Lab Assignment: Watchdogs

Please follow the steps precisely in order to complete the objectives of the assignment. If you use the C++ FreeRTOS framework, it should make the assignment significantly easy.

  1. Create a producer task that takes 1 light sensor value every 1ms.
    • After collecting 100 samples (after 100ms), compute the average.
    • Write average value every 100ms (avg. of 100 samples) to the sensor queue.
    • Use medium priority for this task
  2. Create a consumer task that pulls the data off the sensor queue
    • Use infinite timeout value during queue receive API
    • Open a file (sensor.txt), and append the data to an output file on the SD card.
    • Save the data in this format: printf("%i, %i\n", time, light)"
    • Note that if you write and close a file every 100ms, it may be very inefficient, so try to come up with a better method such that the file is only written once a second or so...
    • Use medium priority for this task
  3. At the end of the loop of each task, set a bit using FreeRTOS event group API.
    • At the end of each loop of the tasks, set a bit using the xEventGroupSetBits()
    • Task 1 should set bit1, Task 2 should set bit2 etc.
  4. Create a watchdog task that monitors the operation of the two tasks.
    • Use high priority for this task.
    • Use a timeout of 1 second, and wait for all the bits to set. If there are two tasks, wait for bit1, and bit2 etc.
    • If you fail to detect the bits are set, that means that the other tasks did not reach the end of the loop.
    • In the event of failed to detect the bits, append a file (stuck.txt) with the information about which task may be "stuck"
    • Open the file, append the data, and close the (stuck.txt) file to flush out the data immediately.
    • Extra Credit: Every sixty seconds, save the CPU usage info to a file named "cpu.txt". See terminal command "infoHandler" for reference. Open the file, write the file, and close it immediately so the data is immediately flushed.
  5. Create a terminal command to "suspend" and "resume" a task by name.
    • "task suspend task1" should suspend a task named "task1"
    • "task resume task2" should suspend a task named "task2"
  6. Run the system, and under normal operation, you will see a file being saved with sensor data values.
    • Plot the file data in Excel to demonstrate.
  7. Suspend the producer task. The watchdog task should display a message and save relevant info to the SD card.
  8. Let the system run for a while, and note down the CPU usage in your text file.

What you created is a "software watchdog". This means that in an event when a loop is stuck, or a task is frozen, you can save relevant information such that you can debug at a later time.

You may use any built in libraries for this lab assignment.

For File I/O refer to the example here -

Back to top