atlury / nrf5340-audio-4-channels

nRF5340 Audio

• Overview
  • Application modes
  • Firmware architecture
• Requirements
  • Software codec requirements
  • nRF5340 Audio development kit
  • nRF5340 Audio configuration files
  • Requirements for FOTA
• User interface
  • Switches
  • Buttons
  • LEDs
• Configuration
  • Selecting the BIS mode
  • Selecting the I2S serial
  • Configuring FOTA upgrades
• Building and running
  • Testing out of the box
  • Building and programming using script
  • Building and programming using command line
  • Testing
• Adapting application for end products
  • Board configuration sources
  • Application configuration sources
  • Adding a new board
  • FOTA for end products
• Dependencies
• Application configuration options
• Legal notices and disclaimers

The nRF5340 Audio application demonstrates audio playback over isochronous channels (ISO) using LC3 codec compression and decompression, as per `Bluetooth® LE Audio specifications`_. It is developed for use with the :ref:`nrf53_audio_app_dk`.

In its default configuration, the application requires the :ref:`LC3 software codec <nrfxlib:lc3>`. The application also comes with various tools, including the :file:`buildprog.py` Python script that simplifies building and programming the firmware.

Overview

The application can work as a gateway or a headset. The gateway receives the audio data from external sources (USB or I2S) and forwards it to one or more headsets. The headset is a receiver device that plays back the audio it gets from the gateway.

Both device types use the same code base, but different firmware, and you need both types of devices for testing the application. Gateways and headsets can both run in one of the available application modes, either the connected isochronous stream (CIS) mode or in the broadcast isochronous stream (BIS) mode. The CIS mode is the default mode of the application.

Changing configuration related to the device type and the application modes requires rebuilding the firmware and reprogramming the development kits.

Regardless of the configuration, the application handles the audio data in the following manner:

1. The gateway receives audio data from the audio source over USB or I2S.
2. The gateway processes the audio data in its application core, which channels the data through the application layers:
   1. Audio data is sent to the synchronization module (I2S-based firmware) or directly to the software codec (USB-based firmware).
   2. Audio data is encoded by the software codec.
   3. Encoded audio data is sent to the Bluetooth LE Host.
3. The host sends the encoded audio data to the LE Audio Controller Subsystem for nRF53 on the network core.
4. The subsystem forwards the audio data to the hardware radio and sends it to the headset devices, as per the LE Audio specifications.
5. The headsets receive the encoded audio data on their hardware radio on the network core side.
6. The LE Audio Controller Subsystem for nRF53 running on each of the headsets sends the encoded audio data to the Bluetooth LE Host on the headsets' application core.
7. The headsets process the audio data in their application cores, which channel the data through the application layers:
   1. Audio data is sent to the stream control module and placed in a FIFO buffer.
   2. Audio data is sent from the FIFO buffer to the synchronization module (headsets only use I2S-based firmware).
   3. Audio data is decoded by the software codec.
8. Decoded audio data is sent to the hardware audio output over I2S.

Note

Currently, only a unidirectional stream is supported (gateway to headsets). In addition, only the gateway uses USB. This means that no decoded audio data is sent over USB in the current version.

In the I2S-based firmware for gateway and headsets, sending the audio data through the application layers includes a mandatory synchronization step using the synchronization module. This proprietary module ensures that the audio is played at the same time with the correct speed. For more information, see Synchronization module overview.

Application modes

The application can work either in the connected isochronous stream (CIS) mode or in the broadcast isochronous stream (BIS) mode, depending on the chosen firmware configuration.

CIS and BIS mode overview

Connected Isochronous Stream (CIS)

CIS is a bidirectional communication protocol that allows for sending separate connected audio streams from a source device to one or more receivers. The gateway can send the audio data using both the left and the right ISO channels at the same time, allowing for stereophonic sound reproduction with synchronized playback.

This is the default configuration of the nRF5340 Audio application. In this configuration, you can use the nRF5340 Audio development kit in the role of the gateway, the left headset, or the right headset.

Note

In the current version of the nRF5340 Audio application, the CIS mode offers only monodirectional communication.

Broadcast Isochronous Stream (BIS)

BIS is a monodirectional communication protocol that allows for broadcasting one or more audio streams from a source device to an unlimited number of receivers that are not connected to the source.

In this configuration, you can use the nRF5340 Audio development kit in the role of the gateway or as one of the headsets. Use multiple nRF5340 Audio development kits to test BIS having multiple receiving headsets.

Note

• In the BIS mode, you can use any number of nRF5340 Audio development kits as receivers.
• In the current version of the nRF5340 Audio application, the BIS mode offers only monophonic sound reproduction.

The audio quality for both modes does not change, although the processing time for stereo can be longer.

Firmware architecture

The following figure illustrates the software layout for the nRF5340 Audio application:

nRF5340 Audio high-level design (overview)

The network core of the nRF5340 SoC runs the LE Audio Controller Subsystem for nRF53. This subsystem is a Bluetooth LE Controller that is custom-made for the application. It is responsible for receiving the audio stream data from hardware layers and forwarding the data to the Bluetooth LE host on the application core. The subsystem implements the lower layers of the Bluetooth Low Energy software stack and follows the LE Audio specification requirements.

The application core runs both the Bluetooth LE Host from Zephyr and the application layer. The application layer is composed of a series of modules from different sources. These modules include the following major ones:

• Peripheral modules from the |NCS|:

  • I2S
  • USB
  • SPI
  • TWI/I2C
  • UART (debug)
  • Timer
  • LC3 encoder/decoder

• Application-specific Bluetooth modules for handling the Bluetooth connection:

  • :file:`le_audio_cis_gateway.c` or :file:`le_audio_cis_headset.c` - One of these cis modules is used by default.
  • :file:`le_audio_bis_gateway.c` or :file:`le_audio_bis_headset.c` - One of these bis modules is selected automatically when you :ref:`switch to the BIS configuration <nrf53_audio_app_configuration_select_bis>`.

  Only one of these files is used at compile time. Each of these files handles the Bluetooth connection and Bluetooth events and funnels the data to the relevant audio modules.

• Application-specific custom modules:

  • Stream Control - This module implements a simple state machine for the application (STREAMING or PAUSED). It also handles events from Bluetooth LE and buttons, receives audio from the host, and forwards the audio data to the next module.
  • FIFO buffers
  • Synchronization module (part of I2S-based firmware for gateway and headsets) - See Synchronization module overview for more information.

