wai_sem
ER wai_sem (ID semid);
This service call acquires a resource from the semaphore specified by parameter semid (subtracts 0x1 from the semaphore counter).
If no resources are acquired from the target semaphore when this service call is issued (no available resources exist), this service call does not acquire resources but queues the invoking task to the target semaphore wait queue and moves it from the RUNNING state to the WAITING state (resource acquisition wait state).
The WAITING state for a semaphore resource is cancelled in the following cases, and then moved to the READY state.
Note Invoking tasks are queued to the target semaphore wait queue in the order defined during configuration (FIFO order or priority order).