Used by the routine at 6EC5. Returns with the interval in A, which indicates the minimum number of subintervals of 0.64s that the current message should be displayed for.
|Collect the urgent message number from 75C9
|Is it 0 (no message)?
|Jump if so
|Collect the index of the current message in the queue from 7FB7
|A=index of the next message in the queue
|Point HL at the slot for the next message in the queue
|There are up to 7 messages ahead in the queue
|A=urgent message number
|Set the zero flag if the urgent message is in this slot in the queue
|Move HL along to the next slot in the message queue (or past the end of the queue and into the bullet buffers at 7FC0 and 7FC4, which is a bug)
|Jump unless the urgent message is at this position in the queue
|Set A=1 so that the next message is displayed as soon as possible
|Jump back until all messages in the queue have been checked
|Clear the urgent message number at 75C9: it was not in the queue
|Collect the normal message display interval from 6FC4