[Alan Anderson]

To fix your code, you also need to make sure that you only process the change once each time the switch is activated.

  last_trig = 0;
  ...
  if (p3_sw_trig ==1 && last_trig == 0 && pnu == 0)
  {
    ...
    pnu += 1;
  }
  if (p3_sw_trig == 1 && last_trig == 0 && pnu == 1)
  {
    ...
    pnu = 0;
  }
  last_trig = p3_sw_trig;