Index: firmware/App/Services/SystemComm.h
===================================================================
diff -u -r52863cba9685f31136ab3f4b4764a17ccf34fc05 -r6c60d0d0300828750c76f2e397d4e7ccaa84bbb2
--- firmware/App/Services/SystemComm.h	(.../SystemComm.h)	(revision 52863cba9685f31136ab3f4b4764a17ccf34fc05)
+++ firmware/App/Services/SystemComm.h	(.../SystemComm.h)	(revision 6c60d0d0300828750c76f2e397d4e7ccaa84bbb2)
@@ -19,6 +19,7 @@
 
 #include "Common.h"
 #include "CommBuffers.h"
+#include "MsgQueues.h"
 
 // ********** public definitions **********
 
@@ -27,6 +28,12 @@
 #define CAN_MESSAGE_PAYLOAD_SIZE    8
 #define PC_MESSAGE_PACKET_SIZE      8
 
+#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 **********
@@ -42,5 +49,8 @@
 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