Device Firmware Upgrade MCUmgr module

The Device Firmware Upgrade MCUmgr module is responsible for performing a Device Firmware Upgrade (DFU) over Simple Management Protocol (SMP).

If you enable the Bluetooth LE as transport, you can perform the DFU using, for example, the nRF Connect for Mobile application. The DFU button appears in the tab of the connected Bluetooth device that supports the image transfer over the Simple Management Protocol (SMP). After pressing the button, you can select the *.bin file used for the firmware update. See the Image transfer over SMP section for information about which binary file should be used for the DFU image transfer.


The Device Firmware Upgrade MCUmgr module implementation is currently marked as experimental because it uses internal MCUmgr API.

Module events

Source Module

Input Event

This Module

Output Event

Sink Module

Source modules for module_state_event



Device Firmware Upgrade MCUmgr module


Simple Management Protocol module


Bluetooth LE latency module

Device Firmware Upgrade MCUmgr module

Simple Management Protocol module


See the Overview: Firmware architecture for more information about the event-based communication in the nRF Desktop application and about how to read this table.


To enable the module, set the CONFIG_DESKTOP_DFU_MCUMGR_ENABLE Kconfig option.

The module selects the following configurations:

To use the module, you must also enable the CONFIG_BOOTLOADER_MCUBOOT Kconfig option. The DFU over Simple Management Protocol in Zephyr is supported only with the MCUboot bootloader.

By default, the MCUmgr DFU module confirms the image using the boot_write_img_confirmed() function during the system boot. If the CONFIG_DESKTOP_DFU_MCUMGR_MCUBOOT_DIRECT_XIP option is enabled, the MCUmgr DFU module assumes that the bootloader simply boots the image with a higher version and does not confirm the newly updated image after a successful boot. Make sure that CONFIG_DESKTOP_DFU_MCUMGR_MCUBOOT_DIRECT_XIP Kconfig option is enabled if devices use the MCUboot bootloader in direct-xip mode. The option is enabled by default if CONFIG_BOOT_BUILD_DIRECT_XIP_VARIANT is enabled.

You must also enable the preferred transport for the MCUmgr’s SMP protocol (for example, the CONFIG_MCUMGR_TRANSPORT_BT Kconfig option). With the CONFIG_MCUMGR_TRANSPORT_BT Kconfig option enabled, the module enables the CONFIG_CAF_BLE_SMP_TRANSFER_EVENTS event. The event can be used to lower Bluetooth connection latency during the DFU process.

The DFU module leverages the DFU lock utility to synchronize flash access with other DFU methods (for example, the Device Firmware Upgrade module). Set the CONFIG_DESKTOP_DFU_LOCK Kconfig option to enable this feature. Make sure that the DFU lock utility is enabled if your nRF Desktop application configuration uses multiple DFU transports.

You cannot use this module with the CAF: Simple Management Protocol module. In other words, you cannot simultaneously enable the CONFIG_DESKTOP_DFU_MCUMGR_ENABLE option and the CONFIG_CAF_BLE_SMP Kconfig option.

Implementation details

The module uses MCUmgr’s image notification callbacks for the following purposes:

  • To periodically submit a ble_smp_transfer_event while image upload over Bluetooth LE is in progress. The module registers itself as the final subscriber of the event to track the number of submitted events. If a ble_smp_transfer_event was already submitted, but was not yet processed, the module desists from submitting subsequent events.

  • To reject image upload or system reboot request if DFU lock utility is already taken by another DFU transport.

The DFU MCUmgr implementation uses the DFU lock utility. On each DFU attempt, the module attempts to claim ownership over the DFU flash using the DFU lock utility API. It holds the DFU owner status until the DFU process is completed or timed out. The module assumes that DFU is timed out if the registered MCUmgr notification hooks are not called for 5 seconds. If the module is not the current DFU owner, it rejects the DFU commands that either write to the DFU flash or reboot the device. The module also resets the MCUmgr DFU progress once the lock is claimed by a different owner.