LTE link monitor not accepting any AT commands after publishing to mqtt broker in data mode with nrf9160DK and SLM

[ericlestor]

Hi,

after connecting to our mqtt broker I set nrf9160DK to data mode and publish data to our mqtt broker:

AT#XMQTTCON=1,"xxx","xxx","xxx","xxx.xxx.com",1883
OK
#XMQTTEVT: 0,0
AT#XMQTTPUB="xxx/status/1_2"
OK
test+++
#XMQTTMSG: 23,9
eecfc1b1fb5b/status/1_2
#XMQTTEVT: 2,0

After this LTE link monitor is not accepting any AT commands. It keeps receiving mqtt connection ping though: #XMQTTEVT: 9,0

Here is RTT log of SLM:

00> [00:00:00.497,924] <inf> slm: Serial LTE Modem
00> [00:00:00.598,724] <inf> slm_at_host: at_host init done
00> [00:01:28.139,709] <inf> slm_at_host: Enter datamode
00> [00:01:36.501,831] <inf> slm_at_host: time limit reached
00> [00:01:36.501,892] <inf> slm_at_host: Raw send 9
00> [00:01:36.508,483] <inf> slm_mqtt: datamode send: 0

how do I get back to normal mode where I can send AT commands again?

[Håkon Alseth]

Hi,

 

When omitting the payload in the AT#XMQTTPUB call, SLM will enter datamode, as per the documentation:

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/2.1.0/nrf/applications/serial_lte_modem/doc/MQTT_AT_commands.html#mqtt-publish-xmqttpub

 

When using datamode, I would recommend that you use another terminal, like realterm/teraterm/putty.

LTE Link Monitor adds linebreaks to each string, which will cause problems with data mode.

 

Kind regards,

Håkon

[ericlestor]

I can't write anything on putty or teraterm, nothing showing on terminal when i write, just "ready" when nrf9160 is reset, i.e. putty:

But this isn't really the issue, I just want to know how to exit data mode. I am also using external MCU(nrf52840) with nrf9160dk and trying to publish to our mqtt broker, it publishes ok, but never exits the data mode. So whatever I write to uart after initially entering data mode are published to our mqtt broker and not handled as At commands.

[Håkon Alseth]

The default exit command out of datamode is "+++", ie only these 3 bytes. You can change this if you want, via CONFIG_SLM_DATAMODE_TERMINATOR.

Putty probably has a different line-ending as compared to the default in SLM (which is CR+LF). You can change this by modifying either the putty settings, or the SLM firmware (CONFIG_SLM_CR_TERMINATION=y)

 

Kind regards,

Håkon

[ericlestor]

I just can't get it to work with my external MCU (nrf52840). Is this supposed to work with FIFO aswell or do I need to change my uart connection? Here is my code:

void uart_init(void)
{
    uint32_t err_code;
    app_uart_comm_params_t const comm_params =
        {
            .rx_pin_no = UART_RX,
            .tx_pin_no = UART_TX,
            .rts_pin_no = NRF_UART_PSEL_DISCONNECTED,
            .cts_pin_no = NRF_UART_PSEL_DISCONNECTED,
            .flow_control = APP_UART_FLOW_CONTROL_DISABLED,
            .use_parity = false,
            .baud_rate = NRF_UART_BAUDRATE_115200

        };
    APP_UART_FIFO_INIT(&comm_params,
        UART_RX_BUF_SIZE,
        UART_TX_BUF_SIZE,
        uart_event_handle,
        APP_IRQ_PRIORITY_LOWEST,
        err_code);
    APP_ERROR_CHECK(err_code);
}

int8_t send_at_command(char *at_command)
{
    while(!uart_tx_empty);
    for (int i = 0; i < strlen(at_command); i++)
    {
        uint32_t retval = app_uart_put(at_command[i]);
        if (retval != 0)
        {
            app_uart_flush();
            return -1;
        }
    }
    if(strstr(at_command, "+++") == NULL)
    {
        app_uart_put('\r');
        app_uart_put('\n');
    }
    uart_tx_empty = false;
    return 0;
}

[Håkon Alseth]

Hi,

 

Which pins are being used on both sides?

 

The default pinout of the nRF9160 uart0 is routed directly to the SEGGER IC, and not the pin lists. You'll need to change the SLM config to use other pins, as shown in the documentation:

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/applications/serial_lte_modem/doc/slm_description.html#connecting-with-an-external-mcu

 

Kind regards,

Håkon

[ericlestor]

The uart communication works fine (pins are nrf52840 RX =p0.15, TX = p0.16, nrf9160dk RX=p0.11, TX=p0.10) , that is not the issue. I just can't get the nrf9160 to exit the datamode.

[Håkon Alseth]

Hi,

 

ericlestor said:

I just can't get the nrf9160 to exit the datamode.

You should not need to append "\r\n" to exit datamode, "+++" shall be enough.

Do all other AT commands work as expected, including the responses provided back from the nRF9160?

 

Did you try this with a terminal to see if datamode works as expected there?

 

Kind regards,

Håkon

[ericlestor]

Other commands work fine, including the responses. I couldn't get either teraterm or putty to send anything to nrf9160DK. Couldn't write anything to terminal, neither program accepted any typing to terminal.

EDIT: Realterm works fine, also exits data mode. I am beginning to think that there is something wrong with my code. I will do more tests later.

Thanks for your support and I will contact you again if I still cannot get my code to work.

[ericlestor]

Yes, the problem was with my code, it exited and entered back to datamode immediately. Sorry to have wasted your time and thanks again for your continued support.