Simplest possible MQTT-SN client demo for MCUs without any network interface. MCU sends MQTT-SN "quick publish" (QoS -1) packets over a serial (SLIP) connection.

Tested on STM32F103C8 (aka the "Blue Pill") but should be easily portable to any board supported by the Arduino library.

This project uses PlatformIO for building.

Connect your Pill to an ST-LINK and run:

$ pio run -t upload

You can configure some options in include/app_config.h and platformio.ini files.

1. Default: just use Pill's native USB as a SLIP interface.

2. Using Serial1 and Serial2 (must be enabled in platformio.ini)

• SLIP TX = PA9
• SLIP RX = PA10
• DBG TX = PA2
• DBG RX = PA3

Connect your Pill USB to a Linux computer and run:

$ sudo slattach -L -s 115200 -p slip -d /dev/ttyACM0

And in another terminal:

$ sudo ifconfig sl0 192.168.100.1 dstaddr 192.168.100.2
$ ping 192.168.100.2

The LED on the pill should blink with every received packet. Pill detects the echo request packets but does not send echo reply so you will see "100% packet loss" in ping, that's ok.

If everything went well, you can start an MQTT-SN gateway (e.g. this one ) on 1883/udp, configure predefined topic 1 and you should see Hello! messages sent by the Pill on the configured topic.