nRF9160, Using JSON in MQTT command AT#XMQTTPUB

RE: nRF9160, Using JSON in MQTT command AT#XMQTTPUB

Didrik Rokhaug — Wed, 09 Mar 2022 12:42:02 GMT

I see you have opened a new ticket where you have provided more information: https://devzone.nordicsemi.com/f/nordic-q-a/85605/nrf9160-sending-messages-via-mqtt-larger-than-256-bytes

Let's close this one, and continue the conversation there.

RE: nRF9160, Using JSON in MQTT command AT#XMQTTPUB

Stas Jis — Tue, 08 Mar 2022 12:19:41 GMT

Dear Didrik,
I was able to send JSON in "date mode" and Qos = 1.
However, I found that there is a limit on the length of the message body (256 bytes). Messages come to the broker divided into pieces of 256 bytes + the rest.

RE: nRF9160, Using JSON in MQTT command AT#XMQTTPUB

Didrik Rokhaug — Tue, 08 Mar 2022 10:20:09 GMT

You need to add the QoS parameter to the command:

AT#XMQTTPUB="Rigel/ToServer/v2/Operational","",1

RE: nRF9160, Using JSON in MQTT command AT#XMQTTPUB

Stas Jis — Mon, 07 Mar 2022 14:10:34 GMT

Didrik, Thank for the help.
Your instructions helped, JSON reached the server.

AT#XMQTTPUB="Rigel/ToServer/v2/Operational"
{"msg":"Test Json publish"}
+++
OK

However, how did I get the publication confirmation, just like using QoS = 1:

AT#XMQTTPUB="Rigel/ToServer/v2/Operational","7b2274656d7065726174757265223a32302c2276616c7565223a38307d",1,0
OK
#XMQTTEVT: 3,0

RE: nRF9160, Using JSON in MQTT command AT#XMQTTPUB

Didrik Rokhaug — Mon, 07 Mar 2022 13:00:25 GMT

Hi,

You can enter data mode by using AT#XMQTTPUB without any data.

That way, any bytes you send over UART until you send the datamode terminator ("+++", without any <CR> or <LF> line ending) will be sent to the broker on the topic specified.

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.9.1/nrf/applications/serial_lte_modem/doc/MQTT_AT_commands.html#mqtt-publish-xmqttpub

Best regards,

Didrik

RE: nRF9160, Using JSON in MQTT command AT#XMQTTPUB

Markus Tacker (he/him) — Mon, 07 Mar 2022 12:59:25 GMT

Use AT#XMQTTPUB with message set to "" to enter data mode: github.com/.../slm_at_mqtt.c

RE: nRF9160, Using JSON in MQTT command AT#XMQTTPUB

Stas Jis — Mon, 07 Mar 2022 12:54:26 GMT

Markus,
Is there a specific scenario for working with MQTT when using "data mode"?
Right now, after connecting to the broker, I don't get any result for "AT#XSEND" and I don't understand how a direct data send can be without a command to publish data.

RE: nRF9160, Using JSON in MQTT command AT#XMQTTPUB

Markus Tacker (he/him) — Mon, 07 Mar 2022 12:35:02 GMT

Data mode puts the SLM in a state where any data you send to it is forwarded verbatim to the endpoint, until you sent the terminator.

There are example of using the data mode (albeit for other clients) here.

RE: nRF9160, Using JSON in MQTT command AT#XMQTTPUB

Stas Jis — Mon, 07 Mar 2022 12:21:30 GMT

Markus,
Maybe I misunderstood, but "data mode" is not combined with AT commands? (including AT#XMQTTPUB).
If all data in the "data mode" mode received from the MCU via the UART bus is considered arbitrary, then how to organize data upload and use MQTT without changing the "Serial lte modem" firmware code.
Maybe there is some example?

RE: nRF9160, Using JSON in MQTT command AT#XMQTTPUB

Markus Tacker (he/him) — Mon, 07 Mar 2022 11:41:41 GMT

Yes, you could use the data mode: developer.nordicsemi.com/.../slm_data_mode.html

RE: nRF9160, Using JSON in MQTT command AT#XMQTTPUB

Stas Jis — Mon, 07 Mar 2022 11:26:20 GMT

Markus,
Is there any other option besides converting JSON to hexadecimal?

RE: nRF9160, Using JSON in MQTT command AT#XMQTTPUB

Markus Tacker (he/him) — Mon, 07 Mar 2022 10:23:57 GMT

See devzone.nordicsemi.com/.../nrf91-serial-lte-modem-mqtt-at-command-for-json-format