serial_lte_modem stops responding when you send an empty line

[Georgi Valkov]

The serial_lte_modem sample is heavily broken. Unlike the AT client sample which simply works with PuTTY out of the box, for the serial_lte_modem you need to configure PuTTY, Terminal, Keyboard to CR LF. Then it will accept commands until you send an empty line. Once you do that, it will not replay to any further commands until you power cycle the board. On top of that I cannot send PING or connect to anything, even though my Thingy:91 is registered to an NB-IoT network, and has a valid and enabled IP address context. What is the proper syntax of those proprietary AT commands? There is no description on the Infocenter for AT commands, so I used whatever scarce resources there are on the serial_lte_modem page.

While I hear comments that I should not expect different samples to operate likewise, the fact is that they are so inconsistent that you need to have different setting in every single one and each has its own quirks and problems. And if you choose to automate the AT commands over BLE, things get even worse.

[Didrik Rokhaug]

Hi, and sorry for your bad experience with the serial_lte_modem.

 

Unlike the AT client sample which simply works with PuTTY out of the box, for the serial_lte_modem you need to configure PuTTY, Terminal, Keyboard to CR LF.

 Yes, as explained in the documentation: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.3.0/nrf/applications/serial_lte_modem/README.html#terminal-connection

You can, however, change the terminating character by setting either of the following options to "y" in the prj.conf file:

- CONFIG_SLM_NULL_TERMINATION

- CONFIG_SLM_CR_TERMINATION

- CONFIG_SLM_LF_TERMINATION

- CONFIG_SLM_CR_LF_TERMINATION (default)

 

hen it will accept commands until you send an empty line. Once you do that, it will not replay to any further commands until you power cycle the board.

 This is, unfortunately, a known issue we are working on resolving. For now, don't send empty lines, or commands terminated by an interleaving sequence of carriage-returns and linefeeds. I.e. an "\r\r\r\r\n\n\n\n" ending is ok because the carriage-returns and linefeeds are not "mixed", while "\r\n\r" is not ok.

 

On top of that I cannot send PING or connect to anything, even though my Thingy:91 is registered to an NB-IoT network, and has a valid and enabled IP address context. What is the proper syntax of those proprietary AT commands? There is no description on the Infocenter for AT commands, so I used whatever scarce resources there are on the serial_lte_modem page.

 As the example adds more AT commands that are handled by the application, and not the modem, the AT command documentation in the infocenter is not the right place to look. That documentation only describes the commands supported by the modem. Instead, the added AT commands are documented in the sample documentation. We are aware that the sample documentation is a bit lacking, and are working on improving that.

As for why your commands are not working, it looks to me like you have done everything correctly, except for missing double-quotes around the strings. I.e. the #XPING command should be

AT#XPING="httpstorm.com",32,1000,4,1000

Best regards,

Didrik

[Georgi Valkov]

Thank you very much, Didrik!

The ping works now.