Since the application architecture is uniform and the firmware code is shared, the set of audio modules in use depends on the chosen stream mode (BIS or CIS), the chosen audio inputs and outputs (USB or analog jack), and if the gateway or the headset configuration is selected.

Note

In the current version of the application, the bootloader is disabled by default. Device Firmware Update (DFU) can only be enabled when :ref:`nrf53_audio_app_building_script`. See :ref:`nrf53_audio_app_configuration_configure_fota` for details.

USB-based firmware for gateway

The following figure shows an overview of the modules currently included in the firmware that uses USB:

nRF5340 Audio modules on the gateway using USB

In this firmware design, no synchronization module is used after decoding the incoming frames or before encoding the outgoing ones. The Bluetooth LE RX FIFO is mainly used to make decoding run in a separate thread.

I2S-based firmware for gateway and headsets

The following figure shows an overview of the modules currently included in the firmware that uses I2S:

nRF5340 Audio modules on the gateway and the headsets using I2S

The Bluetooth LE RX FIFO is mainly used to make :file:`audio_datapath.c` (synchronization module) run in a separate thread. After encoding the audio data received from I2S, the frames are sent by the encoder thread using a function located in :file:`streamctrl.c`.

Synchronization module overview

The synchronization module (:file:`audio_datapath.c`) handles audio synchronization. To synchronize the audio, it executes the following types of adjustments:

• Presentation compensation
• Drift compensation

The presentation compensation makes all the headsets play audio at the same time, even if the packets containing the audio frames are not received at the same time on the different headsets. In practice, it moves the audio data blocks in the FIFO forward or backward a few blocks, adding blocks of silence when needed.

The drift compensation adjusts the frequency of the audio clock to adjust the speed at which the audio is played. This is required in the CIS mode, where the gateway and headsets must keep the audio playback synchronized to provide True Wireless Stereo (TWS) audio playback. As such, it provides both larger adjustments at the start and then continuous small adjustments to the audio synchronization. This compensation method counters any drift caused by the differences in the frequencies of the quartz crystal oscillators used in the development kits. Development kits use quartz crystal oscillators to generate a stable clock frequency. However, the frequency of these crystals always slightly differs. The drift compensation makes the inter-IC sound (I2S) interface on the headsets run as fast as the Bluetooth packets reception. This prevents I2S overruns or underruns, both in the CIS mode and the BIS mode.

See the following figure for an overview of the synchronization module.

nRF5340 Audio synchronization module overview

Both synchronization methods use the SDU reference timestamps (:c:type:`sdu_ref`) as the reference variable. If the device is a gateway that is :ref:`using I2S as audio source <nrf53_audio_app_overview_architecture_i2s>` and the stream is unidirectional (gateway to headsets), :c:type:`sdu_ref` is continuously being extracted from the LE Audio Controller Subsystem for nRF53 on the gateway. The extraction happens inside the :file:`le_audio_cis_gateway.c` and :file:`le_audio_bis_gateway.c` files' send function. The :c:type:`sdu_ref` values are then sent to the gateway's synchronization module, and used to do drift compensation.

Note

Inside the synchronization module (:file:`audio_datapath.c`), all time-related variables end with _us (for microseconds). This means that :c:type:`sdu_ref` becomes :c:type:`sdu_ref_us` inside the module.

As the nRF5340 is a dual-core SoC, and both cores need the same concept of time, each core runs a free-running timer in an infinite loop. These two timers are reset at the same time, and they run from the same clock source. This means that they should always show the same values for the same points in time. The network core of the nRF5340 running the LE controller for nRF53 uses its timer to generate the :c:type:`sdu_ref` timestamp for every audio packet received. The application core running the nRF5340 Audio application uses its timer to generate :c:type:`cur_time` and :c:type:`frame_start_ts`.

After the decoding takes place, the audio data is divided into smaller blocks and added to a FIFO. These blocks are then continuously being fed to I2S, block by block.

See the following figure for the details of the compensation methods of the synchronization module.

nRF5340 Audio's state machine for compensation mechanisms

The following external factors can affect the presentation compensation:

• The drift compensation must be synchronized to the locked state (:c:enumerator:`DRIFT_STATE_LOCKED`) before the presentation compensation can start. This drift compensation adjusts the frequency of the audio clock, indicating that the audio is being played at the right speed. When the drift compensation is not in the locked state, the presentation compensation does not leave the init state (:c:enumerator:`PRES_STATE_INIT`). Also, if the drift compensation loses synchronization, moving out of :c:enumerator:`DRIFT_STATE_LOCKED`, the presentation compensation moves back to :c:enumerator:`PRES_STATE_INIT`.
• When audio is being played, it is expected that a new audio frame is received in each ISO connection interval. If this does not occur, the headset might have lost its connection with the gateway. When the connection is restored, the application receives a :c:type:`sdu_ref` not consecutive with the previously received :c:type:`sdu_ref`. Then the presentation compensation is put into :c:enumerator:`PRES_STATE_WAIT` to ensure that the audio is still in sync.

Note

When both the drift and presentation compensation are in state locked (:c:enumerator:`DRIFT_STATE_LOCKED` and :c:enumerator:`PRES_STATE_LOCKED`), LED2 lights up.

Synchronization module flow

The received audio data in the I2S-based firmware devices follows the following path:

1. The LE Audio Controller Subsystem for nRF53 running on the network core receives the compressed audio data.
2. The controller subsystem sends the audio data to the Zephyr Bluetooth LE host similarly to the :ref:`zephyr:bluetooth-hci-rpmsg-sample` sample.
3. The host sends the data to the stream control module (:file:`streamctrl.c`).
4. The data is sent to a FIFO buffer.
5. The data is sent from the FIFO buffer to the :file:`audio_datapath.c` synchronization module. The :file:`audio_datapath.c` module performs the audio synchronization based on the SDU reference timestamps. Each package sent from the gateway gets a unique SDU reference timestamp. These timestamps are generated on the headset controllers (in the network core). This enables the creation of True Wireless Stereo (TWS) earbuds where the audio is synchronized in the CIS mode. It does also keep the speed of the inter-IC sound (I2S) interface synchronized with the sending and receiving speed of Bluetooth packets.
6. The :file:`audio_datapath.c` module sends the compressed audio data to the LC3 audio decoder for decoding.
7. The audio decoder decodes the data and sends the uncompressed audio data (PCM) back to the :file:`audio_datapath.c` module.
8. The :file:`audio_datapath.c` module continuously feeds the uncompressed audio data to the hardware codec.
9. The hardware codec receives the uncompressed audio data over the inter-IC sound (I2S) interface and performs the digital-to-analog (DAC) conversion to an analog audio signal.

