Difference between revisions of "Task Suspend and Resume"

Line 34: Line 34:
 
0. Serial port is initialised and Task1 and Task3 are created with priority 1&3.
 
0. Serial port is initialised and Task1 and Task3 are created with priority 1&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
 
#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,Task4 are in suspended state and will not run until they are resumed.
+
#Now Task4 Suspends Task2,Task3 and itself. Now Task2,Task3 and Task4 are in suspended state and will not run until they are resumed.
 
#At this point Task1 and IDLE are available for the scheduler, So Task1 starts running. It resumes Task2 and immediately Task2 starts running as it has higher priority compared Task1.  
 
#At this point Task1 and IDLE are available for the scheduler, So Task1 starts running. It resumes Task2 and immediately Task2 starts running as it has higher priority compared Task1.  
 
#Task2 will run for some time and deletes itself.
 
#Task2 will run for some time and deletes itself.

Revision as of 17:09, 28 June 2016

In earlier tutorials, we saw how to create and use and delete the tasks.
In this tutorial, we will see how to Suspend and Resume the tasks.


API Details

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

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.

vTaskDelay(): 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.

vTaskDelete():This function is used to delete as task. We need to pass the taskHandle of the task to be deleted.
To delete the own task we should pass NULL as the parameter. Please check this link for more details.

vTaskPrioritySet(): This function is used to change/Set the priority of a task.
For this we need to pass the handle of the task and new priority to vTaskPrioritySet() function. Check this link for more details.

vTaskPriorityGet(): This function is used to get the priority of a task.
For this, we need to pass the handle of the task and it will return the task. Check this link for more details.

vTaskSuspend(): This function is used to Suspend a task, the suspended remains in the same state util it is resumed.
For this, we need to pass the handle of the tasks that needs to be suspended. Passing NULL will suspend own task. Check this link for more details.

vTaskResume(): 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
For this, we need to pass the handle of the task to be resumed. Check this link for more details.

