Difference between revisions of "Embedded System Tutorial File I/O"

Revision as of 14:09, 18 March 2016

In this project, we will attempt to "combine" all the FreeRTOS knowledge into a single assignment.

After completing the assignment, you will get a sense of how the CPU is utilized, and how to use a new FreeRTOS event group API. All together, you should achieve a better sense of designing your tasks and using the File I/O for debugging purposes.

Assignment

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.