Difference between revisions of "Embedded System Tutorial FreeRTOS"

Revision as of 19:31, 5 February 2014

The objective of this assignment is to show you how to create a FreeRTOS task a few different ways. The FreeRTOS tutorial is definitely a must read before going through this lesson.

FreeRTOS "Hello World" Task

A task just needs memory for its stack and and infinite loop. To prevent "hogging" the CPU, you should use a delay such that the CPU can be allocated to other tasks. Here is the simplest FreeRTOS task:

void hello_world_task(void* p)
{
    while(1) {
        puts("Hello World!");
        vTaskDelay(1000);
    }
}

int main()
{
    xTaskCreate(hello_world_task, (signed char*)"task_name", STACK_BYTES(2048), 0, 1, 0);
    vTaskStartScheduler();

    return -1;
}

C++ based FreeRTOS task

As a project gets more complex, it becomes difficult to manage initialization and share queue or semaphore handles. This was the motivation to create a C++ based FreeRTOS task.

Assignment

This assignment is based on SJ-One board, but you can alter the requirement to fit your own hardware.

1. Create a task (task1) that computes the orientation of the board.

   Send the orientation enumeration, such as "up", "down", "left", "right" to a queue

2. Create another task (task2) that waits on the queued item

   If the orientation is left or right, light up the LEDs (otherwise turn them off)

3. Create a terminal task with a command "orientation on" and "orientation off"

   If orientation is commanded on, resume the task1, otherwise suspend it

   See code below on hints of how this command can get control of another task.

// At the terminal tasks taskEntry() function :
bool terminalTask::taskEntry()
{
    // Add the command, but pass the "this" pointer when the command is invoked
    cp.addHandler(orientationCmd,  "orientation", "Two options: 'orientation on' or 'orientation off'", this);
}

// Somewhere else:
CMD_HANDLER_FUNC(orientationCmd)
{
    // Our parameter was the terminal task's "this" pointer:
    scheduler_task *terminalTask = (scheduler_task*) pDataParam;

    // Use this to get the pointer of the "other task"
    scheduler_task *orientTask = terminalTask->getTaskPtrByName("orientTask");

    // We've got the handle now, so use FreeRTOS API to suspend or resume
    if (cmdParams == "on") {
        vTaskResume(orientTask->getTaskHandle());
    }
    else {
        vTaskSuspend(orientTask->getTaskHandle());
    }
}