Support MAVLink console

Implement receiving and sending SERIAL_CONTROL message
Use global defined print function instead of Serial.printf

docs/build.md

@@ -191,6 +191,12 @@ You can adjust some of the drone's parameters (include PID coefficients) in QGro
 
 <img src="img/parameters.png" width="400">
 
+#### CLI access
+
+In addition to accessing the drone's command line interface (CLI) using the serial port, you can also access it with QGroundControl using Wi-Fi connection. To do that, go to the QGroundControl menu ⇒ *Vehicle Setup* ⇒ *Analyze Tools* ⇒ *MAVLink Console*.
+
+<img src="img/cli.png" width="400">
+
 > [!NOTE]
 > If something goes wrong, go to the [Troubleshooting](troubleshooting.md) article.
 

docs/troubleshooting.md

@@ -14,7 +14,7 @@ Do the following:
 * **Check the battery voltage**. Use a multimeter to measure the battery voltage. It should be in range of 3.7-4.2 V.
 * **Check if there are some startup errors**. Connect the ESP32 to the computer and check the Serial Monitor output. Use the Reset button to make sure you see the whole ESP32 output.
 * **Make sure correct IMU model is chosen**. If using ICM-20948 board, change `MPU9250` to `ICM20948` everywhere in the `imu.ino` file.
-* **Check if the CLI is working**. Perform `help` command in Serial Monitor. You should see the list of available commands.
+* **Check if the CLI is working**. Perform `help` command in Serial Monitor. You should see the list of available commands. You can also access the CLI using QGroundControl (*Vehicle Setup* ⇒ *Analyze Tools* ⇒ *MAVLink Console*).
 * **Configure QGroundControl correctly before connecting to the drone** if you use it to control the drone. Go to the settings and enable *Virtual Joystick*. *Auto-Center Throttle* setting **should be disabled**.
 * **Make sure you're not moving the drone several seconds after the power on**. The drone calibrates its gyroscope on the start so it should stay still for a while.
 * **Check the IMU is working**. Perform `imu` command and check its output: