Provide irq safe implementation of RingBuffer

Alternative way to fix #580 without restoring the buggy RingBuffer implementation from API

Author: facchinm

cores/arduino/SafeRingBuffer.h

@@ -0,0 +1,56 @@
+/*
+  Copyright (c) 2020 Arduino.  All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+  See the GNU Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+*/
+
+#ifdef __cplusplus
+
+#ifndef _SAFE_RING_BUFFER_
+#define _SAFE_RING_BUFFER_
+
+#include <api/RingBuffer.h>
+#include "sync.h"
+
+namespace arduino {
+
+template <int N>
+class SafeRingBufferN : public RingBufferN<N>
+{
+  public:
+    int read_char();
+    void store_char( uint8_t c ) ;
+};
+
+typedef SafeRingBufferN<SERIAL_BUFFER_SIZE> SafeRingBuffer;
+
+template <int N>
+int SafeRingBufferN<N>::read_char() {
+  synchronized {
+    return RingBufferN<N>::read_char();
+  }
+}
+
+template <int N>
+void SafeRingBufferN<N>::store_char(uint8_t c) {
+  synchronized {
+    RingBufferN<N>::store_char(c);
+  }
+}
+
+}
+
+#endif /* _SAFE_RING_BUFFER_ */
+#endif /* __cplusplus */

cores/arduino/Uart.h

@@ -20,7 +20,7 @@
 
 #include "api/HardwareSerial.h"
 #include "SERCOM.h"
-#include "api/RingBuffer.h"
+#include "SafeRingBuffer.h"
 
 #define SERIAL_BUFFER_SIZE  64
 
@@ -46,8 +46,8 @@ class Uart : public HardwareSerial
 
   private:
     SERCOM *sercom;
-    RingBuffer rxBuffer;
-    RingBuffer txBuffer;
+    SafeRingBuffer rxBuffer;
+    SafeRingBuffer txBuffer;
 
     uint8_t uc_pinRX;
     uint8_t uc_pinTX;