SLM connected to external MCU, no response via UART2

[Mark H]

Hi!

I have previously tested connecting the nRF9160-DK to an external MCU to act as an Serial LTE Modem as per the application description. And it worked

fine. Since then I've been doing other tests with the DK and now when trying the SLM connected to external MCU via UART2 it does not work at all.

I've tested the external MCU and a serial adapter connected to the TX/RX ports sending simple AT commands, but I get no response back from the DK.

No OKs or ERRORs which I did get previously. I have built the SLM application in SES for UART0 (USB) and UART2 separately and I get the expected

results via UART0 but nothing via UART2.

I have reprogrammed the board controller FW since the first test, but I'm not sure if it might have affected anything.

Configuration:

• nRF9160-DK with MFW 1.3.0
• NCS v.1.6.0
• Changes to prj.conf for SLM:
  • CONFIG_UART2_NRF_HW_ASYNC_TIMER=2 
  • CONFIG_SLM_CONECT_UART_2=y
• Built with SES

Any guidance would be very appreciated!

[Carl Richard]

Hi, Mark!

Thanks for reaching out. Have you made sure to configure the setup as described in Connecting with an external MCU? Make sure that the correct baud rate and pins are used. 

Please share the nRF9160DK logs as well. These can be read out in the Segger Embedded Studio debug terminal, or by using the Segger RTT viewer application.

Best regards,
Carl Richard

[Mark H]

Thank you for your reply. Yes I have confirmed that the setup is correct. I do not use HWFC though.
I do not seem to get any log output even though they are disabled:

*** Booting Zephyr OS build v2.6.0-rc1-ncs1  ***
I: Starting bootloader
I: Primary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
I: Secondary image: magic=unset, swap_type=0x1, copy_done=0x3, image_ok=0x3
I: Boot source: none
I: Swap type: none
I: Bootloader chainload address offset: 0x10000
I: Jumping to the first image slot

I tested the SLM connected to PC via USB and while it works I also do not get any log ouput

[Carl Richard]

 Hello again!

Seems like some extra logging must be enabled. Could you add CONFIG_SLM_LOG_LEVEL_DBG=y in prj.conf and see if the output changes then? 

If possible, please check if there are any activity on the UART lines using a oscilloscope or logic analyzer.

Best regards,
Carl Richard

[Mark H]

Strange, I've enabled the log output but I don't get any logs at all. There is probably something wrong on my system then. I should be able to solve that myself if that's the case.

Also I tested with an oscilloscope on both the TX/RX pins but I did not receive anything on the RX pin.

I will try building the project on another system and perhaps get hold of another DK. We should have a few extra somewhere... Thank you for your help though!

[Carl Richard]

Hello!

That is indeed very strange. Please keep me updated! 

Best regards,
Carl Richard