Device Firmware Upgrade (DFU) over Bluetooth LE (BLE) is the process that provides ability to update the application, SoftDevice, and bootloader through BLE.

While this example is closely related to the Low Power node example, it is not related to the nRF5 SDK for Mesh DFU functionality described in Configuring and performing DFU over Mesh. The proprietary mesh DFU is not normally suitable for the LPN device, because it requires an always-on radio, which increases power consumption significantly. For this reason, the LPN example uses the DFU solution of the nRF5 SDK, which is GATT-based. In particular, it uses the following features of the nRF5 SDK DFU over BLE functionality:

Buttonless Secure DFU Service that enables entering DFU mode from the application.
Secure Bootloader example to perform the DFU.

The DFU over BLE does not support the side-by-side mode. Once the DFU process starts, the device reboots to the bootloader and the application will not work until the bootloader finishes.

For more information about these features, see nRF5 SDK Bootloader and DFU modules.

Warning: In the Low Power node example, the DFU over BLE support is disabled by default. You need to enable it to continue with this example. To do this, set BLE_DFU_SUPPORT_ENABLED to 1 in examples/lpn/include/nrf_mesh_config_app.h.

Table of contents

Hardware requirements

Performing DFU over BLE using PC requires one additional compatible development kit, besides the development kits required by Low Power node example.

Software requirements

Install the following additional tools:

nRF Util for generating the application signature and the firmware package. See Installing nRF Util for details.
Depending on whether you want to perform DFU using mobile or PC:
- nRF Connect for Mobile (iOS or Android) for performing DFU using a mobile phone.
- nRF Connect for Desktop for performing DFU using a PC.

Setup

The nRF5 SDK project files for the DFU over BLE can be found at: <the path to nRF5 SDK instance>/examples/dfu.

You can find the source code of the Secure Bootloader example at: <path to nRF5 SDK instance>/examples/dfu/secure_bootloader.

The LPN device uses PCA10040 Development Kit. You can find the Secure Bootloader project files for this board in the .../pca10040_s132_ble folder.

Configuring DFU over BLE

The following steps show how to use the Buttonless DFU Service to upgrade the device containing only the bootloader and the SoftDevice (and no user application) with the Low Power example, and then how to further upgrade this example with the new version of its hex file:

Note: If you get the device configuration broken after performing the firmware update, increase the value of the NRF_DFU_APP_DATA_AREA_SIZE parameter. The example code keeps the Bluetooth mesh configuration unchanged when the device enters the DFU mode. So if the device was provisioned before the firmware update, it stays provisioned after the firmware update is completed. This is achieved by configuring the NRF_DFU_APP_DATA_AREA_SIZE parameter that allows to reserve a flash area used by the application. As a consequence, this flash area won't be used by the bootloader when the DFU is performed.

Creating signature for the Low Power node example

To create the keys required for the DFU process:

Create a private key:
nrfutil keys generate lpn_private_key.pem
Create a public key in code format and store it in a file named dfu_public_key.c:
nrfutil keys display --key pk --format code lpn_private_key.pem --out_file dfu_public_key.c
Replace dfu_public_key.c file in the <the path to nRF5 SDK instance>/examples/dfu folder with the new one.

Note: See Working with keys and Signature Verification for more information about signatures.

Generating a firmware package with the Low Power node example

To generate a firmware package:

Make sure the DFU over BLE support is enabled (BLE_DFU_SUPPORT_ENABLED is set to 1 in examples/lpn/include/nrf_mesh_config_app.h).
Build the Low Power node example. To build the example, follow the instructions in Building the Bluetooth mesh stack.
Generate a firmware package with the Low Power node example by using the Low Power node hex file and the private key generated when building the example:
nrfutil pkg generate --application <path-to-lpn-example-hex-file> --application-version <application-version> --hw-version 52 --sd-req 0x0101 --key-file lpn_private_key.pem lpn_dfu_package.zip
In this command:
- Replace <path-to-lpn-example-hex-file> with the path to the LPN example HEX file and the file name.
- Replace <application-version> with any positive number.
  - After the first time upgrade, make sure that each next update has the application version number greater than the current.
- --sd-req can be obtained with the following command:
  nrfutil pkg generate --help

Note: See Generating DFU packages with nRF Util for more information.

Building and programming the bootloader

To perform DFU over BLE update for the Low Power node example, you must build and program the Secure Bootloader example.

Building
To build the bootloader:

Install micro-ecc for nRF5 SDK:
1. Complete steps 2 and 3 from Installing micro-ecc.
2. Compile micro-ecc:
  - On Windows, run build_all.bat.
  - On Ubuntu/Linux and similar systems, run build_all.sh.
Compile the Secure Bootloader example by using one of the following options:
- Compile using SEGGER Embedded Studio (SES): Use the SES project file located under .../ses and follow the Building with SEGGER Embedded Studio instruction.
- Compile using make: Run make under .../armgcc.

Programming
To program the bootloader:

You can use one of the following options:
- Program using SES: Follow the Running examples using SEGGER Embedded Studio instruction.
- Program using make:
```
  $ make erase
  $ make flash_softdevice
  $ make flash
```
Note
See the Programming the bootloader page in the nRF5 SDK documentation for more information.
Observe LED 1 and LED 2 on the device. Both light up when the bootloader enters the DFU mode.

Performing DFU over BLE

The Device Firmware Upgrade over BLE can be performed using either a mobile phone or PC.

Mobile
To perform the DFU transfer over BLE using a mobile phone:

Copy the generated lpn_dfu_package.zip firmware package to your mobile phone.
Use nRF Connect for Mobile to scan for a target device and connect to it:
- If the DFU is performed for the first time, the device will show up as "DfuTarget".
- If the Low Power node example application is already programmed, the device will show up as "nRF5x Mesh LPN Switch".
Press the DFU button to perform DFU.
Provide the zip archive of the application when prompted.

PC
To perform the DFU transfer over BLE using PC:

Plug in the one additional PCA10040 Development Kit.
Add "Bluetooth Low Energy" app to nRF Connect for Desktop.
Select the development kit you plugged in.
Launch "Bluetooth Low Energy" app.
Scan for a target device and connect to it:
- If the DFU is performed for the first time, the device will show up as "DfuTarget".
- If the Low Power node example application is already programmed, the device will show up as "nRF5x Mesh LPN Switch".
Press the DFU button to perform DFU.
Provide the zip archive of the application when prompted.

Regardless of the chosen method, the device resets and runs the new application. It shows up as "nRF5x Mesh LPN Switch" in both the mobile app and on the PC.

To use the DFU over BLE feature for the Low Power example after its configuration, you only need to use the following procedures described above: