Added compatibility defines for core's variant files

The variant's file compliance is now determined using a define named

ARDUINO_SAMD_VARIANT_COMPLIANCE

that refer to the minimum core version required for this variant file
to work.

Author: cmaglie

cores/arduino/wiring_analog.c

@@ -224,8 +224,17 @@ void analogWrite( uint32_t ulPin, uint32_t ulValue )
   if ( (attr & PIN_ATTR_PWM) == PIN_ATTR_PWM )
   {
     if (attr & PIN_ATTR_TIMER) {
-      pinPeripheral(ulPin, PIO_TIMER);
-    } else { // attr should have PIN_ATTR_TIMER_ALT bit set...
+      #if !(ARDUINO_SAMD_VARIANT_COMPLIANCE >= 10603)
+      // Compatibility for cores based on SAMD core <=1.6.2
+      if (g_APinDescription[ulPin].ulPinType == PIO_TIMER_ALT) {
+        pinPeripheral(ulPin, PIO_TIMER_ALT);
+      } else
+      #endif
+      {
+        pinPeripheral(ulPin, PIO_TIMER);
+      }
+    } else {
+      // We suppose that attr has PIN_ATTR_TIMER_ALT bit set...
       pinPeripheral(ulPin, PIO_TIMER_ALT);
     }
 

variants/arduino_zero/variant.h

@@ -19,6 +19,9 @@
 #ifndef _VARIANT_ARDUINO_ZERO_
 #define _VARIANT_ARDUINO_ZERO_
 
+// The definitions here needs a SAMD core >=1.6.3
+#define ARDUINO_SAMD_VARIANT_COMPLIANCE 10603
+
 /*----------------------------------------------------------------------------
  *        Definitions
  *----------------------------------------------------------------------------*/