Add check for arbitration in I2C master read

Add check for errors during I2C master read (likely loss of arbitration) so that the operation can be aborted and code does not get stuck in an infinite loop

Author: Alberto Mannari

cores/arduino/SERCOM.cpp

@@ -638,7 +638,7 @@ uint8_t SERCOM::readDataWIRE( void )
 {
   if(isMasterWIRE())
   {
-    while( sercom->I2CM.INTFLAG.bit.SB == 0 )
+    while( sercom->I2CM.INTFLAG.bit.SB == 0 && sercom->I2CM.INTFLAG.bit.MB == 0 )
     {
       // Waiting complete receive
     }

libraries/Wire/Wire.cpp

@@ -78,8 +78,9 @@ uint8_t TwoWire::requestFrom(uint8_t address, size_t quantity, bool stopBit)
     // Read first data
     rxBuffer.store_char(sercom->readDataWIRE());
 
+    bool busOwner;
     // Connected to slave
-    for (byteRead = 1; byteRead < quantity; ++byteRead)
+    for (byteRead = 1; byteRead < quantity && (busOwner = sercom->isBusOwnerWIRE()); ++byteRead)
     {
       sercom->prepareAckBitWIRE();                          // Prepare Acknowledge
       sercom->prepareCommandBitsWire(WIRE_MASTER_ACT_READ); // Prepare the ACK command for the slave
@@ -88,9 +89,14 @@ uint8_t TwoWire::requestFrom(uint8_t address, size_t quantity, bool stopBit)
     sercom->prepareNackBitWIRE();                           // Prepare NACK to stop slave transmission
     //sercom->readDataWIRE();                               // Clear data register to send NACK
 
-    if (stopBit)
+    if (stopBit && busOwner)
     {
-      sercom->prepareCommandBitsWire(WIRE_MASTER_ACT_STOP);   // Send Stop
+      sercom->prepareCommandBitsWire(WIRE_MASTER_ACT_STOP);   // Send Stop unless arbitration was lost
+    }
+
+    if (!busOwner)
+    {
+      byteRead--;   // because last read byte was garbage/invalid
     }
   }