So what does using the character definition of a Round give us? Recall a round is usually "a span of time from one round to the same initiative count in the next round".
Character A takes a full round's worth of actions (including a Swift action) on initiative count N. He ends his round.
On Initiative count N-1, the situation changes and the character wants to use an Immediate action outside his turn. He can, but at the sacrifice of his next Immediate action on his next round.
Character A takes a full round's worth of actions (including a Swift action) on initiative count N. He ends his round.
On Initiative count N-1, the situation changes and the character wants to use an Immediate action outside his turn. He can, but at the sacrifice of his next Immediate action on his next round.