Additional lock calls exist in the system that are not available to MFS programmers. These are calls that the system uses to initialize and reset itself; as a result, these calls are passed only via direct calls at system initialization and reset time.
System lock calls are:
LOCK.SEMAPHORE
UNLOCK.SEMAPHORE
SET.USER.SEMAPHORE
An MFS will never receive these calls, and should therefore simply execute a RETURN for the CODE values of 23, 24, and 25.
