PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/dmic_gain_speaker.c)

‎samples/subsys/libmp/audio_example/Kconfig‎

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# Copyright 2024-2025 NXP
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# SPDX-License-Identifier: Apache-2.0
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source "Kconfig.zephyr"
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config CODEC_MASTER
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bool "Configure the selected codec device as a master device."
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default true
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config I2S_MASTER
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bool "Configure the selected I2S peripheral as a master device."
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default false

‎samples/subsys/libmp/audio_example/README.rst‎

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.. zephyr:code-sample:: samples/subsys/libmp/audio_example/dmic-gain-speaker
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:name: DMIC-Gain-Speaker Audio Pipeline
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Overview
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********
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This sample demonstrates audio processing. It creates a simple audio pipeline
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that captures audio from a digital microphone (DMIC), applies gain control, and
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outputs the processed audio through an I2S codec to a speaker.
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The sample showcases:
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* Digital microphone audio capture
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* Real-time audio gain processing
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* I2S codec audio output
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* Media pipeline creation and management
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Requirements
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************
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* A board with digital microphone (DMIC) support
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* A board with I2S support
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* Sufficient RAM for audio buffering
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* DMA support for audio operations
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This sample has been tested on mimxrt685_evk/mimxrt685s/cm33
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Building and Running
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********************
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This sample can be found under :zephyr_file:`samples/subsys/libmp/audio_example/dmic-gain-speaker`.
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For :zephyr:board:`mimxrt685_evk`, build this sample application with the following commands:
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.. zephyr-app-commands::
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:zephyr-app: samples/subsys/libmp/audio_example
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:board: mimxrt685_evk/mimxrt685s/cm33
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:goals: build flash
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:compact:
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Connect headphones or speakers to the audio output to hear the processed
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audio from the DMIC.
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Sample Output
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*************
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The application will start the audio pipeline and process audio in real-time.
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Check for any error messages during initialization:
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.. code-block:: console
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*** Booting Zephyr OS build ***
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[00:01:56.811,938] <inf> wolfson_wm8904: blk 512000
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[00:01:57.816,263] <inf> mp_zaud_dmic_src: Capture started
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Configuration Options
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*********************
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The sample supports the following configuration options:
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* **Gain Level**: Adjustable audio gain (0-1000 %), default is 90 %
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Devicetree Configuration
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************************
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The sample requires proper devicetree configuration for:
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* ``dmic_dev`` node label for dmic.
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* ``i2s_codec_tx`` node alias for i2s.
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* ``audio_codec`` node label for audio codec.
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Implementation Details
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**********************
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The sample creates a three-element pipeline:
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1. **DMIC Source** (``zaud_dmic_src``): Captures audio from digital microphone
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2. **Gain Transform** (``zaud_gain``): Applies configurable gain to audio signal
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3. **I2S Codec Sink** (``zaud_i2s_codec_sink``): Outputs processed audio
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The pipeline uses DMA-compatible memory slabs for efficient audio buffer management.
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The ``__nocache`` attribute ensures proper DMA operation by preventing cache
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coherency issues.

‎samples/subsys/libmp/audio_example/boards/mimxrt685_evk_mimxrt685s_cm33.conf‎

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#
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# Copyright 2025 NXP
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#
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# SPDX-License-Identifier: Apache-2.0
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#
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CONFIG_I3C=y
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CONFIG_AUDIO=y
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CONFIG_AUDIO_CODEC=y
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CONFIG_CODEC_MASTER=y
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CONFIG_I2S_MASTER=n

‎samples/subsys/libmp/audio_example/boards/mimxrt685_evk_mimxrt685s_cm33.overlay‎

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/*
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* Copyright 2025 NXP
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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/ {
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aliases {
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i2s-codec-rx = &i2s0;
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i2s-codec-tx = &i2s1;
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};
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};
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&i3c0 {
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status = "okay";
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};
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&i2s0 {
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status = "okay";
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};
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&i2s1 {
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status = "okay";
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};
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dmic_dev: &dmic0 {
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status = "okay";
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};

