View source for Resuming Task From ISR ← Resuming Task From ISR

[[category: Free RTOS with Arduino]]
In earlier tutorials, we saw how to Suspend and Resume the tasks from other tasks.<br>
In this tutorial, we will how to resume a task from ISR using xTaskResumeFromISR().<br>
For this, we will be using the external INTO interrupt of Arduino UNO. Check [https://www.arduino.cc/en/Reference/AttachInterrupt this link] for more details on Arduino UNO external interrupt.
 

=API Details=
Here we will discuss some of the most frequently used APIs related to tasks.

<b>xTaskCreate()</b>: 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 [http://www.freertos.org/a00125.html this link] for more details.<br>

<b>vTaskDelay()</b>: 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 [http://www.freertos.org/a00127.html this link] for more details.<br>

<b>vTaskDelete():</b>This function is used to delete as task. We need to pass the taskHandle of the task to be deleted.<br>
To delete the own task we should pass NULL as the parameter. Please check [http://www.freertos.org/a00126.html this link] for more details. <br>

<b>vTaskSuspend():</b> This function is used to Suspend a task, the suspended remains in the same state util it is resumed.<br>
For this, we need to pass the handle of the tasks that needs to be suspended. Passing NULL will suspend own task. Check [http://www.freertos.org/a00130.html this link] for more details.

<b>vTaskResume():</b> This function is used to resume a suspended task. If the Resumed task has higher priority than the running task then it will preempt the running task or else stays in ready state<br>
For this, we need to pass the handle of the task to be resumed. Check [http://www.freertos.org/a00131.html this link] for more details.

<b>xTaskResumeFromISR():</b> This function is used to resume a task from ISR.<br>
For this, we need to pass the handle of the task to be resumed. Check [http://www.freertos.org/taskresumefromisr.html this link] for more details.<br><br>

=Example1=
<html><script src="https://gist.github.com/SaheblalBagwan/2cf7a0ec1f6924484722ec15409d6e4b.js"></script></html>

=Output1=
[[FILE:ResumingTaskFromISR.png]]
<br>
0. Serial port is initialised Task3 is created with priority 3.
#Task3 starts executing as it has higher priority. NowTask3 creates Task2 and Task4 with priorities 2 and 4. Since Task4 has higher priority compared to Task3, Task4 starts running preempting Task3
#Now Task4 Suspends Task2,Task3 and itself. Now Task2, Task3 and Task4 are in suspended state and will not run until they are resumed.
#Now IDLE tasks keeps running till one of the Task comes out or suspended state. In the current example, only INTO ISR can resume the tasks.
#Once the INT0 interrupt is generated, it will resume Task2.
#Task2 will run for some time and deletes itself.
#Again IDLE task keeps running till interrupt is generated and tasks are resumed.
#Once the INT0 interrupt is generated, it will resume Task3.
#Task3 will run for some time and deletes itself.
#Again IDLE task keeps running till interrupt is generated and tasks are resumed.
#Once the INT0 interrupt is generated, it will resume Task3.
#Task3 will run for some time and deletes itself.
#Only IDLE task is left and it keeps running.