Index: firmware/App/Modes/Prime.c
===================================================================
diff -u -r4d2dcd2d5ee3c7684be139b7e560b16d8c3abc06 -r604a7f0b5ffb72a8c5989f7476e4423181f54e4d
--- firmware/App/Modes/Prime.c	(.../Prime.c)	(revision 4d2dcd2d5ee3c7684be139b7e560b16d8c3abc06)
+++ firmware/App/Modes/Prime.c	(.../Prime.c)	(revision 604a7f0b5ffb72a8c5989f7476e4423181f54e4d)
@@ -24,31 +24,209 @@
 
 // ********** private definitions **********
 
+#define BLOOD_PUMP_FLOW_RATE_PURGE_AIR          100                                             ///< Blood pump flow rate during prime purge air state.
+#define BLOOD_PUMP_FLOW_RATE_COLLECT_AIR        300                                             ///< Blood pump flow rate during prime collect air state.
+#define NO_AIR_DETECTED_COUNT                   ( 5 * MS_PER_SEC / TASK_GENERAL_INTERVAL )      ///< No air detected time period count.
+
 // ********** private data **********
 
-static BOOL primeStatus;
+static PRE_TREATMENT_PRIME_STATE_T currentPrimeState;                                           ///< Current state of the prime sub-mode state machine.
+static BOOL isPrimeCompleted;                                                                   ///< Status if prime sequence has been completed.
+static BOOL primeStartReqReceived;                                                              ///< Flag to indicate if a request to start priming has been received.
+static U32 noAirDetectedTimerCounter;                                                           ///< No air detected timer counter.
 
 // ********** private function prototypes **********
 
+static void purgeAirValvesBloodPumpControl( void );
 
+static PRE_TREATMENT_PRIME_STATE_T handlePrimeSalineSetupState( void );
+static PRE_TREATMENT_PRIME_STATE_T handlePrimePurgeAirState( void );
+static PRE_TREATMENT_PRIME_STATE_T handlePrimeCircBloodCircuitState( void );
+static PRE_TREATMENT_PRIME_STATE_T handlePrimeDialysateDialyzerState( void );
+
+/*********************************************************************//**
+ * @brief
+ * The initPrime function initializes the prime sub-mode module.
+ * This function will reset anything required before the start of priming sequence.
+ * @details Inputs: none
+ * @details Outputs: Prime sub-mode module initialized.
+ * @return none
+ *************************************************************************/
 void initPrime( void )
 {
-    primeStatus = FALSE;
+    transitionToPrime();
 }
 
+/*********************************************************************//**
+ * @brief
+ * The transitionToPrime function prepares for transition to prime sub-mode.
+ * This function will reset anything required before the start of priming sequence.
+ * @details Inputs: none
+ * @details Outputs: none
+ * @return none
+ *************************************************************************/
 void transitionToPrime( void )
 {
+    currentPrimeState = PRIME_START_STATE;
+    isPrimeCompleted = FALSE;
+    primeStartReqReceived = FALSE;
 }
 
+/*********************************************************************//**
+ * @brief
+ * The execPrime function executes the prime sub-mode state machine.
+ * @details Inputs: currentPrimeState
+ * @details Outputs: currentPrimeState
+ * @return none
+ *************************************************************************/
 void execPrime( void )
 {
+    // execute prime sub-mode state machine
+    switch ( currentPrimeState )
+    {
+        case PRIME_START_STATE:
+            currentPrimeState = PRIME_SALINE_SETUP_STATE;
+            break;
+
+        case PRIME_SALINE_SETUP_STATE:
+            currentPrimeState = handlePrimeSalineSetupState();
+            break;
+
+        case PRIME_SALINE_PURGE_AIR_STATE:
+            currentPrimeState = handlePrimePurgeAirState();
+            break;
+
+        case PRIME_SALINE_CIRC_BLOOD_CIRCUIT_STATE:
+            currentPrimeState = handlePrimeCircBloodCircuitState();
+            break;
+
+        case PRIME_DIALYSATE_DIALYZER_STATE:
+            currentPrimeState = handlePrimeDialysateDialyzerState();
+            break;
+    }
 }
 
+/*********************************************************************//**
+ * @brief
+ * The isPrimingPassed function returns the status of prime mode.
+ * @details Inputs: none
+ * @details Outputs: none
+ * @return TRUE if prime has completed, otherwise FALSE
+ *************************************************************************/
 BOOL isPrimingPassed( void )
 {
-    primeStatus = TRUE;
-    return primeStatus;
+    return isPrimeCompleted;
 }
 
