Bugfixes with the protocol.

- Bitmasks need to be equal, not just result in non-zero
 - Only read status once in case it changes under us
 - Logical and not binary and when checking for acks on sending
 - We need to stop the bus when receiving the last byte
 - Force the bus into idle mode when we are Initing

LUFA/Drivers/Peripheral/XMEGA/TWI_XMEGA.c

@@ -34,6 +34,10 @@
 #define  __INCLUDE_FROM_TWI_C
 #include "../TWI.h"
 
+static inline bool bitmask_is_set(uint8_t byte, uint8_t mask) {
+  return (byte & mask) == mask;
+}
+
 uint8_t TWI_StartTransmission(TWI_t *twi,
                               const uint8_t SlaveAddress,
                               const uint8_t TimeoutMS)
@@ -45,22 +49,25 @@ uint8_t TWI_StartTransmission(TWI_t *twi,
   TimeoutRemaining = (TimeoutMS * 100);
   while (TimeoutRemaining)
   {
-    if (twi->MASTER.STATUS & (TWI_MASTER_WIF_bm | TWI_MASTER_ARBLOST_bm)) 
+    uint8_t status = twi->MASTER.STATUS;
+    if (bitmask_is_set(status, TWI_MASTER_WIF_bm | TWI_MASTER_ARBLOST_bm))
     {
       // Case 1: Arbitration lost.  Try again. (or error)
       twi->MASTER.ADDR = SlaveAddress;
     }
-    else if (twi->MASTER.STATUS & (TWI_MASTER_WIF_bm | TWI_MASTER_RXACK_bm))
+    else if (bitmask_is_set(status, TWI_MASTER_WIF_bm | TWI_MASTER_RXACK_bm))
     {
       // Case 2: No response from slave.
+      // We need to release the bus.
+      TWI_StopTransmission(twi);
       return TWI_ERROR_SlaveResponseTimeout;
     }
-    else if (twi->MASTER.STATUS & (TWI_MASTER_WIF_bm))
+    else if (status & TWI_MASTER_WIF_bm)
     {
       // Case 3: Slave ACK the Write. Ready!
       return TWI_ERROR_NoError;
     }
-    else if (twi->MASTER.STATUS & (TWI_MASTER_RIF_bm))
+    else if (status & TWI_MASTER_RIF_bm)
     {
       // Case 4: Slave ACK the Read. Ready! (a byte will be read)
       return TWI_ERROR_NoError;
@@ -73,7 +80,7 @@ uint8_t TWI_StartTransmission(TWI_t *twi,
   if (!(TimeoutRemaining)) {
     if (twi->MASTER.STATUS & TWI_MASTER_CLKHOLD_bm) {
       // Release the bus if we're holding it.
-      twi->MASTER.CTRLC = TWI_MASTER_CMD_STOP_gc;
+      TWI_StopTransmission(twi);
     }
   }
   return TWI_ERROR_BusCaptureTimeout;
@@ -84,20 +91,20 @@ bool TWI_SendByte(TWI_t *twi, const uint8_t Byte)
   // We assume we're ready to write!
   twi->MASTER.DATA = Byte;
   while (!(twi->MASTER.STATUS & TWI_MASTER_WIF_bm));
-  return (twi->MASTER.STATUS & TWI_MASTER_WIF_bm) & !(twi->MASTER.STATUS & TWI_MASTER_RXACK_bm);
+  return (twi->MASTER.STATUS & TWI_MASTER_WIF_bm) && !(twi->MASTER.STATUS & TWI_MASTER_RXACK_bm);
 }
 
 bool TWI_ReceiveByte(TWI_t *twi, uint8_t* const Byte,
 					 const bool LastByte)
 {
   // If we're here, we should already be reading.  Wait if we haven't read yet.
-  if (twi->MASTER.STATUS & (TWI_MASTER_BUSERR_bm | TWI_MASTER_ARBLOST_bm)) {
+  if (bitmask_is_set(twi->MASTER.STATUS, TWI_MASTER_BUSERR_bm | TWI_MASTER_ARBLOST_bm)) {
     return false;
   }
   while (!(twi->MASTER.STATUS & TWI_MASTER_RIF_bm));
   *Byte = twi->MASTER.DATA;
   if (LastByte)
-    twi->MASTER.CTRLC = TWI_MASTER_ACKACT_bm | TWI_MASTER_CMD_RECVTRANS_gc;
+    twi->MASTER.CTRLC = TWI_MASTER_ACKACT_bm | TWI_MASTER_CMD_STOP_gc;
   else
     twi->MASTER.CTRLC = TWI_MASTER_CMD_RECVTRANS_gc;
   return true;
@@ -137,8 +144,8 @@ uint8_t TWI_ReadPacket(TWI_t *twi,
 				}
 			}
 
-			TWI_StopTransmission(twi);
 		}
+    TWI_StopTransmission(twi);
 	}
 
 	return ErrorCode;
@@ -153,7 +160,6 @@ uint8_t TWI_WritePacket(TWI_t *twi,
                         uint8_t Length)
 {
 	uint8_t ErrorCode;
-
 	if ((ErrorCode = TWI_StartTransmission(twi, (SlaveAddress & TWI_DEVICE_ADDRESS_MASK) | TWI_ADDRESS_WRITE,
 	                                       TimeoutMS)) == TWI_ERROR_NoError)
 	{

LUFA/Drivers/Peripheral/XMEGA/TWI_XMEGA.h

@@ -184,8 +184,11 @@
 			static inline void TWI_Init(TWI_t *twi, const uint8_t Baud) ATTR_ALWAYS_INLINE ATTR_NON_NULL_PTR_ARG(1);
 			static inline void TWI_Init(TWI_t *twi, const uint8_t Baud)
 			{
+        twi->CTRL = 0x00;
         twi->MASTER.BAUD = Baud;
-        twi->MASTER.CTRLA |= TWI_MASTER_ENABLE_bm;
+        twi->MASTER.CTRLA = TWI_MASTER_ENABLE_bm;
+        twi->MASTER.CTRLB = 0;
+        twi->MASTER.STATUS = TWI_MASTER_BUSSTATE_IDLE_gc;
 			}
 
 			/** Turns off the TWI driver hardware. If this is called, any further TWI operations will require a call to
@@ -206,7 +209,7 @@
 			static inline void TWI_StopTransmission(TWI_t *twi) ATTR_ALWAYS_INLINE ATTR_NON_NULL_PTR_ARG(1);
 			static inline void TWI_StopTransmission(TWI_t *twi)
 			{
-        twi->MASTER.CTRLC = TWI_MASTER_CMD_STOP_gc;
+        twi->MASTER.CTRLC = TWI_MASTER_ACKACT_bm | TWI_MASTER_CMD_STOP_gc;
 			}
 
 		/* Function Prototypes: */