Example1

/***************************************************************************************************
ExploreEmbedded Copyright Notice
****************************************************************************************************
* File: 07-TaskSuspendAndResume
* Version: 15.0
* Author: ExploreEmbedded
* Website: http://www.exploreembedded.com/wiki
* Description: File contains the free rtos example to demonstarte task Suspend and Resume.
This code has been developed and tested on ExploreEmbedded boards.
We strongly believe that the library works on any of development boards for respective controllers.
Check this link http://www.exploreembedded.com/wiki for awesome tutorials on 8051,PIC,AVR,ARM,Robotics,RTOS,IOT.
ExploreEmbedded invests substantial time and effort developing open source HW and SW tools, to support consider
buying the ExploreEmbedded boards.
The ExploreEmbedded libraries and examples are licensed under the terms of the new-bsd license(two-clause bsd license).
See also: http://www.opensource.org/licenses/bsd-license.php
EXPLOREEMBEDDED DISCLAIMS ANY KIND OF HARDWARE FAILURE RESULTING OUT OF USAGE OF LIBRARIES, DIRECTLY OR
INDIRECTLY. FILES MAY BE SUBJECT TO CHANGE WITHOUT PRIOR NOTICE. THE REVISION HISTORY CONTAINS THE INFORMATION
RELATED TO UPDATES.
Permission to use, copy, modify, and distribute this software and its documentation for any purpose
and without fee is hereby granted, provided that this copyright notices appear in all copies
and that both those copyright notices and this permission notice appear in supporting documentation.
**************************************************************************************************/
#include <Arduino_FreeRTOS.h>
TaskHandle_t TaskHandle_1;
TaskHandle_t TaskHandle_2;
TaskHandle_t TaskHandle_3;
TaskHandle_t TaskHandle_4;
void setup()
{
Serial.begin(9600);
Serial.println(F("In Setup function"));
/* Create 4-tasks with priorities 1-4. Capture the Task details to respective handlers */
xTaskCreate(MyTask1, "Task1", 100, NULL, 1, &TaskHandle_1);
xTaskCreate(MyTask2, "Task2", 100, NULL, 2, &TaskHandle_2);
xTaskCreate(MyTask3, "Task3", 100, NULL, 3, &TaskHandle_3);
xTaskCreate(MyTask4, "Task4", 100, NULL, 4, &TaskHandle_4);
}
void loop()
{ // Hooked to Idle Task, will run when CPU is Idle
Serial.println(F("Loop function"));
delay(50);
}
/* Task1 with priority 1 */
static void MyTask1(void* pvParameters)
{
Serial.println(F("Task1 Resuming Task2"));
vTaskResume(TaskHandle_2);
Serial.println(F("Task1 Resuming Task3"));
vTaskResume(TaskHandle_3);
Serial.println(F("Task1 Resuming Task4"));
vTaskResume(TaskHandle_4);
Serial.println(F("Task1 Deleting Itself"));
vTaskDelete(TaskHandle_1);
}
/* Task2 with priority 2 */
static void MyTask2(void* pvParameters)
{
Serial.println(F("Task2, Deleting itself"));
vTaskDelete(NULL); //Delete own task by passing NULL(TaskHandle_2 can also be used)
}
/* Task3 with priority 3 */
static void MyTask3(void* pvParameters)
{
Serial.println(F("Task3, Deleting Itself"));
vTaskDelete(NULL); //Delete own task by passing NULL(TaskHandle_3 can also be used)
}
/* Task4 with priority 4 */
static void MyTask4(void* pvParameters)
{
Serial.println(F("Task4 Running, Suspending all tasks"));
vTaskSuspend(TaskHandle_2); //Suspend Task2/3
vTaskSuspend(TaskHandle_3);
vTaskSuspend(NULL); //Suspend Own Task
Serial.println(F("Back in Task4, Deleting Itself"));
vTaskDelete(TaskHandle_4);
}
view raw 07-TaskSuspendAndResume.c hosted with ❤ by GitHub

Output1

TaskSuspendAndResume.png
0. Serial port is initialised and Task1 and Task3 are created with priority 1&3.

  1. 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
  2. Now Task4 Suspends Task2,Task3 and itself. Now Task2,Task3 and Task4 are in suspended state and will not run until they are resumed.
  3. At this point Task1 and IDLE are available for the scheduler, So Task1 starts running. It resumes Task2 and immediately Task2 starts running as it has higher priority compared Task1.
  4. Task2 will run for some time and deletes itself.
  5. Again we are left with Task1 and IDLE, So Task1 starts running. It resumes Task3 and immediately Task3 starts running as it has higher priority compared to Task1.
  6. Task3 runs for some time and deletes itself.
  7. Again we are left with Task1 and IDLE, So Task1 starts running. It resumes Task4 and immediately Task4 starts running as it has higher priority compared to Task1.
  8. Task4 runs for some time and deletes itself.
  9. Now we are left with Task1 and Idle, so Task1 completes it job and deletes itself.
  10. Finally we are left with IDLE task which continues to run.

