Index: firmware/App/Modes/ModePreTreat.c
===================================================================
diff -u -r1a685471524555a374854c0c9ec8e208e71fe2df -r4d2dcd2d5ee3c7684be139b7e560b16d8c3abc06
--- firmware/App/Modes/ModePreTreat.c	(.../ModePreTreat.c)	(revision 1a685471524555a374854c0c9ec8e208e71fe2df)
+++ firmware/App/Modes/ModePreTreat.c	(.../ModePreTreat.c)	(revision 4d2dcd2d5ee3c7684be139b7e560b16d8c3abc06)
@@ -15,16 +15,15 @@
 *
 ***************************************************************************/
 
-#include "AirTrap.h"
-#include "AlarmLamp.h"
-#include "BloodFlow.h"
-#include "DialInFlow.h"
-#include "DialOutFlow.h"
-#include "Buttons.h"
+//#include "AirTrap.h"
+//#include "BloodFlow.h"
+//#include "DialInFlow.h"
+//#include "DialOutFlow.h"
+#include "ModePreTreat.h"
 #include "OperationModes.h"
+#include "Prime.h"
 #include "SystemCommMessages.h"
-#include "ModePreTreat.h"
-#include "SystemCommMessages.h"
+
 #ifdef RM46_EVAL_BOARD_TARGET
     #include "Timers.h"
     static U32 start;
@@ -37,9 +36,13 @@
 
 // ********** private data **********
 
-static BOOL treatStartReqReceived = FALSE;                      ///< Flag indicates user requests treatment begin.
+static BOOL treatStartReqReceived = FALSE;                              ///< Flag indicates user requests treatment begin.
 
+static PRE_TREATMENT_MODE_STATE_T currentPreTreatmentState;             ///< Current state of pre-treatment mode state machine.
+
 // ********** private function prototypes **********
+static PRE_TREATMENT_MODE_STATE_T handlePrimeState( void );
+static PRE_TREATMENT_MODE_STATE_T handlePatientConnectionState( void );
 
 /*********************************************************************//**
  * @brief
@@ -50,6 +53,7 @@
 *************************************************************************/
 void initPreTreatmentMode( void )
 {
+    currentPreTreatmentState = PRE_TREATMENT_START_STATE;
 }
 
 /*********************************************************************//**
@@ -78,37 +82,66 @@
 *************************************************************************/
 U32 execPreTreatmentMode( void )
 {
-    BOOL stop = isStopButtonPressed();
-
-#ifndef DISABLE_UI_TREATMENT_WORKFLOW
-    if ( TRUE == treatStartReqReceived )
-#endif
+    // execute mode state machine
+    switch ( currentPreTreatmentState )
     {
-        requestNewOperationMode( MODE_TREA );
+        case PRE_TREATMENT_START_STATE:
+            currentPreTreatmentState = PRE_TREATMENT_WATER_SAMPLE_STATE;
+            break;
+
+        case PRE_TREATMENT_WATER_SAMPLE_STATE:
+            currentPreTreatmentState = PRE_TREATMENT_SELF_TEST_NO_CART_STATE;
+            break;
+
+        case PRE_TREATMENT_SELF_TEST_NO_CART_STATE:
+            currentPreTreatmentState = PRE_TREATMENT_CART_INSTALL_STATE;
+            break;
+
+        case PRE_TREATMENT_CART_INSTALL_STATE:
+            currentPreTreatmentState = PRE_TREATMENT_SELF_TEST_DRY_STATE;
+            break;
+
+        case PRE_TREATMENT_SELF_TEST_DRY_STATE:
+            currentPreTreatmentState = PRE_TREATMENT_PRIME_STATE;
+            break;
+
+        case PRE_TREATMENT_PRIME_STATE:
+            currentPreTreatmentState = handlePrimeState();
+            break;
+
+        case PRE_TREATMENT_SELF_TEST_WET_STATE:
+            currentPreTreatmentState = PRE_TREATMENT_RECIRC_STATE;
+            break;
+
+        case PRE_TREATMENT_RECIRC_STATE:
+            currentPreTreatmentState = PRE_TREATMENT_PATIENT_CONNECTION_STATE;
+            break;
+
+        case PRE_TREATMENT_PATIENT_CONNECTION_STATE:
+            currentPreTreatmentState = handlePatientConnectionState();
+            break;
+
+        default:
+            SET_ALARM_WITH_2_U32_DATA( ALARM_ID_HD_SOFTWARE_FAULT, SW_FAULT_ID_MODE_PRE_TREATMENT_INVALID_STATE, (U32)currentPreTreatmentState )
+            break;
     }
-#ifdef RM46_EVAL_BOARD_TARGET
-    if ( TRUE == didTimeout( start, 5000U ) )
-    {
-        requestNewOperationMode( MODE_TREA );
-    }
-#endif
 
-    return 0; // TODO - return current state
+    return (U32)currentPreTreatmentState;
 }
 
 /*********************************************************************//**
  * @brief
  * The signalUserBeginningTreatment function handles user start of a
  * treatment.
  * @details Inputs: none
- * @details Outputs: requested mode transition to treatment mode
+ * @details Outputs: treatStartReqReceived, send response to treatment start
  * @return TRUE if signal accepted, FALSE if not
  *************************************************************************/
 BOOL signalUserBeginningTreatment( void )
 {
     BOOL result = FALSE;
 
