FreeRTOS Exercise Lab20

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 */
    portYIELD_FROM_ISR(xSW1Yield);
}

How It Works …