Requirements

The nRF5340 Audio application is designed to be used only with the following hardware:

Hardware platforms	PCA	Board name	Build target
nRF5340 Audio DK	PCA10121 revision 1.0.0 or above	nrf5340_audio_dk_nrf5340	nrf5340_audio_dk_nrf5340_cpuapp

Note

The application supports PCA10121 revisions 1.0.0 or above. The application is also compatible with the following pre-launch revisions:

• Revision 0.7.0 (not recommended).
• Revisions 0.8.0 and above.

You need at least two nRF5340 Audio development kits (one with the gateway firmware and one with headset firmware) to test the application. For CIS with TWS in mind, three kits are required.

Software codec requirements

The nRF5340 Audio application only supports the :ref:`LC3 software codec <nrfxlib:lc3>`, developed specifically for use with LE Audio.

nRF5340 Audio development kit

The nRF5340 Audio development kit is a hardware development platform that demonstrates the nRF5340 Audio application.

Key features of the nRF5340 Audio DK

• Nordic Semiconductor's nRF5340 Bluetooth LE / multiprotocol SoC.

• Nordic Semiconductor's nPM1100 power management SoC.

• CS47L63 AD-DA converter from Cirrus Logic, dedicated to TWS devices.

• Stereo analog line input.

• Mono analog output.

• Onboard Pulse Density Modulation (PDM) microphone.

• Computer connection and battery charging through USB-C.

• Second nRF5340 SoC that works as an onboard SEGGER debugger.

• SD card reader (no SD card supplied).

• User-programmable buttons and LEDs.

• Normal operating temperature range 10–40°C.

  Note

  The battery supplied with this kit can operate with a max temperature of Max +60°C.

• When using a power adapter to USB, the power supply adapter must meet USB power supply requirements.

• Embedded battery charge system.

• Rechargeable Li-Po battery with 1500 mAh capacity.

Hardware drawings

The nRF5340 Audio hardware drawings show both sides of the development kit in its plastic case:

Figure 1. nRF5340 Audio DK (PCA10121) front view

Figure 2. nRF5340 Audio DK (PCA10121) back view

The following figure shows the back of the development kit without the case:

Figure 3. nRF5340 Audio DK (PCA10121) back view without case

For the description of the relevant PCB elements, see the User interface section.

Solder bridge overview

The nRF5340 Audio DK has a range of solder bridges for enabling or disabling selected functionalities. Changes to these are not needed for normal use of the DK. The following table is a complete overview of the solder bridges on the nRF5340 Audio DK.

Designator	Description	Default state	Layer
SB1	Short to connect digital microphone DOUT to P1.06	Open	Top
SB2	Cut to disconnect P0.12 from TRACE	Shorted	Top
SB3	Short to connect PMIC MODE to VOUTB, must not be shorted while SB4 is shorted	Open	Top
SB4	Cut to disable PMIC MODE from GND, must not be shorted while SB3 is shorted	Shorted	Top
SB5	Cut to enable VBAT current measurements on P6	Shorted	Top
SB6	Cut to enable HW CODEC 1.2V current measurements on P7	Shorted	Top
SB7	Cut to enable HW CODEC 1.8V current measurements on P8	Shorted	Top
SB8	Cut to enable VDD_nRF current measurements on P9	Shorted	Top
SB9	Cut to disconnect filter from OUTP	Shorted	Top
SB10	Cut to disconnect filter from OUTN	Shorted	Top
SB11	Cut to disconnect the LED for the HW CODEC GPIO	Shorted	Top
SB12	Cut to disconnect digital microphone POWER from the HW CODEC	Shorted	Bottom
SB13	Cut to disconnect digital microphone DATA from the HW CODEC	Shorted	Bottom
SB14	Cut to disconnect digital microphone CLOCK from the HW CODEC	Shorted	Bottom
SB15	Short to connect AUX I2S MCLK to HW CODEC MCLK1	Open	Top
SB16	Short to connect AUX I2S MCLK to HW CODEC MCLK2	Open	Top
SB17	Short to connect P5 pin 6 to GND	Open	Top
SB18	Cut to disconnect P5 pin 6 from SHIELD DETECT	Shorted	Top
SB19	Cut to disconnect RTS and CTS flow control lines on UART1	Shorted	Top
SB20	Cut to disconnect RTS and CTS flow control lines on UART2	Shorted	Top
SB21	Cut to disconnect nRF53 RESET from RESET button when debug is disabled	Shorted	Top
SB22	Short to permanently connect RESET button to nRF53 RESET	Open	Top
SB23	Cut to disconnect RESET button from interface MCU	Shorted	Top
SB24	Short to bypass analog switch for MCLK	Open	Top

Testpoint overview

The following table is a complete overview of the test points on the nRF5340 Audio DK.

