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KernelinsideTask control

Updated Jul 2025

xTaskResumeFromISR()

[Task Control]

task. h

1BaseType_t xTaskResumeFromISR( TaskHandle_t xTaskToResume );



INCLUDE_vTaskSuspend
and 
INCLUDE_xTaskResumeFromISR
must be defined as 1 for this function to be available. See the RTOS Configuration documentation for more information.

A function to resume a suspended task that can be called from within an ISR.

A task that has been suspended by one of more calls to 

vTaskSuspend()
will be made available for running again by a single call to 
xTaskResumeFromISR()
.

xTaskResumeFromISR()
is generally considered a dangerous function because its actions are not latched. For this reason it should definitely not be used to synchronise a task with an interrupt if there is a chance that the interrupt could arrive prior to the task being suspended, and therefore the interrupt being lost. Use of a semaphore, or preferable a direct to task notification, would avoid this eventuality. A worked example that uses a direct to task notification is provided.

Parameters:

  • xTaskToResume

    Handle to the task being readied.

Returns:

  • pdTRUE if resuming the task should result in a context switch,
  • pdFALSE otherwise. This is used by the ISR to determine if a context switch may be required following the ISR.

Example usage:

1TaskHandle_t xHandle;
2

3void vAFunction( void )
4{
5    // Create a task, storing the handle.
6    xTaskCreate( vTaskCode, "NAME", STACK_SIZE, NULL, tskIDLE_PRIORITY, &xHandle );
7

8    // ... Rest of code.
9}
10

11void vTaskCode( void *pvParameters )
12{
13    // The task being suspended and resumed.
14    for( ;; )
15    {
16        // ... Perform some function here.
17

18        // The task suspends itself.
19        vTaskSuspend( NULL );
20

21        // The task is now suspended, so will not reach here until the ISR resumes it.
22    }
23}
24

25void vAnExampleISR( void )
26{
27    BaseType_t xYieldRequired;
28

29    // Resume the suspended task.
30    xYieldRequired = xTaskResumeFromISR( xHandle );
31

32    // We should switch context so the ISR returns to a different task.
33    // NOTE:  How this is done depends on the port you are using.  Check
34    // the documentation and examples for your port.
35    portYIELD_FROM_ISR( xYieldRequired );
36}