OK, I see what you meant. This is quite easy to deal with really: Check the timer for an overflow or an out-of-bound value (in case the third edge arrives before the overflow).

However, the way I would tackle this specific case is to feed the preconditioned signal into a T flip-flop and connect it's output to /INT0 (or /INT1) and use Timer0 (1) in gated mode. This will give you a direct measurement of the length of a full period, with no hassle and time enough to do the maths.


Rob.