‎samples/subsys/libmp/audio_example/dmic_gain_speaker.c‎

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/*
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* Copyright 2025 NXP
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#include <zephyr/kernel.h>
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#include <zephyr/logging/log.h>
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#include <mp.h>
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LOG_MODULE_REGISTER(main);
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#define LOG_LEVEL LOG_LEVEL_DBG
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/*
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* WORKAROUND: Direct memory slab management in application code
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*
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* TODO: Normally, applications should not set this because they do not
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* need to know about the memory slab audio buffers implementation.
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*
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* The __nocache attribute ensures this memory is not cached, which is
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* required for DMA operations used by audio hardware.
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*/
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__nocache struct k_mem_slab mem_slab;
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int main()
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{
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int gain = 90; /* Set gain to 90% (0.9x amplification) */
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int ret = 0;
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/* Initialize built-in elements and plugins */
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mp_init();
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/* Create elements */
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MpElement *source = mp_element_factory_create("zaud_dmic_src", "dmic");
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if (source == NULL) {
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LOG_ERR("Failed to create dmic element");
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return 0;
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}
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MpElement *transform = mp_element_factory_create("zaud_gain", "gain");
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if (transform == NULL) {
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LOG_ERR("Failed to create gain element");
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return 0;
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}
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MpElement *sink = mp_element_factory_create("zaud_i2s_codec_sink", "speaker");
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if (sink == NULL) {
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LOG_ERR("Failed to create speaker element");
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return 0;
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}
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ret = mp_object_set_properties(MP_OBJECT(source), PROP_ZAUD_SRC_SLAB_PTR, &mem_slab,
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PROP_LIST_END);
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if (ret < 0) {
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LOG_ERR("Failed to set properties for dmic element");
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return 0;
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}
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ret = mp_object_set_properties(MP_OBJECT(transform), PROP_GAIN, &gain, PROP_LIST_END);
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if (ret < 0) {
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LOG_ERR("Failed to set properties for transform element");
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return 0;
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}
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ret = mp_object_set_properties(MP_OBJECT(sink), PROP_ZAUD_SINK_SLAB_PTR, &mem_slab,
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PROP_LIST_END);
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if (ret < 0) {
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LOG_ERR("Failed to set properties for speaker element");
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return 0;
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}
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/* Create a new pipeline */
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MpElement *pipeline = mp_pipeline_new("dmic_gain_speaker_pipeline");
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if (pipeline == NULL) {
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LOG_ERR("Failed to create pipeline");
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return 0;
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}
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/* Add elements to the pipeline - order does not matter */
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if (mp_bin_add(MP_BIN(pipeline), source, transform, sink, NULL) == false) {
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LOG_ERR("Failed to add elements");
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return 0;
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}
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/* Link elements together - order does matter */
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if (mp_element_link(source, transform, sink, NULL) == false) {
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LOG_ERR("Failed to link elements");
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return 0;
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}
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/* Start playing */
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if (mp_element_set_state(pipeline, MP_STATE_PLAYING) != MP_STATE_CHANGE_SUCCESS) {
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LOG_ERR("Failed to start pipeline");
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return 0;
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}
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/* Handle message from the pipeline */
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MpBus *bus = mp_element_get_bus(pipeline);
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/* Wait until an Error or an EOS - blocking */
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MpMessage *msg = mp_bus_pop_msg(bus, MP_MESSAGE_ERROR | MP_MESSAGE_EOS);
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if (msg != NULL) {
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switch (MP_MESSAGE_TYPE(msg)) {
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case MP_MESSAGE_ERROR:
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LOG_INF("Received ERROR from %s\n", msg->src->name);
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break;
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case MP_MESSAGE_EOS:
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LOG_INF("Received EOS from %s\n", msg->src->name);
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break;
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default:
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LOG_ERR("Unexpected message received from %s\n", msg->src->name);
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break;
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}
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}
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/* TODO: Stop the pipeline */
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return 0;
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}

‎samples/subsys/libmp/audio_example/prj.conf‎

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CONFIG_LOG=y
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CONFIG_HEAP_MEM_POOL_SIZE=20000
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CONFIG_MP=y
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CONFIG_MP_PLUGIN_ZAUD=y
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CONFIG_I2S=y
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CONFIG_AUDIO=y
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CONFIG_AUDIO_DMIC=y
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CONFIG_AUDIO_CODEC=y
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CONFIG_SHELL=y
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CONFIG_DEVICE_SHELL=y

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