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Lab Session 6-II: Multitasking with FreeRTOS

Estimated time: 1.5 h (1 session)

1. Working with real hardware

1.1 Test the IMU (inertial sensor)

Read and run the program IMU.ino to understand how to work with the M5Core2 sensor.

1.2 Test the vibration motor

Read and run the program vibration.ino to understand how to work with the actuator on the M5Core2.

1.3 Multitasking with sensor and actuator

Create a sketch for the M5Core2 using FreeRTOS that does the following:

  1. Use 4 tasks. Initially all tasks run on core 0.
  2. Task 1 monitors button presses for buttons A, B and C. It has priority 2 and runs at 100 Hz.
  3. Task 2 writes IMU data to the M5 screen similarly to the program IMU.ino. In this case, the data are displayed only when button B has been pressed. If pressed again, the screen remains in its current state (data are not updated). Pressing B again resumes updates, and so on. This task has priority 1 and runs at 25 Hz.
  4. Task 3 triggers a vibration pattern as an alarm if acceleration magnitude reaches or exceeds 2 G (sqrt(accXaccX + accYaccY + accZ*accZ) > 2). The pattern should make the motor vibrate 5 times with 200 ms intervals. This task has priority 3 and runs at 5 Hz.
  5. The final task writes to the serial port every change that occurs in the application. It only writes if an event has occurred (button A, B or C press, or a vibration alarm). This task has priority 0 and runs at 10 Hz. The published data are:
  6. How many times A has been pressed.
  7. How many times C has been pressed.
  8. If B has been pressed and IMU data are currently being displayed, write: "Using IMU data". Otherwise write: "Not using IMU data".

Question

Since the device has 2 cores, you could distribute tasks between them to balance load. For the tasks above: - which task(s) would you assign to each core and why? - Try running the program with those changes and observe any differences in behavior.

2. Working in simulation

To do this lab in simulation you can use the ESP32 with the following substitutes:

  • Three external buttons to act as buttons A, B, and C. Configure external interrupts for them.
  • For the IMU, add an external sensor. In Wokwi you can use the mpu6050 IMU. See its documentation here. Communication between the IMU and the ESP32 is done via I2C. An Arduino example is available here.
  • Wokwi does not include a vibration motor for the 2G alarm. Replace it with an LED that blinks or varies intensity using PWM duty cycle.

  • To display data on screen you have two options:

  • The simplest: send the data over the serial port.

  • If you prefer, use a TFT display similar to the M5Core2 screen (covered in the next topic). Wokwi provides an ILI9341 TFT you can use. See the documentation here. Example projects here and here.