Index: firmware/App/Modes/ModeDrain.c
===================================================================
diff -u -r499e5de29e706d09f79ba22511068990c4044e84 -r4c20f6a3d8c8ff33d2dff4ba27e0732c7614378b
--- firmware/App/Modes/ModeDrain.c	(.../ModeDrain.c)	(revision 499e5de29e706d09f79ba22511068990c4044e84)
+++ firmware/App/Modes/ModeDrain.c	(.../ModeDrain.c)	(revision 4c20f6a3d8c8ff33d2dff4ba27e0732c7614378b)
@@ -14,51 +14,138 @@
  *
  **************************************************************************/
 
+#include "DrainPump.h"
+#include "LoadCell.h"
 #include "ModeDrain.h"
 #include "OperationModes.h"
+#include "Reservoirs.h"
+#include "Valves.h"
 
+/**
+ *  @addtogroup DGDrainMode
+ *  @{
+ */
+
+// ********** private definitions **********
+
+#define TARGET_DRAIN_PUMP_RPM       2800                        ///< Target drain pump speed (in RPM).
+
 // ********** private data **********
 
+static DG_DRAIN_STATE_T drainState = DG_DRAIN_STATE_START;      ///< Currently active drain state.
+
 // ********** private function prototypes **********
 
-/*************************************************************************
- * @brief initDrainMode
+static DG_DRAIN_STATE_T handleDrainState( void );
+
+/*********************************************************************//**
+ * @brief
  * The initOpParamsMode function initializes the Drain Mode module.
  * @details
  * Inputs : none
  * Outputs : Operating Parameters Mode module initialized.
- * @param none
  * @return none
  *************************************************************************/
 void initDrainMode( void )
 {
+    drainState = DG_DRAIN_STATE_START;
 }
 
-/*************************************************************************
- * @brief transitionToDrainMode
+/*********************************************************************//**
+ * @brief
  * The transitionToDrainMode function prepares for transition to drain \n
  * mode.
  * @details
  * Inputs : none
  * Outputs :
- * @param none
  * @return none
  *************************************************************************/
 void transitionToDrainMode( void )
 {
+    // re-initialize each time we transition to drain mode
+    initDrainMode();
+
+    // set initial actuator states
+    setValveState( VDR, VALVE_STATE_DRAIN_C_TO_NO );
+    setDrainPumpTargetSpeed( TARGET_DRAIN_PUMP_RPM );
 }
 
-/*************************************************************************
- * @brief execDrainMode
+/*********************************************************************//**
+ * @brief
  * The execDrainMode function executes the Drain Mode state machine.
  * @details
  * Inputs : none
  * Outputs :
- * @param none
- * @return none
+ * @return current state.
  *************************************************************************/
-void execDrainMode( void )
+U32 execDrainMode( void )
 {
+    // execute current drain state
+    switch ( drainState )
+    {
+        case DG_DRAIN_STATE_START:
+            drainState = DG_DRAIN_STATE_DRAIN;
+            break;
 
+        case DG_DRAIN_STATE_DRAIN:
+            drainState = handleDrainState();
+            break;
+
+        default:
+            SET_ALARM_WITH_2_U32_DATA( ALARM_ID_SOFTWARE_FAULT, 0, drainState )     // TODO - add s/w fault enum to 1st data param
+            drainState = DG_DRAIN_STATE_START;
+            break;
+    }
+
+    return drainState;
 }
 
+/*********************************************************************//**
+ * @brief
+ * The handleDrainState function handles the drain state  of the Drain Mode \n
+ * state machine.
+ * @details
+ * Inputs : none
+ * Outputs :
+ * @return the next state
+ *************************************************************************/
+static DG_DRAIN_STATE_T handleDrainState( void )
+{
+    DG_DRAIN_STATE_T result = DG_DRAIN_STATE_DRAIN;
+    LOAD_CELL_ID_T drainWeightLoadCell = LOAD_CELL_A1;
+
+    // determine which load cell to use for drain volume - we want weight of inactive reservoir
+#ifndef BETA_V1_BUILD
+    if ( RESERVOIR_1 == getActiveReservoir() )
+#else
+    if ( RESERVOIR_2 == getActiveReservoir() )
+#endif
+    {
+        drainWeightLoadCell = LOAD_CELL_B1;
+    }
+
+    // if we've reached our target drain to volume (by weight), we're done draining - go back to re-circ mode
+    if ( getReservoirDrainVolumeTargetMl() >= getLoadCellFilteredWeight( drainWeightLoadCell ) )
+    {
+        setDrainPumpTargetSpeed( 0 );
+        requestNewOperationMode( DG_MODE_CIRC );
+    }
+
+    return result;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The getCurrentDrainState function returns the current state of the \n
+ * drain mode.
+ * @details
+ * Inputs : drainState
+ * Outputs : none
+ * @return the current state of drain mode.
+ *************************************************************************/
+DG_DRAIN_STATE_T getCurrentDrainState( void )
+{
+    return drainState;
+}
+
+/**@}*/