Cellular: HTTP modem delta update

The HTTP modem delta update sample demonstrates how to do a delta update of the modem firmware. A delta update is an update that contains only the code that has changed, not the entire firmware.

The sample uses the FOTA download library to download a file from a remote server and write it to the modem.


The sample supports the following development kits:

Hardware platforms


Board name

Build target

nRF9161 DK



nRF9160 DK




When built for an _ns build target, the sample is configured to compile and run as a non-secure application with Cortex-M Security Extensions enabled. Therefore, it automatically includes Trusted Firmware-M that prepares the required peripherals and secure services to be available for the application.


The sample connects to an HTTP server to download a signed modem delta image. The delta images are part of the official modem firmware releases. The sample automatically downloads the correct delta image to go from the base version to the test version, or the test version to the base version, depending on the currently installed version.

Sending traces over UART on an nRF91 Series DK

To send modem traces over UART on an nRF91 Series DK, configuration must be added for the UART device in the devicetree and Kconfig. This is done by adding the modem trace UART snippet when building and programming.

Use the Cellular Monitor app for capturing and analyzing modem traces.

Building and running

This sample can be found under samples/cellular/http_update/modem_delta_update in the nRF Connect SDK folder structure.

When built as firmware image for the _ns build target, the sample has Cortex-M Security Extensions (CMSE) enabled and separates the firmware between Non-Secure Processing Environment (NSPE) and Secure Processing Environment (SPE). Because of this, it automatically includes the Trusted Firmware-M (TF-M). To read more about CMSE, see Processing environments.

To build the sample with Visual Studio Code, follow the steps listed on the How to build an application page in the nRF Connect for VS Code extension documentation. See Building and programming an application for other building and programming scenarios and Testing and debugging an application for general information about testing and debugging in the nRF Connect SDK.


After programming the sample to your development kit,, test it by performing the following steps:

  1. Note the LED pattern (1 or 2 LEDs).

  2. Press Button 1 on the nRF91 Series DK or type “download” in the terminal emulator to start downloading the delta modem firmware update. Wait for the download to complete.

  3. Press Button 1 on the nRF91 Series DK or type “apply” in the terminal emulator to apply the delta modem firmware update. Once the modem update procedure is complete, the modem is reinitialized to run the new firmware.

  4. Observe that the LED pattern has changed (1 vs 2).

  5. Start over from point 1, to perform the delta update back to the previous version.


This sample uses the following nRF Connect SDK libraries:

It uses the following sdk-nrfxlib library:

It uses the following Zephyr libraries:

In addition, it uses the following secure firmware component: