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samples: Add split slot A/B sample
Add a variant of the A/B sample that presents how to perform A/B updates in a system, where application and radio images uses separate images and slots. Ref: NCSDK-35733 Signed-off-by: Tomasz Chyrowicz <[email protected]>
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‎samples/dfu/ab_split/CMakeLists.txt‎

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#
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# Copyright (c) 2025 Nordic Semiconductor ASA
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#
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# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
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#
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cmake_minimum_required(VERSION 3.20.0)
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find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
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project(ab_split)
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target_sources(app PRIVATE src/main.c)
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target_sources(app PRIVATE src/ab_utils.c)
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target_include_directories(
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app PRIVATE
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${ZEPHYR_MCUBOOT_MODULE_DIR}/boot/bootutil/include
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${ZEPHYR_MCUBOOT_MODULE_DIR}/boot/zephyr/include
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${ZEPHYR_BASE}/samples/subsys/mgmt/mcumgr/smp_svr/src
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)
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target_sources_ifdef(CONFIG_MCUMGR_TRANSPORT_BT app PRIVATE
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${ZEPHYR_BASE}/samples/subsys/mgmt/mcumgr/smp_svr/src/bluetooth.c)

‎samples/dfu/ab_split/Kconfig‎

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#
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# Copyright (c) 2025 Nordic Semiconductor ASA
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#
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# SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
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#
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config N_BLINKS
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int "Number of fast blinks"
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default 1
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config EMULATE_APP_HEALTH_CHECK_FAILURE
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bool "Blocks confirmation of being healthy after the update"
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source "Kconfig.zephyr"

