How do I use a custom version of Zephyr with NCS?

RE: How do I use a custom version of Zephyr with NCS?

Einar Thorsrud — Wed, 10 Sep 2025 07:22:03 GMT

I believe using your own fork of Zephyr is OK as long as it is based on the exact version/hash that was used in the SDK that is qualified, and you do not make any changes related to the Bluetooth stack. If so, using your approach should be OK when you just modify the custom drivers.

RE: How do I use a custom version of Zephyr with NCS?

Atilla Byteflyer — Tue, 09 Sep 2025 08:04:10 GMT

Actually I'm using an internal branch based on ncs-v3.1.0 release, because some of the peripheral drivers in Zephyr are lacking. Wither no power management, or happen to lack "compatible" support for the variants we use etc.

Instead of maintaining custom drivers in our external tree, I thought it would be more manageable to fork NCS version of Zephyr, which would also make it easy to contribute back upstream.

Do you have a recommendation in the regulatory sense? Should we keep any custom driver developments (even things like temperature sensors) strictly out-of-tree?

RE: How do I use a custom version of Zephyr with NCS?

PaKa — Tue, 09 Sep 2025 01:56:00 GMT

Out of curisosity, why do you want to do this? All wireless certifications are tied to the Zephyr version version included in nRF Connect SDK so you will now not have any Bluetooth/Matter/Thread qualifications for products.

RE: How do I use a custom version of Zephyr with NCS?

Atilla Byteflyer — Wed, 03 Sep 2025 11:56:40 GMT

Thank you for the pointer. I provided my solution for future reference.

RE: How do I use a custom version of Zephyr with NCS?

Atilla Byteflyer — Wed, 03 Sep 2025 11:56:02 GMT

Solved it this way: Explicitly adding the Zephyr before NCS will override the Zephyr from NCS.

manifest:
 self:
 west-commands: scripts/west-commands.yml

remotes:
 - name: <own remote>
   url-base: https://github.com/<own>
 - name: ncs
   url-base: https://github.com/nrfconnect

projects:
 - name: zephyr
   remote: <own remote>
   repo-path: zephyr
   # always point this to a tag(better) or hash, never a branch!
   revision: <own tag>
   import:
   # Recursively import these from Zephyr
   # Please keep this list sorted alphabetically.
     name-allowlist:
     - ...

- name: nrf
  repo-path: sdk-nrf
  remote: ncs
  revision: v3.1.0
  # recursively import EVERYTHING from NCS.
  # This has lower priority than explicitly listed ones.
  # Zephyr above overrides the zephyr from NCS
  import: true

RE: How do I use a custom version of Zephyr with NCS?

Einar Thorsrud — Fri, 29 Aug 2025 12:00:21 GMT

Hi,

The way I understand your question you want to refer to use a nRF Connect SDK release, but refer to another Zephyr tag? One potential approach could be to do as is domein the nRF Connect SDK example application (which demonstrate a workspace application) but instead of referring to nrf, refer to all the compoennts you want (including Zephyr and others), so that you maitain your own west.yml that is based on the one under nrf: west.yml. It may be just as clean to fork nrf repo and do things there though, although I understand that is somehting you want to avoid.