Designator	Net	Description	Size	Layer
TP1	NetTP1-1	IN1LP_1 pin of CS47L63	1.5mm	Bottom
TP2	NetTP2-1	IN1LN_1 pin of CS47L63	1.5mm	Bottom
TP3	NetTP3-1	IN1RP pin of CS47L63	1.5mm	Bottom
TP4	NetTP4-1	IN1RN pin of CS47L63	1.5mm	Bottom
TP5	NetTP5-1	IN2LN pin of CS47L63	1.5mm	Bottom
TP6	NetTP6-1	IN2RN pin of CS47L63	1.5mm	Bottom
TP7	HW_CODEC_AUX_I2C.SCL	AUX SCL pin of CS47L63	1.5mm	Top
TP8	HW_CODEC_AUX_I2C.SDA	AUX SDA pin of CS47L63	1.5mm	Top
TP9	P0.07/AIN3	RGB LED 1 Red color input pin	1.5mm	Top
TP10	P0.28/AIN7	RGB LED 2 Red color input pin	1.5mm	Top
TP11	P1.01	LED 3 input pin	1.5mm	Top
TP12	P0.04/AIN0	Button 3	1.5mm	Top
TP13	VDD_EXT_HW_CODEC.1V2	External HW CODEC 1.2V supply	1.5mm	Top
TP14	VDD_EXT_HW_CODEC.1V8	External HW CODEC 1.8V supply	1.5mm	Top
TP15	BAT_NTC	Li-poly battery NTC pin	1.5mm	Top
TP16	BATTERY	Li-poly battery voltage after power switch	1.5mm	Top
TP17	NetC41-1	USB voltage after power switch	1.5mm	Top
TP18	NetC43-2	USB voltage before power switch	1.5mm	Top
TP19	HEADPHONE.OUTP	Headphone jack tip	1.5mm	Top
TP20	HEADPHONE.OUTN	Headphone jack sleeve	1.5mm	Top
TP21	DU_N	USB connector D-	1.5mm	Top
TP22	DU_P	USB connector D+	1.5mm	Top
TP23	SWDIO	nRF5340 Serial Wire Debug data	1.5mm	Top
TP24	SWDCLK	nRF5340 Serial Wire Debug clock	1.5mm	Top
TP25	RESET	nRF5340 Reset	1.5mm	Top
TP26	SD_CS	SD card slot CS line	1.5mm	Top
TP27	SD_SCK	SD card slot SCK line	1.5mm	Top
TP28	VDD_IN_1V	1.2V regulator output	1.5mm	Top
TP29	SUPPLY_1V8	nPM1100 1.8V output	1.5mm	Top
TP30	SUPPLY_3V3	3.3V regulator output	1.5mm	Top
TP31	VDD_DBG_3V3	Debug regulator 3.3V output	1.5mm	Top
TP32	VDD_DBG_1V8	Debug regulator 1.8V output	1.5mm	Top
TP33	SW_EN	Load switch enable signal	1.5mm	Top
TP34	GND	Ground	1.5mm	Top
TP35	GND	Ground	1.5mm	Top
TP36	NetQ9-1	Debug enable signal	1.5mm	Top
TP37	IMCU_SWDIO	Interface MCU Serial Wire Debug data	1.5mm	Top
TP38	IMCU_RESET	Interface MCU Reset	1.5mm	Top
TP39	IMCU_SWDCLK	Interface MCU Serial Wire Debug clock	1.5mm	Top
TP40	SHIELD_DETECT	Detect signal for Arduino compatible shield	1.0mm	Top
TP41	HW_CODEC_IF.SPI.MISO	SPI MISO pin of CS47L63	1.0mm	Top
TP42	HW_CODEC_IF.SPI.MOSI	SPI MOSI pin of CS47L63	1.0mm	Top
TP43	HW_CODEC_IF.SPI.SCK	SPI SCK pin of CS47L63	1.0mm	Top
TP44	HW_CODEC_IF.SPI.CS	SPI SS pin of CS47L63	1.0mm	Top
TP45	HW_CODEC_IF.CTRL.GPIO	GPIO pin of CS47L63	1.0mm	Top
TP46	HW_CODEC_IF.CTRL.IRQ	IRQ pin of CS47L63	1.0mm	Top
TP47	HW_CODEC_IF.CTRL.RESET	RESET pin of CS47L63	1.0mm	Top
TP48	HW_CODEC_IF.I2S.MCLK	MCLK1 pin of CS47L63	1.0mm	Top
TP49	HW_CODEC_IF.I2S.DOUT	I2S DOUT pin of CS47L63	1.0mm	Top
TP50	HW_CODEC_IF.I2S.DIN	I2S DIN pin of CS47L63	1.0mm	Top
TP51	HW_CODEC_IF.I2S.BCLK	I2S BCLK pin of CS47L63	1.0mm	Top
TP52	HW_CODEC_IF.I2S.FSYNC	I2S FSYNC pin of CS47L63	1.0mm	Top
TP53	NetSB12-1	MICBIASB pin of CS47L63	1.0mm	Top
TP54	NetSB13-1	IN1_PDMDATA pin of CS47L63	1.0mm	Top
TP55	NetSB14-1	IN1_PDMCLK pin of CS47L6	1.0mm	Top
TP56	PMIC_ERR	nPM1100 error indication	1.0mm	Top
TP57	PMIC_CHG	nPM1100 charge indication	1.0mm	Top
TP58	P0.29	RGB LED 2 Green color input pin	1.0mm	Top
TP59	P0.30	RGB LED 2 Blue color input pin	1.0mm	Top
TP60	P1.04	UART1 RXD	1.0mm	Top
TP61	P1.05	UART1 TXD	1.0mm	Top
TP62	P1.06	UART1 CTS	1.0mm	Top
TP63	P1.07	UART1 RTS	1.0mm	Top
TP64	NetJ5-10	SD card slot card detect	1.0mm	Top
TP65	P0.11	SD card slot level translator enable	1.0mm	Top
TP66	P1.15	Current shunt monitor alert signal	1.0mm	Top
TP67	GND	Ground	1.5mm	Top
TP68	LINE_IN.LEFT	Line-in jack tip	1.5mm	Top
TP69	LINE_IN.RIGHT	Line-in jack ring	1.5mm	Top

nRF5340 Audio hardware limitations

The following table lists hardware limitations discovered in different revisions of the nRF5340 Audio DK.

PCA10121 revision	Limitation	Description	Workaround	Fixed in revision
Rev 1.0.0	CS47L63 AD-DA converter (U2) may fail to start	In some occasions, the 1.2 V power supply for U2 is not provided at boot-up. This is caused by higher than expected inrush current. This function is tested in production. The issue should not happen, although we observe that some kits have the problem.	Restart kit or attach the battery to the kit before connecting the USB cable. If problem persists, contact Nordic Semiconductor and ask for replacement.	Rev 1.0.1

nRF5340 Audio configuration files

The nRF5340 Audio application uses :file:`Kconfig.defaults` files to change configuration defaults automatically, based on the different application versions and device types.

Only one of the following :file:`.conf` files is included when building:

• :file:`prj.conf` is the default configuration file and it implements the debug application version.
• :file:`prj_release.conf` is the optional configuration file and it implements the release application version. No debug features are enabled in the release application version. When building using the command line, you must explicitly specify if :file:`prj_release.conf` is going to be included instead of :file:`prj.conf`. See :ref:`nrf53_audio_app_building` for details.

Requirements for FOTA

To test Firmware Over-The-Air (FOTA), you need an Android or iOS device with the `nRF Connect Device Manager`_ app installed.

If you want to do FOTA upgrades for the application core and the network core at the same time, you need an external flash shield. See :ref:`nrf53_audio_app_configuration_configure_fota` for more details.

User interface

The application implements a simple user interface based on the available PCB elements. You can control the application using predefined switches and buttons while the LEDs display information.

Switches

The application uses the following switches on the supported development kit:

Switch	Function
POWER	Turns the development kit on or off.
DEBUG ENABLE	Turns on or off power for debug features. This switch is used for accurate power and current measurements.

