In order not to stress the pin you have to avoid voltages (on any pin) exceeding supply voltage. The chance is there that you already "burned" your input pin with the signal generator.
I am not quite familar with GPIO interrupts, but there micht be the chance that you have to reset the interrupt cause.
thanks for reply.
what do you mean by reset the interrupt cause and how can I reset it.
P12.3 is not GPIO but it is SIO pin.