added optional custom handler to Serial interrupt

added optional custom handler to Serial interrupt. Is minor enhancement
of NeoHWSerial by SlashDevin
(https://github.com/SlashDevin/NeoHWSerial), as user function also gets
UART status as parameter to e.g. detect LIN break in user routine.

Added as core extension instead of library due to similar extension for
Due (https://github.com/gicking/ArduinoCore-sam) which AFAIK cannot be
implemented as library.

cores/arduino/HardwareSerial.cpp

@@ -20,6 +20,8 @@
   Modified 28 September 2010 by Mark Sproul
   Modified 14 August 2012 by Alarus
   Modified 3 December 2013 by Matthijs Kooijman
+  Modified 2 November 2015 by SlashDev
+  Modified 7 November 2019 by Georg Icking-Konert
 */
 
 #include <stdlib.h>
@@ -278,4 +280,12 @@ size_t HardwareSerial::write(uint8_t c)
   return 1;
 }
 
+void HardwareSerial::attachInterrupt( isr_t fn )
+{
+  uint8_t oldSREG = SREG;
+  cli();
+  _isr = fn;
+  SREG = oldSREG;
+}
+
 #endif // whole file

cores/arduino/HardwareSerial.h

@@ -19,6 +19,8 @@
   Modified 28 September 2010 by Mark Sproul
   Modified 14 August 2012 by Alarus
   Modified 3 December 2013 by Matthijs Kooijman
+  Modified 2 November 2015 by SlashDev
+  Modified 7 November 2019 by Georg Icking-Konert
 */
 
 #ifndef HardwareSerial_h
@@ -137,6 +139,15 @@ class HardwareSerial : public Stream
     // Interrupt handlers - Not intended to be called externally
     inline void _rx_complete_irq(void);
     void _tx_udr_empty_irq(void);
+
+    typedef void (* isr_t)( uint8_t d=0x00, uint8_t s=0x00 );
+    void attachInterrupt( isr_t fn );
+    void detachInterrupt() { attachInterrupt( (isr_t) NULL ); };
+  private:
+    isr_t  _isr;
+
+    HardwareSerial( const HardwareSerial & );
+    HardwareSerial & operator =( const HardwareSerial &);
 };
 
 #if defined(UBRRH) || defined(UBRR0H)

cores/arduino/HardwareSerial0.cpp

@@ -20,6 +20,8 @@
   Modified 28 September 2010 by Mark Sproul
   Modified 14 August 2012 by Alarus
   Modified 3 December 2013 by Matthijs Kooijman
+  Modified 2 November 2015 by SlashDev
+  Modified 7 November 2019 by Georg Icking-Konert
 */
 
 #include "Arduino.h"

cores/arduino/HardwareSerial1.cpp

@@ -20,6 +20,8 @@
   Modified 28 September 2010 by Mark Sproul
   Modified 14 August 2012 by Alarus
   Modified 3 December 2013 by Matthijs Kooijman
+  Modified 2 November 2015 by SlashDev
+  Modified 7 November 2019 by Georg Icking-Konert
 */
 
 #include "Arduino.h"

cores/arduino/HardwareSerial2.cpp

@@ -20,6 +20,8 @@
   Modified 28 September 2010 by Mark Sproul
   Modified 14 August 2012 by Alarus
   Modified 3 December 2013 by Matthijs Kooijman
+  Modified 2 November 2015 by SlashDev
+  Modified 7 November 2019 by Georg Icking-Konert
 */
 
 #include "Arduino.h"

cores/arduino/HardwareSerial3.cpp

@@ -20,6 +20,8 @@
   Modified 28 September 2010 by Mark Sproul
   Modified 14 August 2012 by Alarus
   Modified 3 December 2013 by Matthijs Kooijman
+  Modified 2 November 2015 by SlashDev
+  Modified 7 November 2019 by Georg Icking-Konert
 */
 
 #include "Arduino.h"

cores/arduino/HardwareSerial_private.h

@@ -19,6 +19,8 @@
   Modified 23 November 2006 by David A. Mellis
   Modified 28 September 2010 by Mark Sproul
   Modified 14 August 2012 by Alarus
+  Modified 2 November 2015 by SlashDev
+  Modified 7 November 2019 by Georg Icking-Konert
 */
 
 #include "wiring_private.h"
@@ -92,32 +94,44 @@ HardwareSerial::HardwareSerial(
     _ucsra(ucsra), _ucsrb(ucsrb), _ucsrc(ucsrc),
     _udr(udr),
     _rx_buffer_head(0), _rx_buffer_tail(0),
-    _tx_buffer_head(0), _tx_buffer_tail(0)
+    _tx_buffer_head(0), _tx_buffer_tail(0),
+    _isr(0)
 {
 }
 
 // Actual interrupt handlers //////////////////////////////////////////////////////////////
 
 void HardwareSerial::_rx_complete_irq(void)
 {
-  if (bit_is_clear(*_ucsra, UPE0)) {
-    // No Parity error, read byte and store it in the buffer if there is
-    // room
-    unsigned char c = *_udr;
-    rx_buffer_index_t i = (unsigned int)(_rx_buffer_head + 1) % SERIAL_RX_BUFFER_SIZE;
+  // user function was attached -> call it with data and status byte 
+  if (_isr) {
+    unsigned char status = *_ucsra;
+    unsigned char data = *_udr;
+    _isr( data, status );
+  }
 
-    // if we should be storing the received character into the location
-    // just before the tail (meaning that the head would advance to the
-    // current location of the tail), we're about to overflow the buffer
-    // and so we don't write the character or advance the head.
-    if (i != _rx_buffer_tail) {
-      _rx_buffer[_rx_buffer_head] = c;
-      _rx_buffer_head = i;
-    }
-  } else {
-    // Parity error, read byte but discard it
-    *_udr;
-  };
+  // default: save data in ring buffer
+  else {  
+    if (bit_is_clear(*_ucsra, UPE0)) {
+      unsigned char c = *_udr;
+      // No Parity error, read byte and store it in the buffer if there is
+      // room
+      rx_buffer_index_t i = (unsigned int)(_rx_buffer_head + 1) % SERIAL_RX_BUFFER_SIZE;
+
+      // if we should be storing the received character into the location
+      // just before the tail (meaning that the head would advance to the
+      // current location of the tail), we're about to overflow the buffer
+      // and so we don't write the character or advance the head.
+      if (i != _rx_buffer_tail) {
+        _rx_buffer[_rx_buffer_head] = c;
+        _rx_buffer_head = i;
+      }
+    } 
+    else {
+      // Parity error, read byte but discard it
+      *_udr;
+    };
+  }
 }
 
 #endif // whole file