Three questions, with a bit of background. Many of the functions that may be safely called from an ISR have a pointer parameter often named pxHigherPriorityTaskWoken. My understanding is that if this is not NULL, and the associated call causes a higher priority task to unblock, then *pxHigherPriorityTaskWoken will be set true, and the calling ISR should call portYIELDFROMISR() prior to returning to activate the unblocked, higher priority task.

1. Is this a correct understanding?
2. If portYIELDFROMISR isn’t called, then the task will eventually be unblocked, but not until some other event causes the scheduler to reevalute the ready tasks; is that correct?

Finally, I’ve noticed that the online API documentation (example: http://www.freertos.org/a00119.html) has changed to add this note to the pxHigherPriorityTaskWoken parameter:

“From FreeRTOS V7.3.0 pxHigherPriorityTaskWoken is an optional parameter and can be set to NULL.” 3. If you don’t supply this parameter, then you won’t be notified of a higher-priority task being woken, so it won’t get scheduled as soon as possible; is that the sole effect of not using this parameter? 4.

1) Yes. 2) Yes, for example, the tick interrupt. 3) Yes, It isn’t quite ‘optional’, as you have to provide something, but if you pass a NULL (or a 0) then you just don’t get the indication that someone has woken. In effect, when/if it is time to set the flag true, that operation is skipped if you pass a null pointer.