nRF Connect SDK v1.9.1 Release Notes

nRF Connect SDK delivers reference software and supporting libraries for developing low-power wireless applications with Nordic Semiconductor products in the nRF52, nRF53, and nRF91 Series. The SDK includes open source projects (TF-M, MCUboot, OpenThread, Matter, and the Zephyr RTOS), which are continuously integrated and re-distributed with the SDK.

Release notes might refer to “experimental” support for features, which indicates that the feature is incomplete in functionality or verification, and can be expected to change in future releases. The feature is made available in its current state though the design and interfaces can change between release tags. The feature will also be labelled with “EXPERIMENTAL” in Kconfig files to indicate this status. Build warnings will be generated to indicate when features labelled EXPERIMENTAL are included in builds unless the Kconfig option CONFIG_WARN_EXPERIMENTAL is disabled.


  • Fixed bugs related to Bluetooth® LE conformance, Thread, TF-M, and to nRF Machine Learning application for Thingy:53. See Changelog for details.

Release tag

The release tag for the nRF Connect SDK manifest repository ( is v1.9.1. Check the west.yml file for the corresponding tags in the project repositories.

To use this release, check out the tag in the manifest repository and run west update. See Get the nRF Connect SDK code for more information.

For information on the included repositories and revisions, see Repositories and revisions for v1.9.1.

IDE support

nRF Connect SDK v1.9.1 is supported by both nRF Connect for Visual Studio Code and SEGGER Embedded Studio Nordic Edition. In future releases, documentation on the setup and usage of Segger Embedded Studio Nordic Edition will no longer be available and all references to IDE support will instruct users with nRF Connect for Visual Studio Code. In future releases, Segger Embedded Studio will no longer be tested with the build system and it is not recommended for new projects.

nRF Connect extensions for Visual Studio Code will be under continued active development and supported and tested with future nRF Connect SDK releases. It is recommended for all new projects.

Supported modem firmware

See Modem firmware compatibility matrix for an overview of which modem firmware versions have been tested with this version of the nRF Connect SDK.

Use the latest version of the nRF Programmer app of nRF Connect for Desktop to update the modem firmware. See Updating the modem firmware for instructions.

Known issues

Known issues are only tracked for the latest official release. See known issues for nRF Connect SDK v1.9.1 for the list of issues valid for the latest release.


The following sections provide detailed lists of changes by component.


This section provides detailed lists of changes by protocol.

Bluetooth LE

  • Fixed an issue with the response error code for L2CAP request on a channel that has encryption requirement.


  • Updated OpenThread libraries with a set of bug fixes from Zephyr upstream. See the Zephyr section for details.


nRF Machine Learning

  • Fixed the NCSDK-13923 known issue that would cause the nRF52840 DK to crash when an Android device was connected over Bluetooth LE.

RF Front-End Modules

  • Updated the default radiated output power to 10dBm for nRF21540.

Trusted Firmware-M

  • Fixed:

    • NCSDK-14015 known issue that would cause crash during boot when the CONFIG_RPMSG_SERVICE Kconfig option was enabled on the nRF5340 SoC.

    • NCSDK-13949 known issue where the TF-M Secure Image would copy FICR to RAM on nRF9160.


The Zephyr fork in nRF Connect SDK (sdk-zephyr) contains all commits from the upstream Zephyr repository up to and including 45ef0d2, plus some nRF Connect SDK specific additions. This is the same commit ID as the one used for nRF Connect SDK v1.9.0.

For a complete list of nRF Connect SDK specific commits since v1.9.0, run the following command:

git log --oneline manifest-rev ^v2.7.99-ncs1

Zephyr changes incorporated into nRF Connect SDK

This section contains changes in Zephyr that were cherry-picked into nRF Connect SDK for this release.

  • Fixed:

    • KRKNWK-13059 known issue where a Thread 1.2 device would occasionally send the wrong Link Layer Frame Counter TLV, which would make the link with the neighbor unusable.

    • An issue where a Thread 1.2 device would occasionally assert due to wrong transmission error being reported to the MAC layer.

    • An issue where a Thread device would not properly handle fragmented IPv6 packets.

    • An issue where sensor readouts on Thingy:53 would be unstable due to PMIC not being set to the PWM mode.

    • An issue where SPI communication with sensors on Thingy:53 would be hindered because of the SPI interface being controlled by nRF5340 network core, instead of the application core.