Device Firmware Upgrade module

Use the DFU module to:

  • Obtain the update image from Configuration channel and store it in the appropriate flash memory partition.

  • Erase the flash memory partition in the background before storing the update image.

Module events

Source Module

Input Event

This Module

Output Event

Sink Module

Source modules for config_event



Bluetooth LE advertising module


Bluetooth LE state module

HID forward module


HID state module

HID Service module

USB state module

Source modules for module_state_event



Sink modules for config_event


Power manager 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 perform the firmware upgrade, you must enable the bootloader. You can use the DFU module with either MCUboot or B0 bootloader. For more information on how to enable the bootloader, see the Bootloader documentation.


If you selected the MCUboot bootloader, the DFU module:

  • Requests the image upgrade after the whole image is transferred over the Configuration channel.

  • Confirms the running image after device reboot.

Enable the DFU module using the CONFIG_DESKTOP_CONFIG_CHANNEL_DFU_ENABLE option. It requires the transport option CONFIG_DESKTOP_CONFIG_CHANNEL_ENABLE to be selected, as it uses Configuration channel for the transmission of the update image.

Set the value of CONFIG_DESKTOP_CONFIG_CHANNEL_DFU_SYNC_BUFFER_SIZE to specify the size of the sync buffer (in words). During the DFU, the data is initially stored in the buffer and then it is moved to flash. The buffer is located in the RAM, so increasing the buffer size increases the RAM usage. If the buffer is small, the host must perform the DFU progress synchronization more often.


The received update image chunks are stored on the dedicated flash memory partition when the current version of the device firmware is running. For this reason, make sure that you use configuration with two image partitions. For more information on configuring the memory layout in the application, see the Flash memory layout documentation.

Implementation details

The DFU module implementation is centered around the transmission and the storage of the update image, and it can be broken down into the following stages:

The firmware transfer operation can also be carried out by Simple Management Protocol module. The application user must not perform more than one firmware upgrade at a time. The modification of the data by multiple application modules would result in a broken image that would be rejected by the bootloader.

Protocol operations

The DFU module depends on the Configuration channel for the correct and secure data transmission between the host and the device. The module provides a simple protocol that allows the update tool on the host to pass the update image to the device.


All the described Configuration channel options are used by the HID configurator for nRF Desktop during the DFU. You can trigger DFU using a single command in the CLI.

The following Configuration channel options are available to perform the firmware update:

  • fwinfo - Passes the information about the currently executed image from the device to the host.

  • reboot - Reboots the device.

  • start - Starts the new update image transmission.

  • data - Passes a chunk of the update image data from the host to the device.

  • sync - Checks the progress of the update image transmission.

  • module_variant - Provides the host with the information about the bootloader variant used on the device.


Perform the fetch operation on this option to get the following information about the currently executed image:

  • Version and length of the image.

  • Partition ID of the image, used to specify the image placement on the flash.


Perform the fetch operation on this option to trigger an instant reboot of the device.


Perform the set operation on this option to start the DFU. The operation contains the following data:

  • Size of the image being transmitted.

  • Checksum of the update image.

  • Offset at which the host tool is going to start the image update. If the image transfer is performed for the first time, the offset must be set to zero.

When the host tool performs the set operation, the checksum and the size are recorded and the update process is started.

If the transmission is interrupted, the current offset position is stored along with the image checksum and size until the device is rebooted. The host tool can restart the update image transfer after the interruption, but the checksum, the requested offset, and the size of the image must match the information stored by the device.


Perform the set operation on this option to pass the chunk of the update image that should be stored at the current offset. The data is initially buffered in RAM, and then it is written to the flash partition after a fetch operation is performed on the sync option.

If the set operation on the data option is successful, the offset in buffer is increased. If the operation fails to be completed, the update process is interrupted.

For performance reasons, the Configuration channel set operation does not return any information back to the host. To check that the update process is correct, the host tool must perform fetch operation on the sync option at regular intervals.


The DFU module does not check if the update image contains any valid data. It also does not check if it is correctly signed. When the update image is received, the host tool requests a reboot. Then, the bootloader will check the image for validity and ensure that the signature is correct. If the verification of the new images is successful, the new version of the application will boot.


Perform the fetch operation on this option to read the following data:

  • Information regarding the status of the update process. The module can report one of the following states:

    • DFU_STATE_CLEANING - The module is erasing the secondary image flash area.

    • DFU_STATE_STORING - The module is writing data to the secondary image flash area.

    • DFU_STATE_ACTIVE - The DFU is ongoing and the module is receiving the new image from the host.

    • DFU_STATE_INACTIVE - The module is not performing any operation, and the DFU can be started.

  • Size of the update image being transmitted.

  • Checksum of the update image.

  • Offset at which the update process currently is.

  • Size of the RAM buffer used to store the data. The host must synchronize the firmware image transfer progress at least on every synchronization buffer byte count.

The update tool can fetch the sync option before starting the update process to see at which offset the update is to be restarted.

Fetching the sync option also triggers moving the image data from the RAM buffer to flash.


Perform the fetch operation on this option to get the information about the bootloader variant that is being used on the device.

Writing data to flash

The image data that is received from the host is initially buffered in the RAM. Writing the data to flash is triggered when the host performs the fetch operation on the sync option. At that point, the HID configurator for nRF Desktop waits until the data is written to flash before providing more image data chunks.

The data is stored in a secondary image flash partition using a dedicated work (k_work_delayable). The work stores a single chunk of data and resubmits itself.

To ensure that the flash write will not interfere with the device usability, the stored data is split into small chunks and written only if there are no HID reports transmitted and the Bluetooth connection state does not change.

Partition preparation

The DFU module must prepare the partition before the update image can be stored. This operation is done in the background.

To ensure that the memory erase will not interfere with the device usability, the memory pages are erased only if there are no HID reports transmitted and the Bluetooth connection state does not change. For example, the memory is not erased right after the Bluetooth connection is established.


The DFU process cannot be started before the entire partition used for storing the update image is erased. If the DFU command is rejected, you must wait until the flash area used for the update image is erased.