‎samples/dfu/ab_split/README.rst‎

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.. _ab_split_sample:
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A/B with MCUboot and separated slots
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####################################
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.. contents::
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:local:
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:depth: 2
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The A/B with MCUboot and separated slots sample demonstrates how to configure the application for updates using the A/B method using MCUboot.
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This sample is a variant of the :ref:`A/B sample <ab_sample>`, where the application and radio images are not merged, but reside in separate MCUboot slots.
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This split increases demand on the number of memory areas that should be individually locked from accidental writes as well as requires additional care when preparing updates, so only a compatible set of slots are booted.
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The additional dependency check during the boot process increases the time to boot the system.
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It also includes an example to perform a device health check before confirming the image after the update.
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You can update the sample using the Simple Management Protocol (SMP) with UART or Bluetooth® Low Energy.
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To prevent the build system from merging slots, the sysbuild :kconfig:option:`SB_CONFIG_MCUBOOT_SIGN_MERGED_BINARY` option is disabled.
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To enable manifest-based dependency management, the :kconfig:option:`SB_CONFIG_MCUBOOT_MANIFEST_UPDATES=y` option is enabled in the :file:`sysbuild/mcuboot/prj.conf` file.
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Requirements
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************
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The sample supports the following development kits:
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.. table-from-sample-yaml::
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You need the nRF Device Manager app for update over Bluetooth Low Energy:
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* `nRF Device Manager mobile app for Android`_
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* `nRF Device Manager mobile app for iOS`_
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Overview
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********
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This sample demonstrates firmware update using the A/B method.
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This method allows two copies of the application in the NVM memory.
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It is possible to switch between these copies without performing a swap, which significantly reduces time of device's unavailability during the update.
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The switch between images can be triggered by the application or, for example, by a hardware button.
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This sample implements an SMP server.
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SMP is a basic transfer encoding used with the MCUmgr management protocol.
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For more information about MCUmgr and SMP, see :ref:`device_mgmt`.
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The sample supports the following MCUmgr transports by default:
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* Bluetooth
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* Serial (UART)
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A/B functionality
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=================
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When the A/B with separated slots functionality is used, the device has two slots for each application and radio firmwares: slot A and slot B.
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The slots are equivalent, and the device can boot from either of them.
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By design, the slot A of the application image boots the slot A of the radio image, so there is a manifest-based dependency required to correctly verify the correctness of the image pairs.
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In the case of MCUboot, this is achieved by using the Direct XIP feature.
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Thus, note that the terms slot 0, primary slot, slot A and slot 1, secondary slot, slot B are used interchangeably throughout the documentation.
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This configuration allows a background update of the non-active slot while the application runs from the active slot.
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After the update is complete, the device can quickly switch to the updated slot on the next reboot.
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The following conditions decide which slot will be booted (active) on the next reboot:
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1. If one of the slots contains a valid image, it is marked as valid only if the same slot of the other image is also valid.
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#. If one of the slots is not valid, the other slot is selected as active.
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#. If both slots are valid, the slot marked as "preferred" is selected as active.
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#. If both slots are valid and none is marked as "preferred," the slot with the higher version number is selected as active.
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#. If none of the above conditions is met, slot A is selected as active.
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You can set the preferred slot using the ``boot_request_set_preferred_slot`` function.
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Currently, this only sets the boot preference for a single reboot.
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Identifying the active slot
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---------------------------
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If the project uses the Partition Manager, the currently running slot can be identified by checking if ``CONFIG_NCS_IS_VARIANT_IMAGE`` is defined.
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If it is defined, the application is running from slot B.
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Otherwise, it is running from slot A.
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If the project does not use the Partition Manager (a configuration currently only supported on the nRF54H20), the currently running slot can be identified by comparing the address pointed `zephyr,code-partition` to specific node addresses defined in the device tree.
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The following node partitions are used by default:
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* ``cpuapp_slot0_partition`` - Application core, slot A
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* ``cpuapp_slot1_partition`` - Application core, slot B
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* ``cpurad_slot0_partition`` - Radio core, slot A
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* ``cpurad_slot1_partition`` - Radio core, slot B
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For example, verifying that the application is running from slot A can be done by using the following macro:
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.. code-block:: c
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#define IS_RUNNING_FROM_SLOT_A \
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(FIXED_PARTITION_NODE_OFFSET(DT_CHOSEN(zephyr_code_partition)) == \
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FIXED_PARTITION_OFFSET(cpuapp_slot0_partition))
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.. _ab_split_build_files:
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Build files
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-----------
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This sample overrides the default build strategy, so application and radio images are built separately.
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In this case, the following files should be sent to the device when performing an update:
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* :file:`build/mcuboot_secondary_app/zephyr/zephyr.signed.bin` - Contains the slot B of the application image.
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This file should be uploaded to the secondary slot when the device is running from slot A.
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* :file:`build/ipc_radio_secondary_app/zephyr/zephyr.signed.bin` - Contains the slot B of the radio image.
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This file should be uploaded to the secondary slot when the device is running from slot A.
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* :file:`build/ab/zephyr/zephyr.signed.bin` - Contains the slot A of the application image.
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This file should be uploaded to the primary slot when the device is running from slot B.
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* :file:`build/ipc_radio/zephyr/zephyr.signed.bin` - Contains the slot A of the radio image.
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This file should be uploaded to the primary slot when the device is running from slot B.
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User interface
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**************
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LED 0:
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This LED indicates that the application is running from slot A.
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It is controlled as active low, meaning it will turn on once the application is booted and blinks (turns off) in short intervals.
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The number of short blinks is configurable using the :kconfig:option:`CONFIG_N_BLINKS` Kconfig option.
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It will remain off if the application is running from slot B.
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LED 1:
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This LED indicates that the application is running from slot B.
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It is controlled as active low, meaning it will turn on once the application is booted and blinks (turns off) in short intervals.
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The number of short blinks is configurable using the :kconfig:option:`CONFIG_N_BLINKS` Kconfig option.
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It will remain off if the application is running from slot A.
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Button 0:
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By pressing this button, the non-active slot will be selected as the preferred slot on the next reboot.
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This preference applies only to the next boot and is cleared after the subsequent reset.
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Configuration
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*************
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|config|
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Configuration options
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=====================
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Check and configure the following configuration option for the sample:
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.. _CONFIG_N_BLINKS:
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CONFIG_N_BLINKS - The number of blinks.
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This configuration option sets the number of times the LED corresponding to the currently active slot blinks (LED0 for slot A, LED1 for slot B).
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The default value of the option is set to ``1``, causing a single blink to indicate *Version 1*.
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You can increment this value to represent an update, such as set it to ``2`` to indicate *Version 2*.
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.. _CONFIG_EMULATE_APP_HEALTH_CHECK_FAILURE:
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CONFIG_EMULATE_APP_HEALTH_CHECK_FAILURE - Enables emulation of a broken application that fails the self-test.
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This configuration option emulates a broken application that does not pass the self-test.
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Additional configuration
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========================
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Check and configure the :kconfig:option:`CONFIG_MCUBOOT_IMGTOOL_SIGN_VERSION` library Kconfig option specific to the MCUboot library.
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This configuration option sets the version to pass to imgtool when signing.
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To ensure the updated build is preferred after a DFU, set this option to a higher version than the version currently running on the device.
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Building and running
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********************
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.. |sample path| replace:: :file:`samples/dfu/ab`
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.. include:: /includes/build_and_run.txt
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Testing
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=======
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To perform DFU using the `nRF Connect Device Manager`_ mobile app, complete the following steps:
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.. include:: /app_dev/device_guides/nrf52/fota_update.rst
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:start-after: fota_upgrades_over_ble_nrfcdm_common_dfu_steps_start
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:end-before: fota_upgrades_over_ble_nrfcdm_common_dfu_steps_end
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Instead of using the :file:`dfu_application.zip` file, you can also send the appropriate binary file directly, as described in :ref:`ab_build_files`.
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Make sure to select the correct file based on the currently running slot.
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Dependencies
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************
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This sample uses the following |NCS| library:
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* :ref:`MCUboot <mcuboot_index_ncs>`

‎samples/dfu/ab_split/boards/nrf54h20dk_nrf54h20_cpuapp.overlay‎

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/*
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* Copyright (c) 2025 Nordic Semiconductor ASA
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*
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* SPDX-License-Identifier: LicenseRef-Nordic-5-Clause
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*/
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#include "../sysbuild/nrf54h20dk_nrf54h20_memory_map.dtsi"
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/ {
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chosen {
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zephyr,boot-mode = &boot_request;
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};
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};