-    if ( MODE_PRET == getCurrentOperationMode() )
+    if ( ( MODE_PRET == getCurrentOperationMode() ) && ( PRE_TREATMENT_PATIENT_CONNECTION_STATE == currentPreTreatmentState ) )
     {
         treatStartReqReceived = TRUE;
         result = TRUE;
@@ -118,4 +151,51 @@
     return result;
 }
 
+/*********************************************************************//**
+ * @brief
+ * The handlePrimeState function handles priming the blood and dialysate circuits.
+ * @details Inputs: none
+ * @details Outputs: requested mode transition to treatment mode
+ * @return current state (sub-mode)
+ *************************************************************************/
+static PRE_TREATMENT_MODE_STATE_T handlePrimeState( void )
+{
+    PRE_TREATMENT_MODE_STATE_T state = PRE_TREATMENT_PRIME_STATE;
+
+    execPrime();
+
+    if ( TRUE == isPrimingPassed() )
+    {
+        state = PRE_TREATMENT_SELF_TEST_WET_STATE;
+    }
+
+    return state;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The handlePatientConnectionState function handles patient connection state
+ * during pre-treatment mode.
+ * @details Inputs: none
+ * @details Outputs: requested mode transition to treatment mode
+ * @return current state (sub-mode)
+ *************************************************************************/
+static PRE_TREATMENT_MODE_STATE_T handlePatientConnectionState( void )
+{
+#ifndef DISABLE_UI_TREATMENT_WORKFLOW
+    if ( TRUE == treatStartReqReceived )
+#endif
+    {
+        requestNewOperationMode( MODE_TREA );
+    }
+#ifdef RM46_EVAL_BOARD_TARGET
+    if ( TRUE == didTimeout( start, 5000U ) )
+    {
+        requestNewOperationMode( MODE_TREA );
+    }
+#endif
+
+    return PRE_TREATMENT_PATIENT_CONNECTION_STATE;
+}
+
 /**@}*/
Index: firmware/App/Modes/Prime.c
===================================================================
diff -u
--- firmware/App/Modes/Prime.c	(revision 0)
+++ firmware/App/Modes/Prime.c	(revision 4d2dcd2d5ee3c7684be139b7e560b16d8c3abc06)
@@ -0,0 +1,54 @@
+/**************************************************************************
+*
+* 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.
+*
+* @file Prime.h
+*
+* @author (last) Quang Nguyen
+* @date (last) 08-Dec-2020
+*
+* @author (original) Quang Nguyen
+* @date (original) 08-Dec-2020
+*
+***************************************************************************/
+
+#include "Prime.h"
+
+/**
+ *  @addtogroup Prime
+ *  @{
+ */
+
+// ********** private definitions **********
+
+// ********** private data **********
+
+static BOOL primeStatus;
+
+// ********** private function prototypes **********
+
+
+void initPrime( void )
+{
+    primeStatus = FALSE;
+}
+
+void transitionToPrime( void )
+{
+}
+
+void execPrime( void )
+{
+}
+
+BOOL isPrimingPassed( void )
+{
+    primeStatus = TRUE;
+    return primeStatus;
+}
+
+
+/**@}*/
Index: firmware/App/Modes/Prime.h
===================================================================
diff -u
--- firmware/App/Modes/Prime.h	(revision 0)
+++ firmware/App/Modes/Prime.h	(revision 4d2dcd2d5ee3c7684be139b7e560b16d8c3abc06)
@@ -0,0 +1,44 @@
+/**************************************************************************
+*
+* 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.
+*
+* @file Prime.h
+*
+* @author (last) Quang Nguyen
+* @date (last) 08-Dec-2020
+*
+* @author (original) Quang Nguyen
+* @date (original) 08-Dec-2020
+*
+***************************************************************************/
+
+#ifndef __PRIME_H__
+#define __PRIME_H__
+
+#include "HDCommon.h"
+#include "HDDefs.h"
+
+/**
+ *  @defgroup Prime Prime
+ *  @brief Prime sub-mode of pre-treatment mode. This sub-mode handles blood and dialysate circuits priming functionality.
+ *
+ *  @addtogroup Prime
+ *  @{
+ */
+
+// ********** public definitions **********
+
+// ********** public function prototypes **********
+
+void initPrime( void );
+void transitionToPrime( void );
+void execPrime( void );
+
+BOOL isPrimingPassed( void );
+
+/**@}*/
+
+#endif
Index: firmware/App/Services/AlarmMgmt.h
===================================================================
diff -u -r933a18d740285e70be9d00696ed0f5a5381bc8e4 -r4d2dcd2d5ee3c7684be139b7e560b16d8c3abc06
--- firmware/App/Services/AlarmMgmt.h	(.../AlarmMgmt.h)	(revision 933a18d740285e70be9d00696ed0f5a5381bc8e4)
+++ firmware/App/Services/AlarmMgmt.h	(.../AlarmMgmt.h)	(revision 4d2dcd2d5ee3c7684be139b7e560b16d8c3abc06)
@@ -215,6 +215,7 @@
     SW_FAULT_ID_AIR_TRAP_INVALID_STATE,
     SW_FAULT_ID_AIR_TRAP_INVALID_LEVEL_SENSOR,                          // 90
     SW_FAULT_ID_DIALYSIS_INVALID_SALINE_BOLUS_STATE,
+    SW_FAULT_ID_MODE_PRE_TREATMENT_INVALID_STATE,
     NUM_OF_SW_FAULT_IDS
 } SW_FAULT_ID_T;