Example2

/***************************************************************************************************
ExploreEmbedded Copyright Notice
****************************************************************************************************
* File: 08-TaskSuspendAndResume
* Version: 15.0
* Author: ExploreEmbedded
* Website: http://www.exploreembedded.com/wiki
* Description: File contains the free rtos example to demonstarte task Suspend and Resume.
This code has been developed and tested on ExploreEmbedded boards.
We strongly believe that the library works on any of development boards for respective controllers.
Check this link http://www.exploreembedded.com/wiki for awesome tutorials on 8051,PIC,AVR,ARM,Robotics,RTOS,IOT.
ExploreEmbedded invests substantial time and effort developing open source HW and SW tools, to support consider
buying the ExploreEmbedded boards.
The ExploreEmbedded libraries and examples are licensed under the terms of the new-bsd license(two-clause bsd license).
See also: http://www.opensource.org/licenses/bsd-license.php
EXPLOREEMBEDDED DISCLAIMS ANY KIND OF HARDWARE FAILURE RESULTING OUT OF USAGE OF LIBRARIES, DIRECTLY OR
INDIRECTLY. FILES MAY BE SUBJECT TO CHANGE WITHOUT PRIOR NOTICE. THE REVISION HISTORY CONTAINS THE INFORMATION
RELATED TO UPDATES.
Permission to use, copy, modify, and distribute this software and its documentation for any purpose
and without fee is hereby granted, provided that this copyright notices appear in all copies
and that both those copyright notices and this permission notice appear in supporting documentation.
**************************************************************************************************/
#include <Arduino_FreeRTOS.h>
TaskHandle_t TaskHandle_1;
TaskHandle_t TaskHandle_2;
TaskHandle_t TaskHandle_3;
TaskHandle_t TaskHandle_4;
void setup()
{
Serial.begin(9600);
Serial.println(F("In Setup function"));
/* Create 4-tasks with priorities 1-4. Capture the Task details to respective handlers */
xTaskCreate(MyTask1, "Task1", 100, NULL, 1, &TaskHandle_1);
xTaskCreate(MyTask2, "Task2", 100, NULL, 2, &TaskHandle_2);
xTaskCreate(MyTask3, "Task3", 100, NULL, 3, &TaskHandle_3);
xTaskCreate(MyTask4, "Task4", 100, NULL, 4, &TaskHandle_4);
}
void loop()
{ // Hooked to Idle Task, will run when CPU is Idle
Serial.println(F("Loop function"));
delay(50);
}
/* Task1 with priority 1 */
static void MyTask1(void* pvParameters)
{
Serial.println("Task1 Changing its priority to 5");
vTaskPrioritySet(TaskHandle_1,5); //Now task1 is of highest priority
Serial.println("Task1 Resuming Task2");
vTaskResume(TaskHandle_2);
Serial.println("Task1 Resuming Task3");
vTaskResume(TaskHandle_3);
Serial.println("Task1 Resuming Task4");
vTaskResume(TaskHandle_4);
Serial.println("Task1 Deleting Itself");
vTaskDelete(TaskHandle_1);
}
/* Task2 with priority 2 */
static void MyTask2(void* pvParameters)
{
Serial.println(F("Task2, Deleting itself"));
vTaskDelete(NULL); //Delete own task by passing NULL(TaskHandle_2 can also be used)
}
/* Task3 with priority 3 */
static void MyTask3(void* pvParameters)
{
Serial.println(F("Task3, Deleting Itself"));
vTaskDelete(NULL); //Delete own task by passing NULL(TaskHandle_3 can also be used)
}
/* Task4 with priority 4 */
static void MyTask4(void* pvParameters)
{
Serial.println(F("Task4 Running, Suspending all tasks"));
vTaskSuspend(TaskHandle_2); //Suspend Task2/3
vTaskSuspend(TaskHandle_3);
vTaskSuspend(NULL); //Suspend Own Task
Serial.println(F("Back in Task4, Deleting Itself"));
vTaskDelete(TaskHandle_4);
}
view raw 08-TaskSuspendAndResume.c hosted with ❤ by GitHub

Output2

TaskSuspendAndResume2.png
0. Serial port is initialised and Task1 and Task3 are created with priority 1&3.

  1. 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
  2. Now Task4 Suspends Task2,Task3 and itself. Now Task2,Task3,Task4 are in suspended state and will not run until they are resumed.
  3. At this point Task1 and IDLE are available for the scheduler, So Task1 starts running. It resumes Task2 and immediately Task2 starts running as it has higher priority compared Task1.
Retrieved from "https://exploreembedded.com/wiki/index.php?title=Task_Suspend_and_Resume&oldid=9459"