deadlock detect and early return in startTransmissionWIRE

Author: asserta6

cores/arduino/SERCOM.cpp

@@ -499,6 +499,19 @@ bool SERCOM::startTransmissionWIRE(uint8_t address, SercomWireReadWriteFlag flag
   // 7-bits address + 1-bits R/W
   address = (address << 0x1ul) | flag;
 
+  // If another master owns the bus or the last bus owner has not properly
+  // sent a stop, return failure early. This will prevent some misbehaved
+  // devices from deadlocking here at the cost of the caller being responsible
+  // for retrying the failed transmission. See SercomWireBusState for the
+  // possible bus states.
+  if(!isBusOwnerWIRE())
+  {
+    if( isBusBusyWIRE() || (isArbLostWIRE() && !isBusIdleWIRE()) )
+    {
+      return false;
+    }
+  }
+
   // Wait idle or owner bus mode
   while ( !isBusIdleWIRE() && !isBusOwnerWIRE() );
 
@@ -596,6 +609,16 @@ bool SERCOM::isBusOwnerWIRE( void )
   return sercom->I2CM.STATUS.bit.BUSSTATE == WIRE_OWNER_STATE;
 }
 
+bool SERCOM::isArbLostWIRE( void )
+{
+  return sercom->I2CM.STATUS.bit.ARBLOST == 1;
+}
+
+bool SERCOM::isBusBusyWIRE( void )
+{
+  return sercom->I2CM.STATUS.bit.BUSSTATE == WIRE_BUSY_STATE;
+}
+
 bool SERCOM::isDataReadyWIRE( void )
 {
   return sercom->I2CS.INTFLAG.bit.DRDY;

cores/arduino/SERCOM.h

@@ -202,6 +202,8 @@ class SERCOM
 		bool isSlaveWIRE( void ) ;
 		bool isBusIdleWIRE( void ) ;
 		bool isBusOwnerWIRE( void ) ;
+		bool isArbLostWIRE( void );
+		bool isBusBusyWIRE( void );
 		bool isDataReadyWIRE( void ) ;
 		bool isStopDetectedWIRE( void ) ;
 		bool isRestartDetectedWIRE( void ) ;