Index: firmware/App/Services/SystemComm.c
===================================================================
diff -u -r070554b23739bf16ea2bf9528ebabda1ce0ffeb3 -rd9cc76524777a12ba77b58ce95416dddfb032997
--- firmware/App/Services/SystemComm.c	(.../SystemComm.c)	(revision 070554b23739bf16ea2bf9528ebabda1ce0ffeb3)
+++ firmware/App/Services/SystemComm.c	(.../SystemComm.c)	(revision d9cc76524777a12ba77b58ce95416dddfb032997)
@@ -68,12 +68,12 @@
 static U08 pcRecvPacket[PC_MESSAGE_PACKET_SIZE] = {0,0,0,0,0,0,0,0};
 
 // DMA control records
-static g_dmaCTRL pcDMAXmitControlRecord;
-static g_dmaCTRL pcDMARecvControlRecord;
+static g_dmaCTRL pcDMAXmitControlRecord;            // DMA transmit control record (UART-debug)
+static g_dmaCTRL pcDMARecvControlRecord;            // DMA receive control record (UART-debug)
 
-static BOOL dgIsCommunicating = FALSE;
-static BOOL uiIsCommunicating = FALSE;
-static BOOL uiDidCommunicate = FALSE;
+static BOOL dgIsCommunicating = FALSE;              // has DG sent a message since last check
+static BOOL uiIsCommunicating = FALSE;              // has UI sent a message since last check
+static BOOL uiDidCommunicate = FALSE;               // has UI every sent a message
 
 // ********** private function prototypes **********
 
@@ -82,8 +82,8 @@
 static BOOL isCANBoxForRecv( CAN_MESSAGE_BOX_T srcCANBox );
 
 static COMM_BUFFER_T findNextHighestPriorityCANPacketToTransmit( void );
-static void transmitNextCANPacket( void );
-static void transmitNextUARTPacket( void );
+static U32 transmitNextCANPacket( void );
+static U32 transmitNextUARTPacket( void );
 
 static void processIncomingData( void );
 static U32 parseMessageFromBuffer( U08 *data, U32 len );
@@ -222,13 +222,23 @@
     // if CAN transmitter is idle, start transmitting any pending packets
     if ( FALSE == isCAN1TransmitInProgress() )
     {
-        transmitNextCANPacket();
+        U32 bytesXmitted = transmitNextCANPacket();
+
+        if ( bytesXmitted > 0 )
+        {
+            signalCANXmitsInitiated();
+        }
     }
 
     // if UART transmitter is idle, start transmitting any pending packets
     if ( FALSE == isSCI1DMATransmitInProgress() )
     {
-        transmitNextUARTPacket();
+        U32 bytesXmitted = transmitNextUARTPacket();
+
+        if ( bytesXmitted > 0 )
+        {
+            signalSCI1XmitsInitiated();
+        }
     }
 }
 
@@ -249,7 +259,12 @@
     // message interrupt is for a transmit message box?
     if ( TRUE == isCANBoxForXmit( srcCANBox ) )
     {
-        transmitNextCANPacket();
+        U32 bytesXmitted = transmitNextCANPacket();
+
+        if ( 0 == bytesXmitted )
+        {
+            signalCANXmitsCompleted();
+        }
     }
     else if ( TRUE == isCANBoxForRecv( srcCANBox ) )
     {
@@ -302,7 +317,12 @@
  *************************************************************************/
 void handleUARTMsgXmitPacketInterrupt( void )
 {
-    transmitNextUARTPacket();
+    U32 bytesXmitted = transmitNextUARTPacket();
+
+    if ( 0 == bytesXmitted )
+    {
+        signalSCI1XmitsCompleted();
+    }
 }
 
 /*************************************************************************
@@ -466,10 +486,11 @@
  * Inputs : Output CAN Comm Buffers
  * Outputs : CAN packet transmit initiated.
  * @param msg : none
- * @return none
+ * @return # of bytes transmitted
  *************************************************************************/
-static void transmitNextCANPacket( void )
+static U32 transmitNextCANPacket( void )
 {
+    U32 result = 0;
     COMM_BUFFER_T buffer = findNextHighestPriorityCANPacketToTransmit();
 
     // if a buffer is found with a packet to transmit, get packet from buffer and transmit it
@@ -483,8 +504,11 @@
         if ( dataSize == CAN_MESSAGE_PAYLOAD_SIZE )
         {
             canTransmit( canREG1, mBox, data );
+            result = CAN_MESSAGE_PAYLOAD_SIZE;
         }
     }
+
+    return result;
 }
 
 /*************************************************************************
@@ -495,10 +519,11 @@
  * Inputs : Output UART Comm Buffer(s)
  * Outputs : UART DMA transmit initiated.
  * @param msg : none
- * @return none
+ * @return # of bytes transmitted
  *************************************************************************/
-static void transmitNextUARTPacket( void )
+static U32 transmitNextUARTPacket( void )
 {
+    U32 result = 0;
     U32 dataPend = numberOfBytesInCommBuffer( COMM_BUFFER_OUT_UART_PC );
     U32 dataSize;
 
@@ -512,8 +537,11 @@
             dmaSetCtrlPacket( DMA_CH3, pcDMAXmitControlRecord );
             dmaSetChEnable( DMA_CH3, DMA_HW );
             setSCI1DMATransmitInterrupt();
+            result = PC_MESSAGE_PACKET_SIZE;
         }
     }
+
+    return result;
 }