Does wiringPiISR() set up Synchronous or Asynchronous edge detection and are inputs e.g. pinMode( , INPUT) set up with hysteresis (Schmitt trigger)? All of these seem options in the Pi GPIO registers but I can't find any documentation or find it in the WiringPi code.
wiringPi uses the Linux sysfs interface to the GPIO for interrupts. I.e. it will not select synchronous or asynchronous, it will use whatever Linux does.
I don't know what Linux does.
I do not think wiringPi touches the hysteresis setting so it will be whatever was previously set (the default at power up in on).
I wrote a program to print out the GPIO registers - it shows the pi linux default is to use synchronous edge detection.
Using wiringPiISR(, INT_EDGE_FALLING,) sets bits in GPFEN0 and wiringPiISR(, INT_EDGE_RISING,) sets bits in GPREN0, wiringPiISR(, INT_EDGE_BOTH,) sets bits in both GPFEN0 and GPREN0. For asynchronous edge detection GPAREN0 and GPAFEN0 would have been used.
Input Hysteresis is controlled by the HYST bit in the GPIO PADS registers - wiringPi sets HYST on (and sets slew rate not limited) as a by product of calling setPadDrive(,) - I suspect it is on already.