Buttons

The application uses the following buttons on the supported development kit:

Button	Function
VOL-	Turns the playback volume down (and unmutes).
VOL+	Turns the playback volume up (and unmutes).
PLAY/PAUSE	Starts or pauses the playback.
BTN 4	Depending on the moment it is pressed: Long-pressed during startup: Turns on the DFU mode, if the device is :ref:`configured <nrf53_audio_app_configuration_configure_fota>`. Pressed on the gateway during playback: Sends a test tone generated on the device. Use this tone to check the synchronization of headsets. Pressed on the gateway during playback multiple times: Changes the tone frequency. The available values are 1000 Hz, 2000 Hz, and 4000 Hz.
BTN 5	Depending on the moment it is pressed: Long-pressed during startup: Clears the previously stored bonding information. Pressed during playback: Mutes the playback volume.
RESET	Resets the device.

LEDs

To indicate the tasks performed, the application uses the LED behavior described in the following table:

LED	Indication
LED1	Off - No Bluetooth connection.
	Blinking blue - Depending on the device and the mode: Headset: Kits have started streaming audio (BIS and CIS modes). Gateway: Kit has connected to a headset (CIS mode) or has started broadcasting audio (BIS mode).
	Solid blue - Headset, depending on the mode: Kits have connected to the gateway (CIS mode) or found a broadcasting stream (BIS mode).
LED2	Off - Sync not achieved.
	Solid green - Sync achieved (both drift and presentation compensation are in the LOCKED state).
LED3	Blinking green - The nRF5340 Audio DK application core is running.
CODEC	Off - No configuration loaded to the onboard hardware codec.
	Solid green - Hardware codec configuration loaded.
RGB1 (bottom side LEDs around the center opening)	Solid green - The device is programmed as the gateway.
	Solid blue - The device is programmed as the left headset.
	Solid magenta - The device is programmed as the right headset.
	Solid yellow - The device is programmed with factory firmware. It must be re-programmed as gateway or headset.
	Solid red (debug mode) - Fault in the application core has occurred. See UART log for details and use the RESET button to reset the device. In the release mode, the device resets automatically with no indication on LED or UART.
RGB 2	Controlled by the Bluetooth LE Controller on the network core.
	Blinking green - Ongoing CPU activity.
	Solid red - Error.
	Solid white (all colors on) - The RGB 2 LED is not initialized by the Bluetooth LE Controller.
ERR	PMIC error or a charging error (or both).
CHG	Off - Charge completed or no battery connected.
	Solid yellow - Charging in progress.
OB/EXT	Off - No 3.3 V power available.
	Solid green - On-board hardware codec selected.
	Solid yellow - External hardware codec selected. This LED turns solid yellow also when the devices are reset, for the time then pins are floating.
FTDI SPI	Off - No data is written to the hardware codec using SPI.
	Yellow - The same SPI is used for both the hardware codec and the SD card. When this LED is yellow, the shared SPI is used by the FTDI to write data to the hardware codec.
IFMCU (bottom side)	Off - No PC connection available.
	Solid green - Connected to PC.
	Rapid green flash - USB enumeration failed.
HUB (bottom side)	Off - No PC connection available.
	Green - Standard USB hub operation.

Configuration

|config|

Selecting the BIS mode

The CIS mode is the default operating mode for the application. You can switch to the BIS mode by adding the CONFIG_TRANSPORT_BIS Kconfig option set to y to the :file:`prj.conf` file for the debug version and the :file:`prj_release.conf` file for the release version.

Selecting the I2S serial

In the default configuration, the gateway application uses the USB serial port as the audio source. The :ref:`nrf53_audio_app_building` and :ref:`nrf53_audio_app_testing` steps also refer to using the USB serial connection.

You can switch to using the I2S serial connection by adding the CONFIG_AUDIO_SOURCE_I2S Kconfig option set to y to the :file:`prj.conf` file for the debug version and the :file:`prj_release.conf` file for the release version.

When testing the application, an additional audio jack cable is required to use I2S. Use this cable to connect the audio source (PC) to the analog LINE IN on the development kit.

Configuring FOTA upgrades

Caution!

Firmware based on the |NCS| versions earlier than v2.1.0 does not support DFU. FOTA is not available for those versions.

You can test performing separate application and network core upgrades, but for production, both cores must be updated at the same time. When updates take place in the inter-core communication module (HCI RPMsg), communication between the cores will break if they are not updated together.

You can configure Firmware Over-The-Air (FOTA) upgrades to replace the applications on both the application core and the network core. The nRF5340 Audio application supports the following types of DFU flash memory layouts:

• Internal flash memory layout - which supports only single-image DFU.
• External flash memory layout - which supports :ref:`multi-image DFU <ug_nrf5340_multi_image_dfu>`.

The LE Audio Controller Subsystem for nRF53 supports both the normal and minimal sizes of the bootloader. The minimal size is specified using the :kconfig:option:`CONFIG_NETBOOT_MIN_PARTITION_SIZE`.

Hardware requirements for external flash memory DFU

To enable the external flash DFU, you need an additional flash memory shield. The nRF5340 Audio application uses the MX25R6435F as the SPI NOR Flash. See the following table for the pin definitions.

DK Pin	SPI NOR Flash pin	Arduino pin
P0.08	SCK	D13
P0.09	MOSI	D11
P0.10	MISO	D12
P1.10	CS	D8

Note

External flash shields must be connected for the kits to boot, even if DFU mode is not initiated.

Enabling FOTA upgrades

The FOTA upgrades are only available when :ref:`nrf53_audio_app_building_script`. With the appropriate parameters provided, the :file:`buildprog.py` Python script will add overlay files for the given DFU type. To enable the desired FOTA functions:

• To define flash memory layout, include the -m internal parameter for the internal layout or the -m external parameter for the external layout.
• To use the minimal size network core bootloader, add the -M parameter.

For the full list of parameters and examples, see the :ref:`nrf53_audio_app_building_script_running` section.

Entering the DFU mode

The |NCS| uses :ref:`SMP server and mcumgr <zephyr:device_mgmt>` as the DFU backend. Unlike the CIS and BIS modes for gateway and headsets, the DFU mode is advertising using the SMP server service. For this reason, to enter the DFU mode, you must long press BTN 4 during each device startup to have the nRF5340 Audio DK enter the DFU mode.

To identify the devices before the DFU takes place, the DFU mode advertising names mention the device type directly. The names follow the pattern in which the device ROLE is inserted before the _DFU suffix. For example:

• Gateway: NRF5340_AUDIO_GW_DFU
• Left Headset: NRF5340_AUDIO_HL_DFU
• Right Headset: NRF5340_AUDIO_HR_DFU

The first part of these names is based on :kconfig:option:`CONFIG_BT_DEVICE_NAME`.

