nrfutil is a Python package that includes the nrfutil command line utility and the nordicsemi library.

The library is written for Python 2.7.

There are 2 different and incompatible DFU package formats:

• legacy: used a simple structure and no security
• modern: uses Google's protocol buffers for serialization and can be cryptographically signed

The DFU package format transitioned from legacy to modern in SDK 11.1. Depending on the SDK version that you are using you will need to select a release of this tool compatible with it:

• Version 0.5.0 generates legacy firmware packages compatible with nRF SDK 11.0 and older
• Version 1.0.0 and later generate modern firmware packages compatible with nRF SDK 11.1 and newer

To install nrfutil the following prerequisites must be satisfied:

• Python 2.7 (2.7.6 or newer, not Python 3)
• pip (https://pip.pypa.io/en/stable/installing.html)
• setuptools (upgrade to latest version: pip install -U setuptools)
• install required modules: pip install -r requirements.txt

py2exe prerequisites (Windows only):

• py2exe (Windows only) (v0.6.9) (pip install http://sourceforge.net/projects/py2exe/files/latest/download?source=files)
• VC compiler for Python (Windows only) (http://www.microsoft.com/en-us/download/confirmation.aspx?id=44266)

To install the library to the local Python site-packages and script folder:

python setup.py install

To generate a self-contained Windows exe version of the utility (Windows only):

python setup.py py2exe

NOTE: Some anti-virus programs will stop py2exe from executing correctly when it modifies the .exe file.

To get info on usage of nrfutil:

nrfutil --help

There are several commands that you can use to perform different tasks related to DFU:

This set of commands allow you to both generate a package for over-the-air DFU or perform an actual update over a serial line.

Generate a package (.zip file) that you can later use with a mobile application or any other means to update the firmware of an nRF5x IC over the air. This command takes several options that you can list using:

nrfutil dfu genpkg --help

Below is an example of the generation of a package from an application's app.hex file:

nrfutil dfu genpkg --application app.hex --key-file key.pem app_dfu_package.zip

Perform a full DFU procedure over a serial (UART) line. This command takes several options that you can list using:

nrfutil dfu serial --help

Below is an example of the execution of a DFU procedure of the file generated above over COM3 at 115200 bits per second:

nrfutil dfu serial -pkg app_dfu_package.zip -p COM3 -b 115200

This set of commands allow you to generate and display cryptographic keys used to sign and verify DFU packages.

Generate a private (signing) key and store it in a file in PEM format. The following will generate a private key and store it in a file named private.pem:

nrfutil keys generate private.pem

Display a private (signing) or public (verification) key from a PEM file taken as input. This command takes several options that you can list using:

nrfutil keys display --help

Below is an example of displaying a public key in code format from the key file generated above:

nrfutil keys display --key pk --format code private.pem

This command displays the version of nrfutil.