FreeRTOS Lab 05

• Demonstrate that the scheduler always selects the highest Ready state task to run

  by using the vTaskPrioritySet() API function to change the priority of two tasks relative to each other.

• Two tasks are created at two different priorities.

  Neither task makes any API function calls that cause it to enter the Blocked state,

  • So both are in either Ready or Running state.
  • So the task with highest priority will always be the task selected by the scheduler to be in Running state

• Expected Behavior
  1. Task 1 is created with the highest priority to be guaranteed to run first. Task 1 prints out a couple of strings before raising the priority of Task 2 to above its own priority.
  2. Task2 starts to run as it has the highest relative priority.
  3. Task 2 prints out a message before setting its own priority back to below that of Task 1.
  4. Task 1 is once again the highest priority task, so it starts to run and forcing Task 2 back into the Ready state.

• Functions to be Used
  1. vTaskPrioritySet(xTaskHandle pxTask, unsigned portBASE_TYPE uxNewPriority);

     To be used to change the priority of any task after the scheduler has been started.

     Available if INCLUDE_vTaskPrioritySet is set 1.

     Two parameters

     pxTask: Handle of the task whose priority is being modified. A task can change its own priority by passing NULL in place of a valid task handle.

     uxNewPriority: the priority to be set.

  2. unsigned portBASE_TYPE uxTaskPriorityGet(xTaskHandle pxTask);

     To be used to query the priority of a task

     Available if INCLUDE_vTaskPriorityGet is set 1

     pxTask: Handle of the task whose priority is being modified. A task can query its own priority by passing NULL in place of a valid task handle.

     Returned value: the priority currently assigned to the task being queried