Building and running

This sample can be found under :file:`applications/nrf5340_audio` in the nRF Connect SDK folder structure.

Note

Building and programming the nRF5340 Audio application is different from the :ref:`standard procedure <ug_nrf5340_building>` of building and programming for the nRF5340 DK. This is because the nRF5340 Audio application only builds and programs the files for the application core. |net_core_hex_note|

You can build and program the application in one of the following ways:

• :ref:`nrf53_audio_app_building_script`. This is the suggested method. Using this method allows you to build and program multiple development kits at the same time.
• :ref:`nrf53_audio_app_building_standard`. Using this method requires building and programming each development kit separately.

You might want to check the :ref:`nRF5340 Audio application known issues <known_issues_nrf5340audio>` before building and programming the application.

Testing out of the box

Each development kit comes preprogrammed with basic firmware that indicates if the kit is functional. Before building the application, you can verify if the kit is working by completing the following steps:

1. Plug the device into the USB port.
2. Turn on the development kit using the On/Off switch.
3. Observe RGB1 (bottom side LEDs around the center opening that illuminate the Nordic Semiconductor logo) turn solid yellow, OB/EXT turn solid green, and LED3 start blinking green.

You can now program the development kits with either gateway or headset firmware before they can be used.

Building and programming using script

The suggested method for building the application and programming it to the development kit is running the :file:`buildprog.py` Python script, which is located in the :file:`applications/nrf5340_audio/tools/buildprog` directory. The script automates the process of selecting :ref:`configuration files <nrf53_audio_app_configuration_files>` and building different versions of the application. This eases the process of building and programming images for multiple development kits.

Preparing the JSON file

The script depends on the settings defined in the :file:`nrf5340_audio_dk_devices.json` file. Before using the script, make sure to update this file with the following information for each development kit you want to use:

• nrf5340_audio_dk_snr -- This field lists the SEGGER serial number. You can check this number on the sticker on the nRF5340 Audio development kit. Alternatively, connect the development kit to your PC and run nrfjprog -i in a command window to print the SEGGER serial number of the kit.
• nrf5340_audio_dk_dev -- This field assigns the specific nRF5340 Audio development kit to be a headset or a gateway.
• channel -- This field is valid only for headsets operating in the CIS mode. It sets the channels on which the headset is meant to work. When no channel is set, the headset is programmed as a left channel one.

Running the script

After editing the :file:`nrf5340_audio_dk_devices.json` file, run :file:`buildprog.py` to build the firmware for the development kits. The building command for running the script requires providing the following parameters, in line with :ref:`nrf53_audio_app_configuration_files`:

• Core type (-c parameter): app, net, or both
• Application version (-b parameter): either release or debug
• Device type (-d parameter): headset, gateway, or both
• DFU type (-m parameter): internal, external
• Network core bootloader minimal size (-M)

See the following examples of the parameter usage with the command run from the :file:`buildprog` directory:

• Example 1: The following command builds the application using the script for the application core with the debug application version for both the headset and the gateway:

  python buildprog.py -c app -b debug -d both

• Example 2: The following command builds the application as in example 1, but with the DFU internal flash memory layout enabled and using the minimal size of the network core bootloader:

  python buildprog.py -c app -b debug -d both -m internal -M

  If you run this command with the external DFU type parameter instead of internal, the external flash memory layout will be enabled.

The command can be run from any location, as long as the correct path to :file:`buildprog.py` is given.

The build files are saved in the :file:`applications/nrf5340_audio/build` directory. The script creates a directory for each application version and device type combination. For example, when running the command above, the script creates the :file:`dev_gateway/build_debug` and :file:`dev_headset/build_debug` directories.

Programming with the script

The development kits are programmed according to the serial numbers set in the JSON file. If you run the script with the -p parameter, you can program one or both of the cores after building the files. Make sure to connect the development kits to your PC using USB and turn them on using the POWER switch before you run the command. The command for programming can look as follows:

python buildprog.py -c both -b debug -d both -p

Note

If you are using Windows Subsystem for Linux (WSL) and encounter problems while programming, include the -s parameter to program sequentially.

This command builds the application with the debug application version for both the headset and the gateway and programs the application core. Given the -c both parameter, it also takes the precompiled Bluetooth Low Energy Controller binary from the :file:`applications/nrf5340_audio/bin` directory and programs it to the network core of both the gateway and the headset.

Note

If the programming command fails because of :ref:`readback_protection_error`, run :file:`buildprog.py` with the --recover-on-fail or -f parameter to recover and re-program automatically when programming fails. For example, using the programming command example above:

python buildprog.py -c both -b debug -d both -p --recover-on-fail

Getting help

Run python buildprog.py -h for information about all available script parameters.

Configuration table overview

When running the script command, a table similar to the following one is displayed to provide an overview of the selected options and parameter values:

+------------+----------+---------+--------------+---------------------+---------------------+
| snr        | snr conn | device  | only reboot  | core app programmed | core net programmed |
+------------+----------+---------+--------------+---------------------+---------------------+
| 1010101010 | True     | headset | Not selected | Selected TBD        | Not selected        |
| 2020202020 | True     | gateway | Not selected | Selected TBD        | Not selected        |
| 3030303030 | True     | headset | Not selected | Selected TBD        | Not selected        |
+------------+----------+---------+--------------+---------------------+---------------------+

See the following table for the meaning of each column and the list of possible values:

Column	Indication	Possible values
snr	Serial number of the device, as provided in the :file:`nrf5340_audio_dk_devices.json` file.	Serial number.
snr conn	Whether the device with the provided serial number is connected to the PC with a serial connection.	True - Connected.
		False - Not connected.
device	Device type, as provided in the :file:`nrf5340_audio_dk_devices.json` file.	headset - Headset.
		gateway - Gateway.
only reboot	Whether the device is to be only reset and not programmed. This depends on the -r parameter in the command, which overrides other parameters.	Not selected - No reset.
		Selected TBD - Only reset requested.
		Done - Reset done.
		Failed - Reset failed.
core app programmed	Whether the application core is to be programmed. This depends on the value provided to the -c parameter (see above).	Not selected - Core will not be programmed.
		Selected TBD - Programming requested.
		Done - Programming done.
		Failed - Programming failed.
core net programmed	Whether the network core is to be programmed. This depends on the value provided to the -c parameter (see above).	Not selected - Core will not be programmed.
		Selected TBD - Programming requested.
		Done - Programming done.
		Failed - Programming failed.

