FreeRTOS Exercise Lab20

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FreeRTOS Exercise Lab20 - Deferred Interrupt Processing

  1. Create Task 1 as a continuous processing task, and Task 2 (interrupt handler task) as the task to which interrupt processing is deferred.
    In Task 1, display "Task 1 is Running."
  2. Install an Interrupt handler for SW1 Button switch (GPIO PortF)
    There are two user push buttons on the EK-TM4c123GXL LaunchPad Board.
  3. Display "You Pressed SW1 Button switch" in the Task 2 whenever SW1 is pressed

Note: Task2 should be higher priority than Task1

  • If the interrupt processing is particularly time critical, then the priority of the deferred processing task can be set to ensure the task always pre-empts the other tasks in the system. The ISR can then be implemented to include a call to portYIELD_FROM_ISR(), ensuring the ISR returns directly to the task to which interrupt processing is being deferred.

Code Snippets

/* Task 1 is continuous processing Task */
void vTask1(void *pvParameters)
    for(;;) {
        printf("%s", "Task1 is Running.\n\r");
        for(volatile auto uint32_t ul = 0; ul < 0xffff; ul++ ){ ; }
/* Deferred interrupt processing Task */
void vTask2(void *pvParameters)
    for(;;) {
        vTaskSuspend(NULL);                /* Wait for SW1 interrupt */
        printf("%s", "You Pressed SW1 Button switch\n\r");
/* PortF Interrupt Service Routine */
void vGPIO_PortF_ISR(void)
    BaseType_t xSW1Yield;
    GPIO_PORTF_ICR_R = 0x10;               /* clear PF4 int */
    xSW1Yield = xTaskResumeFromISR(hPortF); /* hPortF is Handle of vTask2 */

How It Works ...

Freertos int process in high priorit task.png