Any received message is unpacked appropriately and the contents returned to the calling routine. Only those arguments relevant to the particular message type will be returned.
Note that the received message may be a TIMEOUT message as a result of the timer being set.
If 'timeout' is not MESSYS__INFINITE, it then sets the timer clock going so that we get a timeout if there is no response within timeout milliseconds. The ATIMER package is used to handle timers.
The function then looks for a message on either the external interrupt queue, the transaction acknowledge queue or the timeout queue.
AMS The Unix ADAM Message System