Building and programming using command line

You can also build the nRF5340 Audio application using the standard |NCS| :ref:`build steps <gs_programming>` for the command line.

Note

Using this method requires you to build and program each development kit one at a time before moving to the next configuration, which can be time-consuming. :ref:`nrf53_audio_app_building_script` is recommended.

Building the application

Complete the following steps to build the application:

1. Choose the combination of build flags:

   1. Choose the device type by using one of the following options:
      • For headset device: -DCONFIG_AUDIO_DEV=1
      • For gateway device: -DCONFIG_AUDIO_DEV=2
   2. Choose the application version by using one of the following options:
      • For the debug version: No build flag needed.
      • For the release version: -DCONF_FILE=prj_release.conf
   3. (Optional) Choose the DFU flash memory layouts:
      • For internal flash memory DFU: -DCONFIG_AUDIO_DFU=1
      • For external flash memory DFU: -DCONFIG_AUDIO_DFU=2
      • For minimal sizes of the network core bootloader: -DCONFIG_B0N_MINIMAL=y

2. Build the application using the standard :ref:`build steps <gs_programming>`. For example, if you want to build the firmware for the application core as a headset using the release application version, you can run the following command:

   west build -b nrf5340_audio_dk_nrf5340_cpuapp --pristine -- -DCONFIG_AUDIO_DEV=1 -DCONF_FILE=prj_release.conf

   Unlike when :ref:`nrf53_audio_app_building_script`, this command creates the build files directly in the :file:`build` directory. This means that you first need to program the headset development kits before you build and program gateway development kits. Alternatively, you can add the -d parameter to the west command to specify a custom build folder. This lets you build firmware for both headset and gateway before programming any development kits.

Programming the application

After building the files for the development kit you want to program, complete the following steps to program the application from the command line:

1. Plug the device into the USB port.

2. Turn on the development kit using the On/Off switch.

3. Open a command prompt.

4. Run the following command to print the SEGGER serial number of your development kit:

   nrfjprog -i

   Note

   Pay attention to which device is to be programmed with the gateway HEX file and which devices are to be programmed with the headset HEX file.

5. Program the network core on the development kit by running the following command:

   nrfjprog --program bin/*.hex --chiperase --coprocessor CP_NETWORK -r

   |net_core_hex_note|

6. Program the application core on the development kit with the respective HEX file from the :file:`build` directory by running the following command:

   nrfjprog --program build/zephyr/zephyr.hex --coprocessor CP_APPLICATION --sectorerase -r

   In this command, :file:`build/zephyr/zephyr.hex` is the HEX binary file for the application core. If a custom build folder is specified, the path to this folder must be used instead of :file:`build/`.

7. If any device is not programmed due to :ref:`readback_protection_error`, complete the following steps:

   1. Run the following commands to recover the device:

      nrfjprog --recover --coprocessor CP_NETWORK
      nrfjprog --recover

   2. Repeat steps 5 and 6 to program both cores again.

8. When using the default CIS configuration, if you want to use two headset devices, you must also populate the UICR with the desired channel for each headset. Use the following commands, depending on which headset you want to populate:

   • Left headset:

     nrfjprog --memwr 0x00FF80F4 --val 0

   • Right headset:

     nrfjprog --memwr 0x00FF80F4 --val 1

   Select the correct board when prompted with the popup or add the --snr parameter followed by the SEGGER serial number of the correct board at the end of the nrfjprog command.

Testing

After building and programming the application, you can test it for both the CIS and the BIS modes. The following testing scenarios assume you are using USB as the audio source on the gateway. This is the default setting.

Testing the default CIS mode

Complete the following steps to test the CIS mode for one gateway and two headset devices:

1. Make sure that the development kits are still plugged into the USB ports and are turned on. After programming, RGB2 starts blinking green on every device to indicate the ongoing CPU activity on the network core. LED3 starts blinking green on every device to indicate the ongoing CPU activity on the application core.

2. Wait for the LED1 on the gateway to start blinking blue. This happens shortly after programming the development kit and indicates that the gateway device is connected to at least one headset and ready to send data.

3. Search the list of audio devices listed in the sound settings of your operating system for nRF5340 USB Audio (gateway) and select it as the output device.

4. Connect headphones to the HEADPHONE audio jack on both headset devices.

5. Start audio playback on your PC from any source.

6. Wait for LED1 to blink blue on both headsets. When they do, the audio stream has started on both headsets.

   Note

   The audio outputs only to the left channel of the audio jack, even if the given headset is configured as the right headset. This is because of the mono hardware codec chip used on the development kits. If you want to play stereo sound using one development kit, you must connect an external hardware codec chip that supports stereo.

7. Wait for LED2 to light up solid green on the headsets to indicate that the audio synchronization is achieved.

8. Press the VOL+ button on one of the headsets. The playback volume increases for both headsets.

9. Press the VOL- button on the gateway. The playback volume decreases for both headsets.

10. Press the PLAY/PAUSE button on one of the headsets. The playback stops for the given headset and continues on the other one.

11. Press the RESET button on the gateway. The gateway resets and the playback on the unpaused headset stops. After some time, the gateway establishes the connection with both headsets and resumes the playback on the unpaused headset.

12. Press the PLAY/PAUSE button on one of the paused headsets. The playback resumes in sync with the other headset.

13. Press the BTN 4 button on the gateway multiple times. For each button press, the audio stream playback is stopped and the gateway sends a test tone to both headsets. These tones can be used as audio cues to check the synchronization of the headsets.

After the kits have paired for the first time, they are now bonded. This means the Long-Term Key(LTK) is stored on each side, and that the kits will only connect to each other unless the bonding information is cleared. To clear the bonding information, press and hold BTN5 during boot.

When you finish testing, power off the nRF5340 Audio development kits by switching the power switch from On to Off.

Testing the BIS mode

Testing the BIS mode is identical to Testing the default CIS mode, except for the following differences:

• You must :ref:`select the BIS mode manually <nrf53_audio_app_configuration_select_bis>` before building the application.
• You can play the audio stream with different audio settings on the receivers. For example, you can decrease or increase the volume separately for each receiver during playback.

