Add I2C Repeated Start Capability

Adjust requestFrom, endTransmission, and startTransmissionWire to handle
repeated starts

Author: legomanww

cores/arduino/SERCOM.cpp

@@ -476,12 +476,17 @@ void SERCOM::prepareCommandBitsWire(SercomMasterCommandWire cmd)
 }
 
 bool SERCOM::startTransmissionWIRE(uint8_t address, SercomWireReadWriteFlag flag)
+{
+	return startTransmissionWIRE(address, flag, false);
+}
+
+bool SERCOM::startTransmissionWIRE(uint8_t address, SercomWireReadWriteFlag flag, bool repeatedStart)
 {
   // 7-bits address + 1-bits R/W
   address = (address << 0x1ul) | flag;
 
   // Wait idle bus mode
-  while ( !isBusIdleWIRE() );
+  while ( !repeatedStart && !isBusIdleWIRE());
 
   // Send start and address
   sercom->I2CM.ADDR.bit.ADDR = address;

cores/arduino/SERCOM.h

@@ -194,6 +194,7 @@ class SERCOM
     void prepareAckBitWIRE( void ) ;
     void prepareCommandBitsWire(SercomMasterCommandWire cmd);
 		bool startTransmissionWIRE(uint8_t address, SercomWireReadWriteFlag flag) ;
+		bool startTransmissionWIRE(uint8_t address, SercomWireReadWriteFlag flag, bool repeatedStart) ;
 		bool sendDataMasterWIRE(uint8_t data) ;
 		bool sendDataSlaveWIRE(uint8_t data) ;
 		bool isMasterWIRE( void ) ;

libraries/Wire/Wire.cpp

@@ -68,7 +68,7 @@ uint8_t TwoWire::requestFrom(uint8_t address, size_t quantity, bool stopBit)
 
   size_t byteRead = 0;
 
-  if(sercom->startTransmissionWIRE(address, WIRE_READ_FLAG))
+  if(sercom->startTransmissionWIRE(address, WIRE_READ_FLAG, repeatedStart))
   {
     // Read first data
     rxBuffer.store_char(sercom->readDataWIRE());
@@ -82,7 +82,12 @@ 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
-    sercom->prepareCommandBitsWire(WIRE_MASTER_ACT_STOP);   // Send Stop
+	
+	repeatedStart = !stopBit;
+	if (stopBit)
+	{
+		sercom->prepareCommandBitsWire(WIRE_MASTER_ACT_STOP);   // Send Stop
+	}
   }
 
   return byteRead;
@@ -112,7 +117,7 @@ uint8_t TwoWire::endTransmission(bool stopBit)
   transmissionBegun = false ;
 
   // Start I2C transmission
-  if ( !sercom->startTransmissionWIRE( txAddress, WIRE_WRITE_FLAG ) )
+  if ( !sercom->startTransmissionWIRE( txAddress, WIRE_WRITE_FLAG, repeatedStart ) )
   {
     sercom->prepareCommandBitsWire(WIRE_MASTER_ACT_STOP);
     return 2 ;  // Address error
@@ -128,7 +133,12 @@ uint8_t TwoWire::endTransmission(bool stopBit)
       return 3 ;  // Nack or error
     }
   }
-  sercom->prepareCommandBitsWire(WIRE_MASTER_ACT_STOP);
+  
+  repeatedStart = !stopBit;
+  if (stopBit)
+  {
+	  sercom->prepareCommandBitsWire(WIRE_MASTER_ACT_STOP);
+  }   
 
   return 0;
 }

libraries/Wire/Wire.h

@@ -67,7 +67,8 @@ class TwoWire : public Stream
     uint8_t _uc_pinSCL;
 
     bool transmissionBegun;
-
+	bool repeatedStart;
+	
     // RX Buffer
     RingBuffer rxBuffer;