Lab 5 - How to Integrate MQTT to an MPLAB® X IDE Project to Publish and Subscribe Data To/From a Cloud Broker

Follow the steps in Lab 1 and ensure you have cloned all the necessary libraries to create this thermostat MPLAB Harmony application.

To publish or subscribe the messages via the MQTT broker, it is necessary to establish Wi-Fi communication using the WIxCS02 M.2 Wireless Module Card on the SAM9X75 Curiosity wireless board by following Lab 4.

In this training module, you can learn how to connect to home or mobile Wi-Fi, read the current date from SNTP server and print it in the serial console.

Before moving to this lab, we recommend learning how to transmit the temperature value read from Temp&Hum13 Click by following to a mobile phone using Microchip Bluetooth Data (MBD) mobile application by following Lab 3.

The next step is to add RNWF WINCS MQTT services to the project graph. To do this, from wireless, launch the project graph of the project created by following Lab 4. Then, launch MPLAB Code Configurator (MCC) and from Device Resource, under Wireless > System Services, add RNWF WINCS Mqtt Service as shown in the accompanying image.

Now enable the RNWF WINCS MQTT Service in the RNWF WINCS Wi-Fi Service configuration option.

The next step is to do MQTT configurations on the SAM9X75 Curiosity Thermostat board. Configure RNWF WINCS02 MQTT configurations with the following information:

• MQTT Protocol version: v3.1.1
• Cloud Port: 1,883
• Cloud URL: broker.emqx.io
• Client Id: $MCHP/Wireless/device01
• Publish Topic Name: $MCHP/Wireless/device01
• Publish Message: Hi. It's MCHP Thermostat Device
• Sub Topic 0: $MCHP/Wireless/device02

Save and then click the Generate button. This will generate code for all the device resources that have been added in the project graph.

Up to this point, you used MCC to configure and generate code to initialize the device (SAMA9X75). All that is left is for you to do is to write the application code in the main.c and app.c file.

Documentation for each of the peripheral libraries or driver libraries can be accessed as follows:

• BSP libraries APIs can be found in bsp.h.
• For the debug peripheral libraries' APIs description and usage, see the "2.27 Debug Unit (DBGU)" page.
• MPLAB Harmony Wireless Wi-Fi- MQTT API documentation can be found ​​​​on the "1.1.18 Client - MQTT APIs" page.

In this example, you can learn how to publish/subscribe to topics using MQTT.

When the status is requested, the temperature value read using the Temp&Hum 13 Click board^TM will be broadcast from the SAM9X75 Curiosity kit.

See the example application source files, app_wincs02.c and app_wincs02.h, to connect to MQTT using M.2 WINCS02 module used in a thermostat application for reference.

APIs used for this application are as follows:

• SYS_WINCS_MQTT_SrvCtrl(SYS_WINCS_MQTT_SET_CALLBACK,...)

• SYS_WINCS_MQTT_SrvCtrl(SYS_WINCS_MQTT_CONFIG,...)

• SYS_WINCS_MQTT_SrvCtrl(SYS_WINCS_MQTT_CONNECT,...)

The source file can be downloaded and added to the project as shown:

Similarly, the header file can be added as shown:

The  app_wincs02_task should be called periodically to connect to Wi-Fi and to publish/subscribe topics via MQTT. (See the sample app.c file.)

Now, clean and build the code. (See the sample application project.)​​​​

To debug this application, follow Steps 1 through 13 of Lab 7.

Run the application from the MPLAB X IDE. Turn on the mobile hotspot/home Wi-Fi configured with:

• Username: DEMO_AP
• Password: password

The WINCS02 module will auto-detect the Wi-Fi and read the time from the SNTP server and print the debug log:

The MQTT subscribe and publish messages can also be noted in the debug log. 

To connect to MQTT, download the ​​​​MyMQTT mobile application.

On your Apple^® device, locate the App Store^® icon and download MYMQTT.

Launch the mobile application and set the parameters as shown below:

• Host: broker.emqx.io
• Port: 1883
• MQTT Protocol: MQTT V3  

The following details are needed when running the application:
The client ID of SAM9X75 Curiosity based Thermostat application device is: $MCHP/Wireless/device01, which is subscribed to the topic $MCHP/Wireless/device02.

From the MyMQTT mobile application, use the following:

• Publish
  • Topic: $MCHP/Wireless/device02 
• Subscribe
  • Topic: $MCHP/Wireless/device01 

Using the MQTT broker MyMQTT mobile application, publish the message "status" to the topic $MCHP/Wireless/device02. The SAM9X75 Curiosity, which is subscribed to this topic, receives the message, processes it and responds by publishing the real-time temperature value read from the Temp&Hum13 Click. This temperature data is then received and displayed in the dashboard of the MyMQTT mobile application, as shown:

To boot the application from a microSD card, follow these steps:

Observe the output as mentioned in the previous step.