Testing FOTA upgrades

`nRF Connect Device Manager`_ can be used for testing FOTA upgrades. The procedure for upgrading the firmware is identical for both headset and gateway firmware. You can test upgrading the firmware on both cores at the same time on a headset device by completing the following steps:

1. Make sure you have :ref:`configured the application for FOTA <nrf53_audio_app_configuration_configure_fota>`.

2. Install `nRF Connect Device Manager`_ on your Android or iOS device.

3. Connect an external flash shield to the headset.

4. Make sure the headset runs a firmware that supports DFU using external flash memory. One way of doing this is to connect the headset to the USB port, turn it on, and then run this command:

   python buildprog.py -c both -b debug -d headset --pristine -m external -p

   Note

   When using the FOTA related functionality in the :file:`buildprog.py` script on Linux, the python command must execute Python 3.

5. Use the :file:`buildprog.py` script to create a zip file that contains new firmware for both cores:

   python buildprog.py -c both -b debug -d headset --pristine -m external

6. Transfer the generated zip file to your Android or iOS device. The file name should start with :file:`dev_headset_build_debug_dfu_application`. For transfer, you can use cloud services like Google Drive for Android or iCloud for iOS.

7. Open `nRF Connect Device Manager`_ and look for NRF5340_AUDIO_HL_DFU in the scanned devices window. The headset is left by default.

8. Tap on :guilabel:`NRF5340_AUDIO_HL_DFU` and then on the downward arrow icon at the bottom of the screen.

9. In the :guilabel:`Firmware Upgrade` section, tap :guilabel:`SELECT FILE`.

10. Select the zip file you transferred to the device.

11. Tap :guilabel:`START` and then :guilabel:`START` again in the notification to start the DFU process.

12. When the DFU has finished, verify that the new application core and network core firmware works properly.

Adapting application for end products

This section describes the relevant configuration sources and lists the steps required for adapting the nRF5340 Audio application to end products.

Board configuration sources

The nRF5340 Audio application uses the following files as board configuration sources:

• Devicetree Specification (DTS) files - These reflect the hardware configuration. See :ref:`zephyr:dt-guide` for more information about the DTS data structure.
• Kconfig files - These reflect the hardware-related software configuration. See :ref:`kconfig_tips_and_tricks` for information about how to configure them.
• Memory layout configuration files - These define the memory layout of the application.

You can see the :file:`nrf/boards/arm/nrf5340_audio_dk_nrf5340` directory as an example of how these files are structured.

For information about differences between DTS and Kconfig, see :ref:`zephyr:dt_vs_kconfig`. For detailed instructions for adding Zephyr support to a custom board, see Zephyr's :ref:`zephyr:board_porting_guide`.

Application configuration sources

The application configuration source file defines a set of options used by the nRF5340 Audio application. This is a :file:`.conf` file that modifies the default Kconfig values defined in the Kconfig files.

Only one :file:`.conf` file is included at a time. The :file:`prj.conf` file is the default configuration file and it implements the debug application version. For the release application version, you need to include the :file:`prj_release.conf` configuration file. In the release application version no debug features should be enabled.

The nRF5340 Audio application also use several :file:`Kconfig.defaults` files to change configuration defaults automatically, based on the different application versions and device types.

You need to edit :file:`prj.conf` and :file:`prj_release.conf` if you want to add new functionalities to your application, but editing these files when adding a new board is not required.

Adding a new board

Note

The first three steps of the configuration procedure are identical to the steps described in Zephyr's :ref:`zephyr:board_porting_guide`.

To use the nRF5340 Audio application with your custom board:

1. Define the board files for your custom board:
   1. Create a new directory in the :file:`nrf/boards/arm/` directory with the name of the new board.
   2. Copy the nRF5340 Audio board files from the :file:`nrf5340_audio_dk_nrf5340` directory located in the :file:`nrf/boards/arm/` folder to the newly created directory.
2. Edit the DTS files to make sure they match the hardware configuration. Pay attention to the following elements:
   • Pins that are used.
   • Interrupt priority that might be different.
3. Edit the board's Kconfig files to make sure they match the required system configuration. For example, disable the drivers that will not be used by your device.
4. Build the application by selecting the name of the new board (for example, new_audio_board_name) in your build system. For example, when building from the command line, add -b new_audio_board_name to your build command.

FOTA for end products

Do not use the default MCUBoot key for end products. See :ref:`ug_fw_update` and :ref:`west-sign` for more information.

To create your own app that supports DFU, you can use the `nRF Connect Device Manager`_ libraries for Android and iOS.

Dependencies

This application uses the following `nrfx`_ libraries:

• :file:`nrfx_clock.h`
• :file:`nrfx_gpiote.h`
• :file:`nrfx_timer.h`
• :file:`nrfx_dppi.h`
• :file:`nrfx_i2s.h`
• :file:`nrfx_ipc.h`
• :file:`nrfx_nvmc.h`

The application also depends on the following Zephyr libraries:

• :ref:`zephyr:logging_api`

• :ref:`zephyr:kernel_api`

• :ref:`zephyr:api_peripherals`:

  • :ref:`zephyr:usb_api`

• :ref:`zephyr:bluetooth_api`:

  • :file:`include/bluetooth/bluetooth.h`
  • :file:`include/bluetooth/gatt.h`
  • :file:`include/bluetooth/hci.h`
  • :file:`include/bluetooth/uuid.h`

Application configuration options

.. options-from-kconfig::
   :show-type:

Legal notices and disclaimers

Additional Disclaimer for the nRF5340 Audio application

This application and the LE Audio Controller Subsystem for nRF53 are marked as :ref:`experimental <software_maturity>`. The DFU/FOTA functionality in this application is also marked as :ref:`experimental <software_maturity>`.

This LE Audio link controller is tested and works in configurations used by the present reference code (for example, 2 concurrent CIS, or BIS). No other configurations than the ones used in the reference application are tested nor documented in this release.

Important - Battery warnings and mandatory requirements for the nRF5340 Audio DK

The nRF5340 Audio development kit contains a Rechargeable Li-Po battery with 1500 mAh capacity. Please note these warnings and mandatory requirements:

• The battery in this product shall not be replaced by users themselves. Batteries should be removed only by qualified professionals due to safety concerns.
  • Risk of fire or explosion if the battery is replaced by an incorrect type.
  • Disposal of a battery into fire or a hot oven, or mechanically crushing or cutting of a battery can result in an explosion.
  • Leaving a battery in an extremely high temperature surrounding environment can result in an explosion or the leakage of flammable liquid or gas.
  • A battery subjected to extremely low air pressure may result in an explosion or the leakage of flammable liquid or gas.
• The nRF5340 Audio development kit shall not be operated outside the internal battery's charge & discharge temperature range between +10°C and +60°C or stored or transported outside the internal battery's storage temperature.
• Power supply adapter must meet PS1 requirements.

Legal notices for the nRF5340 Audio DK

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Radio frequency notice

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