1. This function creates or updates an interval timer: after a timer has been armed by a call to this routine an event of class EVENT_TIMER is scheduled for being sent to the model after the specified amount of time has elapsed. The value of such an event is the timer identifier tid. Note that the system will not emit a new event if an identical event is already in the queue.

2. If the option rep is set to false the timer is released after its termination, otherwise it is immediately re-armed with the same interval after each expiration until it is explicitly cancelled (see canceltimer).

3. If the provided identifier tid is not positive a new timer is created with a newly generated identifier, this corresponds to the behaviour of the second form of this function.

4. When the provided identifier corresponds to an existing timer, this one is first cancelled with a call to canceltimer before being re-created with the new properties.