Index: firmware/App/Services/DDInterface.c
===================================================================
diff -u -re9e339870c5ed01230963f00d400331ab879c91f -r6f876554db45a19590eaf2122ef47e33f7a7d69b
--- firmware/App/Services/DDInterface.c	(.../DDInterface.c)	(revision e9e339870c5ed01230963f00d400331ab879c91f)
+++ firmware/App/Services/DDInterface.c	(.../DDInterface.c)	(revision 6f876554db45a19590eaf2122ef47e33f7a7d69b)
@@ -45,6 +45,7 @@
 
 static BOOL ddOpModeDataFreshFlag;                                          ///< Flag to signal the handleDDOpMode() to process fresh dd op mode data.
 static BOOL ddDialysatePressureFreshFlag;                                   ///< Flag to signal
+static BOOL dialysateGoodToDeliver;                                         ///< Flag indicates dialysate readiness (from GEN_DIALYSATE_MODE_DATA_T broadcast).
 
 static DIALYSATE_DELIVERY_REQ_PAYLOAD_T dialysateDeliveryCmdSet;            ///< Set of dialysate delivery parameters to send to the DD during treatment.
 
@@ -73,6 +74,7 @@
 
     ddOpModeDataFreshFlag                   = FALSE;
     ddDialysatePressureFreshFlag            = FALSE;
+    dialysateGoodToDeliver                  = FALSE;
 
     resetDDInterface();
 
@@ -109,6 +111,7 @@
     dialysateDeliveryCmdSet.bicarbConvFactor  = 0.0F;
     dialysateDeliveryCmdSet.sodium            = 0;
     dialysateDeliveryCmdSet.bicarbonate       = 0;
+    dialysateDeliveryCmdSet.substitutionRate  = 0.0F;
 }
 
 /**********************************************************************//**
@@ -312,6 +315,7 @@
     dialysateDeliveryCmdSet.bicarbConvFactor = bicarbConvFactor;
     dialysateDeliveryCmdSet.sodium           = sodium;
     dialysateDeliveryCmdSet.bicarbonate      = bicarbonate;
+    dialysateDeliveryCmdSet.substitutionRate = 0.0F;
 
 #ifndef TEST_UI_ONLY
     sendMessage( MSG_ID_DD_GEN_DIALYSATE_REQUEST_DATA, COMM_BUFFER_OUT_CAN_TD_2_DD, (U08*)(&dialysateDeliveryCmdSet), sizeof( DIALYSATE_DELIVERY_REQ_PAYLOAD_T ) );
@@ -509,7 +513,79 @@
 //    }
 }
 
+/*********************************************************************//**
+ * @brief
+ * The cmdSubstitutionRate function sends a generate dialysate command to
+ * the DD with a given substitution (D92) pump rate for HDF / HD-online
+ * fluid bolus delivery.
+ * @details \b Message \b Sent: MSG_ID_DD_GEN_DIALYSATE_REQUEST_DATA
+ * @details \b Inputs: none
+ * @details \b Outputs: dialysateDeliveryCmdSet
+ * @param qs Target substitution flow rate (mL/min)
+ * @return none
+ *************************************************************************/
+void cmdSubstitutionRate( F32 qs )
+{
+    if ( TRUE == dialysateDeliveryCmdSet.start )
+    {
+        dialysateDeliveryCmdSet.substitutionRate = qs;
+#ifndef TEST_UI_ONLY
+        sendMessage( MSG_ID_DD_GEN_DIALYSATE_REQUEST_DATA, COMM_BUFFER_OUT_CAN_TD_2_DD, (U08*)(&dialysateDeliveryCmdSet), sizeof( DIALYSATE_DELIVERY_REQ_PAYLOAD_T ) );
+#endif
+    }
+    else
+    {
+        // TODO - s/w fault?
+    }
+}
 
+/*********************************************************************//**
+ * @brief
+ * The isDialysateGoodToDeliver function returns the latest DD-reported
+ * dialysate readiness flag, cached from the DD gen-dialysate state
+ * broadcast. Used by the fluid bolus service to gate substitution bolus
+ * start and to monitor during delivery.
+ * @details \b Inputs: dialysateGoodToDeliver
+ * @details \b Outputs: none
+ * @return TRUE if dialysate is ready to deliver per DD, FALSE otherwise.
+**************************************************************************/
+BOOL isDialysateGoodToDeliver( void )
+{
+    return dialysateGoodToDeliver;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The setGenDialysateModeData function processes the DD generate-dialysate
+ * mode data broadcast and caches the dialysate readiness flag.
+ * @details \b Alarm: ALARM_ID_TD_SOFTWARE_FAULT if message payload invalid.
+ * @details \b Inputs: none
+ * @details \b Outputs: dialysateGoodToDeliver
+ * @param message Pointer to DD generate-dialysate state broadcast message.
+ * @return TRUE if message handled successfully, FALSE if not.
+ *************************************************************************/
+BOOL setGenDialysateModeData( MESSAGE_T *message )
+{
+    BOOL result = FALSE;
+    GEN_DIALYSATE_MODE_DATA_T payload;
+
+    if ( sizeof( GEN_DIALYSATE_MODE_DATA_T ) == message->hdr.payloadLen )
+    {
+        memcpy( &payload, &message->payload[0], sizeof( GEN_DIALYSATE_MODE_DATA_T ) );
+        dialysateGoodToDeliver = payload.isDialysateGoodtoDeliver;
+        result = TRUE;
+    }
+    else
+    {
+#ifndef TEST_UI_ONLY
+        SET_ALARM_WITH_2_U32_DATA( ALARM_ID_TD_SOFTWARE_FAULT, SW_FAULT_ID_INVALID_DD_GEN_DIALYSATE_DATA, (U32)message->hdr.payloadLen );
+#endif
+    }
+
+    return result;
+}
+
+
 /*************************************************************************
  *                       TEST SUPPORT FUNCTIONS
  *************************************************************************/