Index: firmware/App/Services/SystemComm.h
===================================================================
diff -u -reff7b1575f008f81b29ef906f6346fac6012d3ab -re5bb82cad756fbb10f04d576dffd499df78f6b35
--- firmware/App/Services/SystemComm.h	(.../SystemComm.h)	(revision eff7b1575f008f81b29ef906f6346fac6012d3ab)
+++ firmware/App/Services/SystemComm.h	(.../SystemComm.h)	(revision e5bb82cad756fbb10f04d576dffd499df78f6b35)
@@ -1,6 +1,6 @@
 /**************************************************************************
  *
- *  Copyright (c) 2019-2019 Diality Inc. - All Rights Reserved.
+ *  Copyright (c) 2019-2020 Diality Inc. - All Rights Reserved.
  *
  *  THIS CODE MAY NOT BE COPIED OR REPRODUCED IN ANY FORM, IN PART OR IN
  *  WHOLE, WITHOUT THE EXPLICIT PERMISSION OF THE COPYRIGHT OWNER.
@@ -17,18 +17,25 @@
 #ifndef __SYSTEM_COMM_H__
 #define __SYSTEM_COMM_H__
 
-#include "Common.h"
+#include "../HDCommon.h"
 #include "CommBuffers.h"
+#include "MsgQueues.h"
 
 // ********** public definitions **********
 
 #define MESSAGE_SYNC_BYTE           0xA5
 
-#define CAN_MESSAGE_CARGO_SIZE      8
+#define CAN_MESSAGE_PAYLOAD_SIZE    8
 #define PC_MESSAGE_PACKET_SIZE      8
 
-typedef COMM_BUFFER_T   CAN_MESSAGE_BOX_T;       // the first 10 comm buffers align with the 10 active CAN message boxes
+#define MSG_ID_ACK                  0xFFFF
+#define MSG_ACK_BIT                 0x8000
+#define MAX_MSG_SEQ_NO              0x7FFF
+#define MIN_MSG_SEQ_NO              0x0001
+#define MAX_ACK_MSG_SIZE            ( sizeof( MESSAGE_WRAPPER_T ) + 1 + CAN_MESSAGE_PAYLOAD_SIZE )  // must hold full (wrapped) message + sync + any CAN padding
 
+typedef COMM_BUFFER_T   CAN_MESSAGE_BOX_T;       // the first 12 comm buffers align with the 12 active CAN message boxes
+
 // ********** public function prototypes **********
 
 void initSystemComm( void );
@@ -37,5 +44,13 @@
 void handleCANMsgInterrupt( CAN_MESSAGE_BOX_T srcCANBox );
 void handleUARTMsgRecvPacketInterrupt( void );
 void handleUARTMsgXmitPacketInterrupt( void );
+void checkInFromDG( void );
+void checkInFromUI( void );
+BOOL isDGCommunicating( void );
+BOOL isUICommunicating( void );
+BOOL uiCommunicated( void );
+#ifndef ACK_NOT_IMPLEMENTED
+BOOL addMsgToPendingACKList( MESSAGE_T *msg, COMM_BUFFER_T channel, U08 *msgData, U32 len );
+#endif
 
 #endif