As I recall, the external interrupts are edge triggered, so it would not
matter how long the pin stayed in either state. It sets the IF flag on the
edge, not the level. If your ISR does its work and clears the IF while the
pin is still high, that's fine. Assuming a positive edge tigger, the edge
when the pin goes low is ignored, and the following positive edge is
detected. You mention you have a switch driving the external interrupt
pin. Are you dealing with switch bounce? You could generate a bunch of
interrupts on one switch closure, and again when the switch is released,
due to bounce. You can debounce in hardware prior to the interrupt line,
or, instead, poll the switch using a timer interrupt and require the
switch to be in the same position for some number of calls of the timer
interrupt.

Harold


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