+/*********************************************************************//**
+ * @brief
+ * The purgeAirValvesBloodPumpControl function controls valves and blood pump
+ * to purge air.
+ * @details Inputs: none
+ * @details Outputs: run blood pump, close VDI, VDO, VBA and VBV valves, open VBT valve
+ * @return current state (sub-mode)
+ *************************************************************************/
+static void purgeAirValvesBloodPumpControl( void )
+{
+    setValvePosition( VDI, VALVE_POSITION_C_CLOSE );
+    setValvePosition( VDO, VALVE_POSITION_C_CLOSE );
+    setValvePosition( VBA, VALVE_POSITION_C_CLOSE );
+    setValvePosition( VBV, VALVE_POSITION_C_CLOSE );
+    // TODO: setValvePosition( VBT, VALVE_POSITION_B_OPEN );
 
+    setBloodPumpTargetFlowRate( BLOOD_PUMP_FLOW_RATE_PURGE_AIR, MOTOR_DIR_FORWARD, PUMP_CONTROL_MODE_OPEN_LOOP );
+}
+
+/*********************************************************************//**
+ * @brief
+ * The handlePrimeSalineSetupState function checks user's request to start
+ * priming.
+ * @details Inputs: primeStartReqReceived
+ * @details Outputs: control valves to purge air
+ * @return current state (sub-mode)
+ *************************************************************************/
+static PRE_TREATMENT_PRIME_STATE_T handlePrimeSalineSetupState( void )
+{
+    PRE_TREATMENT_PRIME_STATE_T state = PRIME_SALINE_SETUP_STATE;
+
+    if ( TRUE == primeStartReqReceived )
+    {
+        purgeAirValvesBloodPumpControl();
+        state = PRIME_SALINE_PURGE_AIR_STATE;
+    }
+
+    return state;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The handlePrimePurgeAirState function checks for air trap level and moves
+ * to blood circuit circulation state if fluid is detected at upper sensor.
+ * @details Inputs: air trap levels
+ * @details Outputs: runs blood pump, control valves to trap air
+ * @return current state (sub-mode)
+ *************************************************************************/
+static PRE_TREATMENT_PRIME_STATE_T handlePrimePurgeAirState( void )
+{
+    PRE_TREATMENT_PRIME_STATE_T state = PRIME_SALINE_PURGE_AIR_STATE;
+
+    if ( AIR_TRAP_LEVEL_FLUID == getAirTrapLevel( AIR_TRAP_LEVEL_SENSOR_UPPER ) )
+    {
+        setValvePosition( VDI, VALVE_POSITION_C_CLOSE );
+        setValvePosition( VDO, VALVE_POSITION_C_CLOSE );
+        setValvePosition( VBA, VALVE_POSITION_B_OPEN );
+        setValvePosition( VBV, VALVE_POSITION_B_OPEN );
+        // TODO: setValvePosition( VBT, VALVE_POSITION_C_CLOSE );
+
+        setBloodPumpTargetFlowRate( BLOOD_PUMP_FLOW_RATE_COLLECT_AIR, MOTOR_DIR_FORWARD, PUMP_CONTROL_MODE_OPEN_LOOP );
+        noAirDetectedTimerCounter = 0;
+        state = PRIME_SALINE_CIRC_BLOOD_CIRCUIT_STATE;
+    }
+
+    return state;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The handlePrimeCircBloodCircuitState function checks for air trap level and
+ * return to purge air state if air is detected at lower sensor. If no air
+ * detected for a period of time, the blood pump is stopped.
+ * @details Inputs: air trap levels
+ * @details Outputs: stop blood pump, control valves to purge air
+ * @return current state (sub-mode)
+ *************************************************************************/
+static PRE_TREATMENT_PRIME_STATE_T handlePrimeCircBloodCircuitState( void )
+{
+    PRE_TREATMENT_PRIME_STATE_T state = PRIME_SALINE_CIRC_BLOOD_CIRCUIT_STATE;
+
+    if ( AIR_TRAP_LEVEL_AIR == getAirTrapLevel( AIR_TRAP_LEVEL_SENSOR_LOWER ) )
+    {
+        purgeAirValvesBloodPumpControl();
+        state = PRIME_SALINE_PURGE_AIR_STATE;
+    }
+
+    if ( ++noAirDetectedTimerCounter > NO_AIR_DETECTED_COUNT )
+    {
+        signalBloodPumpHardStop();
+        state = PRIME_DIALYSATE_DIALYZER_STATE;
+    }
+
+    return state;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The handlePrimeDialysateDialyzerState function handles priming for
+ * dialysate dialyzer fluid path.
+ * @details Inputs: none
+ * @details Outputs: isPrimeCompleted
+ * @return current state (sub-mode)
+ *************************************************************************/
+static PRE_TREATMENT_PRIME_STATE_T handlePrimeDialysateDialyzerState( void )
+{
+    // TODO: Add priming for dialysate circuit
+    isPrimeCompleted = TRUE;
+    return PRIME_DIALYSATE_DIALYZER_STATE;
+}
+
 /**@}*/