Refactor digitalPinToInterrupt macro

This way the behaviour matches SAMD core (both attachInterrupt(pin)
and attachInterrupt(digitalPinToInterrupt(pin) can be used.

Fixes #18

Author: facchinm

cores/arduino/Arduino.h

@@ -125,7 +125,7 @@ bool isDoubleBondedActive(uint8_t pin);
 #define portToPortStruct(port) ( (port < NUM_TOTAL_PORTS) ? ((PORT_t *)&PORTA + port) : NULL)
 #define digitalPinToPortStruct(pin) ( (pin < NUM_TOTAL_PINS) ? ((PORT_t *)&PORTA + digitalPinToPort(pin)) : NULL)
 #define getPINnCTRLregister(port, bit_pos) ( ((port != NULL) && (bit_pos < NOT_A_PIN)) ? ((volatile uint8_t *)&(port->PIN0CTRL) + bit_pos) : NULL )
-#define digitalPinToInterrupt(p) ( digitalPinToPort(p) * 8 + digitalPinToBitPosition(p) )
+#define digitalPinToInterrupt(P) (P)
 
 #define portOutputRegister(P) ( (volatile uint8_t *)( &portToPortStruct(P)->OUT ) )
 #define portInputRegister(P) ( (volatile uint8_t *)( &portToPortStruct(P)->IN ) )

cores/arduino/WInterrupts.c

@@ -41,7 +41,7 @@ void attachInterrupt(uint8_t pin, void (*userFunc)(void), PinStatus mode) {
   if(bit_pos == NOT_A_PIN) return;
 
   /* Get interrupt number from pin */
-  uint8_t interruptNum = digitalPinToInterrupt(pin);
+  uint8_t interruptNum = (digitalPinToPort(pin) * 8) + bit_pos;
 
   /* Check interrupt number and apply function pointer to correct array index */
   if(interruptNum < EXTERNAL_NUM_INTERRUPTS) {
@@ -90,7 +90,7 @@ void detachInterrupt(uint8_t pin) {
   if(bit_pos == NOT_A_PIN) return;
 
   /* Get interrupt number from pin */
-  uint8_t interruptNum = digitalPinToInterrupt(pin);
+  uint8_t interruptNum = (digitalPinToPort(pin) * 8) + bit_pos;
 
   if(interruptNum < EXTERNAL_NUM_INTERRUPTS) {
     // Disable the interrupt.