MQTT Testing Program and Development

13.6.5 MQTT Testing Program Lab Experiment

Place mqtt_test and paho.mqtt.c.tar.bz2 in the same directory on Ubuntu.

1. Compile the Paho Library

Execute the following commands in Ubuntu:

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$ tar xjf paho.mqtt.c.tar.bz2
$ cd paho.mqtt.c

Edit CMakeLists.txt and add the following content at the top:

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set(CMAKE_SYSTEM_NAME Linux)
set(CMAKE_SYSTEM_PROCESSOR arm)
SET(CMAKE_C_COMPILER aarch64-poky-linux-gcc)
SET(CMAKE_CXX_COMPILER aarch64-poky-linux-g++)
set(CMAKE_SYSROOT /opt/remi-sdk/sysroots/aarch64-poky-linux)
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_PACKAGE ONLY)

Then execute the following commands to compile:

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$ source /opt/remi-sdk/environment-setup-aarch64-poky-linux
$ mkdir build
$ cd build
$ cmake ../ -DCMAKE_INSTALL_PREFIX=output
$ make
$ make install

If everything goes well, an output directory will be generated in the build directory (some error messages may indicate permission issues, which are not critical), containing many library files. The content is as follows:

$ ls output/bin include lib share

Copy the header files and library files to the toolchain:

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$ sudo cp -rf output/include/* /opt/remi-sdk/sysroots/aarch64-poky-linux/usr/include/
$ sudo cp -rfd output/lib/* /opt/remi-sdk/sysroots/aarch64-poky-linux/usr/lib64/

Compress the output directory and upload it to the development board:

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$ tar cjf output.tar.bz2 output/
$ scp output.tar.bz2 [email protected]:/mnt

On the development board, decompress the output.tar.bz2 file and copy the library files to /usr/lib64, using the following commands:

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# cd /mnt
# tar xjf output.tar.bz2
# cd output/lib
# cp -d libpaho* /usr/lib64/

2. Compile the Test Program

Execute the following commands in Ubuntu:

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$ source /opt/remi-sdk/environment-setup-aarch64-poky-linux
$ cd mqtt_test
$ make
$ scp mqtt_test [email protected]:/mnt

3. Testing

According to 13.6.3 Using PC MQTT Tools, first start the MQTT service software, then start MQTTX with the following configuration and connection:

In MQTTX, subscribe to messages with the topic /iot/up and send messages with the topic /iot/down, as shown in the figure below:

Finally, execute the mqtt_test program on the development board, as shown below:

13.7 MQTT Program Development

The source code is:

13.7.1 Program Flow

The program mainly has two major functions:

① Periodically read