.. _dfu:

Device Firmware Upgrade
#######################

Overview
********

The Device Firmware Upgrade subsystem provides the necessary frameworks to
upgrade the image of a Zephyr-based application at run time. It currently
consists of two different modules:

* :zephyr_file:`subsys/dfu/boot/`: Interface code to bootloaders
* :zephyr_file:`subsys/dfu/img_util/`: Image management code

The DFU subsystem deals with image management, but not with the transport
or management protocols themselves required to send the image to the target
device. For information on these protocols and frameworks please refer to the
:ref:`device_mgmt` section.

Bootloaders
***********

.. _mcuboot:

MCUboot
=======

Zephyr is directly compatible with the open source, cross-RTOS
`MCUboot boot loader`_. It interfaces with MCUboot and is aware of the image
format required by it, so that Device Firmware Upgrade is available when MCUboot
is the boot loader used with Zephyr. The source code itself is hosted in the
`MCUboot GitHub Project`_ page.

In order to use MCUboot with Zephyr you need to take the following into account:

1. You will need to define the flash partitions required by MCUboot; see
   :ref:`flash_map_api` for details.
2. You will have to specify your flash parition as the chosen code partition

.. code-block:: devicetree

   / {
      chosen {
         zephyr,code-partition = &slot0_partition;
      };
   };

3. Your application's :file:`.conf` file needs to enable the
   :kconfig:`CONFIG_BOOTLOADER_MCUBOOT` Kconfig option in order for Zephyr to
   be built in an MCUboot-compatible manner
4. You need to build and flash MCUboot itself on your device
5. You might need to take precautions to avoid mass erasing the flash and also
   to flash the Zephyr application image at the correct offset (right after the
   bootloader)

More detailed information regarding the use of MCUboot with Zephyr  can be found
in the `MCUboot with Zephyr`_ documentation page on the MCUboot website.

.. _MCUboot boot loader: https://mcuboot.com/
.. _MCUboot with Zephyr: https://mcuboot.com/documentation/readme-zephyr/
.. _MCUboot GitHub Project: https://github.com/runtimeco/mcuboot