Problems setting up PPP using SLM in NRF9151DK

RE: Problems setting up PPP using SLM in NRF9151DK

ThiSo — Tue, 13 Jan 2026 14:23:44 GMT

Hi Simon!

It turns out, the problem was hardware related. UART1 was disconnected by a colleague of mine in previous unrelated tests, and he forgot to connect it back again...

Now the test on linux terminal works fine just like yours, and I could also connect it with my ESP32-S3.

Thanks a lot for your help!

RE: Problems setting up PPP using SLM in NRF9151DK

Simon D-M — Tue, 13 Jan 2026 10:22:22 GMT

Hi,

Strange..., I just retried and it still works...

To see if this is a build / firmware problem, can you try to upload my .hex file to your nRF9151 DK. It is the serial modem add-on that I built on my end.

devzone.nordicsemi.com/.../42320.merged.hex

To flash this firmware, you can use the command "nrfutil device program --firmware /path/to/merged.hex". (You may need to use "nrfutil device recover" if you see an error stating that the application core is protected.)

Also, Just to be sure, can you please confirm with the cellular monitor that your device is indeed connected to the network before making the PPP connection ?

Best regards,

Simon D-M

RE: Problems setting up PPP using SLM in NRF9151DK

ThiSo — Mon, 12 Jan 2026 19:26:50 GMT

Hello again!

I downloaded nRF Connect for VSCode and the newest SDK/Toolchain available, and also cloned the Serial Modem addon to the SDK workspace.

Even so, my problem still stands and I'm not able to make it work even with the latest test guide (which had some different steps compared to the one I previously refered to).

Below, prints of my build configuration and the test done using nRF Connect and linux terminal:

RE: Problems setting up PPP using SLM in NRF9151DK

Simon D-M — Thu, 08 Jan 2026 15:18:43 GMT

Hi,

[quote user="ThiSo"]My modem firmware version is also v2.0.3, but I don't really know where to get the SLM version. Using AT#XSLMVER I only get #XSLMVER: "3.1.99","3.2.0-cellular-e91806dc2b3f", that is the ncs version and modem library version.[/quote]

To get the latest Serial Modem addon you can follow this guide (link).

[quote user="ThiSo"]I don't seem to have this file in the project directory. Could you please send its contents so I can create it and replace slm-uart.overlay to see if that's the problem?[/quote]

Here is the file from the Serial Modem addon GitHub (link).

[quote user="ThiSo"]I will also try updating ncs and integrating it with VSCode like yours.[/quote]

Here is our page for nRF Connect For VS Code (link).

Best regards,

Simon D-M

RE: Problems setting up PPP using SLM in NRF9151DK

ThiSo — Thu, 08 Jan 2026 14:55:33 GMT

Hello Simon, thanks for the answer!

[quote userid="148570" url="~/f/nordic-q-a/126419/problems-setting-up-ppp-using-slm-in-nrf9151dk/558283"]Which version of the Serial Modem addon (previously called Serial LTE Modem - SLM) and which modem firmware are you using ? I used the latest Serial modem addon and the mfw 2.0.3[/quote]

My modem firmware version is also v2.0.3, but I don't really know where to get the SLM version. Using AT#XSLMVER I only get #XSLMVER: "3.1.99","3.2.0-cellular-e91806dc2b3f", that is the ncs version and modem library version.

[quote userid="148570" url="~/f/nordic-q-a/126419/problems-setting-up-ppp-using-slm-in-nrf9151dk/558283"]I think you are missing overlay-ppp-without-cmux.conf in your build config.[/quote]

I don't seem to have this file in the project directory. Could you please send its contents so I can create it and replace slm-uart.overlay to see if that's the problem?

I will also try updating ncs and integrating it with VSCode like yours.

RE: Problems setting up PPP using SLM in NRF9151DK

Simon D-M — Thu, 08 Jan 2026 13:50:40 GMT

Hi,

I tried on my end (without your slm-uart.overlay), and it is working.

Which version of the Serial Modem addon (previously called Serial LTE Modem - SLM) and which modem firmware are you using ? I used the latest Serial modem addon and the mfw 2.0.3

[quote user=""]I built and flashed the modem with configuration files to enable it using the following command:

west build -b nrf9151dk/nrf9151/ns nrf/applications/serial_lte_modem -- -DCONF_FILE="prj.conf;overlay-ppp.conf" -DDTC_OVERLAY_FILE="overlay-ppp-without-cmux.overlay;slm-uart.overlay"[/quote]

I think you are missing overlay-ppp-without-cmux.conf in your build config.

Here is the build config I used :

Best regards,

Simon D-M