SLM Shell issue on nRF52840dk and nRF9151DK SLM

RE: SLM Shell issue on nRF52840dk and nRF9151DK SLM

Øyvind — Fri, 12 Dec 2025 08:13:51 GMT

Hi Roya,

[quote user="_rd"]I re-installed the SDK, toolchain, and SEGGER, running more tests. The SLM-shell seems to work as expected, please see the logs below:[/quote]

Thanks for the information. Looks like this has solved the issue with UART between the devices at least.

[quote user="_rd"]However, no changes on the RTT viewer, same results as my last post. I tried both J-Link v8.88 and v8.76.[/quote]

This is strange. One thing that our developers point to is to test with the newest Serial Modem application. This is the newest official application we´ll be using going forward: Serial Modem application for nRF91-based devices. Could you give that a try? The Serial LTE Modem is now deprecated in v3.2.0 in nRF Connect SDK.

[quote user="_rd"]

I was wondering if I can use uart backend instead of RTT, but I am confused which uart peripheral is used for this option, if it is uart0, how TX/RX on pins 11 and 12 are sent to console?

[/quote]

Have a look at this documentation on Logging. It should be possible to use UART instead of RTT.

Kind regards,
Øyvind

RE: SLM Shell issue on nRF52840dk and nRF9151DK SLM

_rd — Wed, 10 Dec 2025 15:46:25 GMT

Hello Øyvind,

I re-installed the SDK, toolchain, and SEGGER, running more tests. The SLM-shell seems to work as expected, please see the logs below:

However, no changes on the RTT viewer, same results as my last post. I tried both J-Link v8.88 and v8.76.

- I was wondering if I can use uart backend instead of RTT, but I am confused which uart peripheral is used for this option, if it is uart0, how TX/RX on pins 11 and 12 are sent to console?

Can you please clarify it?

Thanks,

Roya

RE: SLM Shell issue on nRF52840dk and nRF9151DK SLM

_rd — Tue, 09 Dec 2025 19:37:44 GMT

Hello Øyvind,

Thank you for providing the build configurations.

I have double-checked all connections, also recreated new applications for both, but still stuck.

- SLM_shell TX aborts:

- As for SLM, I am not receiving the Ready message after toggling the power pin:

It seems J-link RTT is somehow disconnected, can't figure out the reason.

Regards,

Roya

RE: SLM Shell issue on nRF52840dk and nRF9151DK SLM

Øyvind — Tue, 09 Dec 2025 10:24:57 GMT

Hello Roya,

[quote user=""][00:01:23.960,601] <wrn> mdm_slm: UART_TX_ABORTED, dropped: 4 bytes
uart:~$ [00:01:33.860,687] <err> mdm_slm: timeout[/quote]

I was able to reproduce this issue. But on my side it turned out to be wrong wiring. Double checked my wires and had flipped rx and tx on one side. Now I can send the command slm at and get response OK. Also, slmsh powerpin works as expected.

uart:~$ > slmsh powerpin
slmsh powerpin
uart:~$ [00:12:25.233,245] <inf> mdm_slm: Enable power pin
[00:12:25.333,404] <inf> mdm_slm: Disable power pin
s> slm at
lm at
[00:12:33.742,950] <wrn> mdm_slm: UART_TX_ABORTED, dropped: 4 bytes
> slmsh powerpin
uart:~$ slmsh powerpin
uart:~$ [00:12:43.643,005] <err> mdm_slm: timeout
[00:12:43.645,233] <inf> mdm_slm: Enable power pin
[00:12:43.745,361] <inf> mdm_slm: Disable power pin
[00:12:44.954,803] <inf> app: Data received (len=7): Ready

> slm at
slm at
Ready

OK

Here is my build configuration in VS Code for both projects:

SLM

SLM Shell

Kind regards,
Øyvind

RE: SLM Shell issue on nRF52840dk and nRF9151DK SLM

_rd — Mon, 08 Dec 2025 13:47:57 GMT

Hello,

I built the serial LTE modem with this configuration:

However, I had issues with building SLM_Shell application.

I was assuming it would automatically merge nrf52840dk_nrf52840.conf with prj.conf, but it didn't. I received error regarding SLM_POWER_PIN which by default is -1 and in that file assigned to pin 11.

I had to copy the content of that file to prj.conf to avoid the error, so the new prj.conf was:

CONFIG_STACK_SENTINEL=y

CONFIG_MAIN_STACK_SIZE=4096

CONFIG_HEAP_MEM_POOL_SIZE=8192

CONFIG_SYSTEM_WORKQUEUE_STACK_SIZE=2048

CONFIG_LOG=y

CONFIG_LOG_BACKEND_UART=y

CONFIG_CONSOLE=y

CONFIG_UART_CONSOLE=y

CONFIG_SHELL=y

CONFIG_SHELL_WILDCARD=n

CONFIG_SHELL_ARGC_MAX=40

CONFIG_SHELL_CMD_BUFF_SIZE=1024

CONFIG_SHELL_STACK_SIZE=2048

CONFIG_SHELL_LOG_BACKEND=y

CONFIG_SERIAL=y

CONFIG_UART_ASYNC_API=y

CONFIG_MODEM_SLM=y

CONFIG_MODEM_SLM_SHELL=y

CONFIG_MODEM_SLM_LOG_LEVEL_INF=y

CONFIG_ASSERT=y

CONFIG_NRFX_UARTE1=y

CONFIG_UART_1_INTERRUPT_DRIVEN=n

CONFIG_UART_1_ASYNC=y

CONFIG_MODEM_SLM_POWER_PIN=11

CONFIG_MODEM_SLM_INDICATE_PIN=13

Regards,

Roya

RE: SLM Shell issue on nRF52840dk and nRF9151DK SLM

Øyvind — Mon, 08 Dec 2025 13:33:16 GMT

Thanks for clarifying. I´m having issues with building this project out of the box. Could you please provide the steps you used to build serial LTE modem application? Did you build with -DDTC_OVERLAY_FILE="overlay-external-mcu.overlay"?

Kind regards,
Øyvind

RE: SLM Shell issue on nRF52840dk and nRF9151DK SLM

_rd — Fri, 05 Dec 2025 13:48:54 GMT

Hello,

Thanks for your prompt reply.

I am following the guide in 'Connecting with an external MCU' in the above link, please see below the connection between boards:

nRF52 Series DK	nRF91 Series DK
UART TX P1.02	UART RX P0.11
UART RX P1.01	UART TX P0.10
UART CTS P1.06	UART RTS P0.12
UART RTS P1.07	UART CTS P0.13
GPIO OUT P0.11	GPIO IN P0.31
GPIO IN P0.13	GPIO OUT P0.30
GPIO GND	GPIO GND

I have changed the config to:

CONFIG_SLM_POWER_PIN=31

CONFIG_SLM_INDICATE_PIN=30

No changes on the original codes, uart2 on nRF9151 and uart1 on nRF52840 are used as ncs-slm-uart.

Regards,

Roya

RE: SLM Shell issue on nRF52840dk and nRF9151DK SLM

Øyvind — Fri, 05 Dec 2025 13:35:49 GMT

Hello, could you please provide more information on you connection between the nRF9151DK and nRF52840?

I will try to reproduce the issue on my side.

Kind regards,
Øyvind