In this tutorial we will be looking all the possible freeRtos configuration.
Contents
Task States
In the FreeRTOS a task can be in either of four different states viz., Running, Ready, Blocked and Suspended as shown in below image.
1.Running: The task which is executing currently is said to be in running state. It owns the CPU.
2.Ready: The task which is neither suspended nor blocked but still not executing will be in ready state. It's not in running state because either a high priority or equal priority task is executing.
3.Blocked: A task will go in blocked state whenever it is waiting for an event to happen. The event can be completing a delay period or availability of a resource. The blocked tasks are not available for scheduling.
4.Suspended: When vTaskSuspend() is called, the task goes in suspended state. It can be resumed by calling xTaskResume(). The suspended tasks are also not available for scheduling.
API Details
Here we will discuss some of the most frequently used APIs related to tasks.
1.xTaskCreate(): This interface is used to create a new Task, if the task is successfully created then it returns pdPass(1) or else errCOULD_NOT_ALLOCATE_REQUIRED_MEMORY(-1). Check this link for more details.
2.xTaskDelay(): This function is used to delay/block the task for specified delay time(ticks). INCLUDE_vTaskDelay needs to be set to 1 in FreeRtosConfig.h file for using this function. Check this link for more details.
Example1
In this example, we are going to create 3-Tasks with different priorities.
Each task will run for some time and then goes to blocked state allowing the other tasks to run. Once the waiting time is elapsed the scheduler will bring the task to ready state and eventually run state if its priority is higher compared to the currently running task.
Output
The controller starts the exceution from setup functions. The Serial port is initially at 9600 baud rate after whihc a message is printed.
After 3-Tasks(Task1,Task2 and Idle) are created in order. At the end of the Setup function, scheduler/kernel take the control.
Since Task2 has the highest priority it will run first and goes to block state for 50ms. Now 2-tasks are availbale for scheduler and it chooses Task1 as it is the available hicgher priority task.
Now Task1 runs for some time and then goes to blocked state and cpu is left out with only Idle task and it starts running.
After Task2 waiting time is elapsed, it comes to Ready state. Since it has got hicgher priority compared to Idle task, it will preempt Idle task and Task Starts running.