Modify zephyr's Driver with out of tree procedure

RE: Modify zephyr's Driver with out of tree procedure

helpfulchicken — Sat, 07 Jun 2025 23:34:33 GMT

I had a similar issue (difficulties making a custom modem driver work), and I finally got it working so I thought I would share my key findings here to help the next poor soul to stumble here while working on a similar problem.

As mentioned above, when building your code with your custom driver amendment, you need to have list(APPEND ZEPHYR_EXTRA_MODULES path_to/my_module but a key detail that is easy to miss is that it needs to be BEFORE the step where you call find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE}). This is probably the main thing that tripped me up for a long time.

# - this 'append extra modules' step must be prior to the 'find package zephyr' step!
list(APPEND ZEPHYR_EXTRA_MODULES ${MAIN_REPO_DIRECTORY}/custom_driver_module)

find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})

project(app)

Use zephyr_library_amend() as mentioned above, to specify how the driver is to be built as an addition to an existing driver library. Don't include duplicates of the existing source files from the driver library you're trying to add to or you'll you'll get 'multiple definitions' conflicts, keep it to just your new functions etc. Duplicate + modified Kconfig files don't seem to be an issue. Based on this, having files like modem_context.c in your custom driver will cause conflicts, unless your copy only adds new function names.

The general folder structure shown in the original post should work. You need the dts/bindings/my_module/company,thing.yml file so that you can specify your thing in the devicetree files in the 'compatible' property. I didn't find that I needed the include/app/drivers/ portion, I just put my quectel-bg95cd.h equivalent into the drivers/modem folder.

This was my folder structure which worked for me:

boards
└── ...

custom_driver_module
├── drivers
|   ├── modem
|   |   ├── CMakeLists
|   |   ├── Kconfig
|   |   ├── Kconfig.quectel-bg95cd
|   |   ├── quectel_bg95cd.c
|   |   └── quectel_bg95cd.h
|   ├── CMakeLists.txt
|   └── Kconfig
├── dts
|   └── bindings
|       └── modem
|           └── quectel,bg95cd.yaml
├── zephyr
|   └── module.yml
├── CMakeLists.txt
└── Kconfig

app
├── boards
|   └── ...
├── src
|   └── ...
└── CMakeLists.txt

I hope this helps someone.

RE: Modify zephyr's Driver with out of tree procedure

Hieu — Mon, 27 Jan 2025 13:55:44 GMT

Hi Vignesh,

It appears that we have been using the wrong path to find modem_socket.h. It is not located in zephyr/subsys/net/lib/sockets, but in zephyr/drivers/modem.

Please change the path accordingly.

Hieu

RE: Modify zephyr's Driver with out of tree procedure

Hieu — Thu, 23 Jan 2025 22:56:25 GMT

Hi Vignesh,

Let me try to reproduce your issue and I will follow up with you in 1 or 2 workdays.

Hieu

RE: Modify zephyr's Driver with out of tree procedure

Vignesh R — Wed, 22 Jan 2025 15:58:06 GMT

Hello Hieu,

I tried putting this line in my drivers/modem/CMakeLists.txt file (available in line no.16 of the cmakelists I gave above)

Now as u suggested I tried putting it in my drivers/CMakeLists.txt too, but ended up with same error

attaching my drivers/CMakeLists.txt

devzone.nordicsemi.com/.../1731.CMakeLists.txt

RE: Modify zephyr's Driver with out of tree procedure

Hieu — Wed, 22 Jan 2025 14:37:37 GMT

Hi Vignesh,

It seems that from NCS v2.6.0, Zephyr was changed in a way that internal headers are not readily available to external modules, which I think is a good thing.

Can you try adding this to the driver's CMakeLists.txt?

zephyr_library_include_directories_ifdef(CONFIG_NET_SOCKETS ${ZEPHYR_BASE}/subsys/net/lib/sockets)

Hieu