Hi @ruchiatavr
Is the function:
C[cornerNo]->sync();
...waiting to synchronise with some external event?
If it's the case, then it's better to use one FreeRTOS task synchronisation methods, such as task notification or binary semaphores.
Hardware interrupts (as well as PCINT interrupts) are handled outside the context of FreeRTOS operating system, however it's possible to use the FreeRTOS interrupt safe "FromISR" API functions from within the interrrupt, to synchronise or pass information from the interrupt into a FreeRTOS task.