‎samples/dfu/ab_split/prj.conf‎

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# Enable MCUmgr and dependencies.
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CONFIG_NET_BUF=y
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CONFIG_ZCBOR=y
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CONFIG_CRC=y
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CONFIG_MCUMGR=y
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CONFIG_STREAM_FLASH=y
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CONFIG_FLASH_MAP=y
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# Some command handlers require a large stack.
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CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2304
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CONFIG_MAIN_STACK_SIZE=2176
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# Ensure an MCUboot-compatible binary is generated.
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CONFIG_BOOTLOADER_MCUBOOT=y
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# Enable flash operations.
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CONFIG_FLASH=y
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# Required by the `taskstat` command.
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CONFIG_THREAD_MONITOR=y
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# Support for taskstat command
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CONFIG_MCUMGR_GRP_OS_TASKSTAT=y
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# Enable statistics and statistic names.
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CONFIG_STATS=y
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CONFIG_STATS_NAMES=y
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# Enable most core commands.
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CONFIG_FLASH=y
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CONFIG_IMG_MANAGER=y
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CONFIG_MCUMGR_GRP_IMG=y
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CONFIG_MCUMGR_GRP_OS=y
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CONFIG_MCUMGR_GRP_STAT=y
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# Enable logging
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CONFIG_LOG=y
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CONFIG_MCUBOOT_UTIL_LOG_LEVEL_WRN=y
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# Disable debug logging
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CONFIG_LOG_MAX_LEVEL=3
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# Enable boot requests through retained memory.
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CONFIG_RETAINED_MEM=y
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CONFIG_RETENTION=y
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CONFIG_NRF_MCUBOOT_BOOT_REQUEST=y
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CONFIG_RETENTION_BOOT_MODE=y
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CONFIG_MCUMGR_GRP_OS_RESET_BOOT_MODE=y
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# Enable DK LED/button library
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CONFIG_DK_LIBRARY=y
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# Configure bluetooth
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CONFIG_BT=y
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CONFIG_BT_PERIPHERAL=y
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# Allow for large Bluetooth data packets.
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CONFIG_BT_L2CAP_TX_MTU=498
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CONFIG_BT_BUF_ACL_RX_SIZE=502
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CONFIG_BT_BUF_ACL_TX_SIZE=502
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CONFIG_BT_CTLR_DATA_LENGTH_MAX=251
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# Enable the Bluetooth mcumgr transport (unauthenticated).
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CONFIG_MCUMGR_TRANSPORT_BT=y
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CONFIG_MCUMGR_TRANSPORT_BT_CONN_PARAM_CONTROL=y
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# Enable the Shell mcumgr transport.
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CONFIG_BASE64=y
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CONFIG_CRC=y
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CONFIG_SHELL=y
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CONFIG_SHELL_BACKEND_SERIAL=y
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CONFIG_MCUMGR_TRANSPORT_SHELL=y
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# Enable the mcumgr Packet Reassembly feature over Bluetooth and its configuration dependencies.
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# MCUmgr buffer size is optimized to fit one SMP packet divided into five Bluetooth Write Commands,
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# transmitted with the maximum possible MTU value: 498 bytes.
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CONFIG_MCUMGR_TRANSPORT_BT_REASSEMBLY=y
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CONFIG_MCUMGR_TRANSPORT_NETBUF_SIZE=2475
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CONFIG_MCUMGR_GRP_OS_MCUMGR_PARAMS=y
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CONFIG_MCUMGR_TRANSPORT_WORKQUEUE_STACK_SIZE=4608
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# Enable the LittleFS file system.
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CONFIG_FILE_SYSTEM=y
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CONFIG_FILE_SYSTEM_LITTLEFS=y
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# Enable file system commands
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CONFIG_MCUMGR_GRP_FS=y
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# Enable the storage erase command.
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CONFIG_MCUMGR_GRP_ZBASIC=y
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CONFIG_MCUMGR_GRP_ZBASIC_STORAGE_ERASE=y
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# Disable Bluetooth ping support
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CONFIG_BT_CTLR_LE_PING=n
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# Disable shell commands that are not needed
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CONFIG_CLOCK_CONTROL_NRF_SHELL=n
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CONFIG_DEVICE_SHELL=n
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CONFIG_DEVMEM_SHELL=n
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CONFIG_FLASH_SHELL=n

‎samples/dfu/ab_split/sample.yaml‎

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sample:
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description: AB update sample with separated slots
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name: ab_split
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common:
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sysbuild: true
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build_only: true
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tags:
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- dfu_ab
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- ci_samples_dfu
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tests:
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sample.dfu.ab_split:
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sysbuild: true
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platform_allow:
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- nrf54h20dk/nrf54h20/cpuapp
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integration_platforms:
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- nrf54h20dk/nrf54h20/cpuapp

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