Index: firmware/App/Modes/ModeStandby.c
===================================================================
diff -u -r533272e6ef2873fcfe7a41338a6c88c7a601605d -r9ad496e4c3a54e96402afd66955be575bdaa3f57
--- firmware/App/Modes/ModeStandby.c	(.../ModeStandby.c)	(revision 533272e6ef2873fcfe7a41338a6c88c7a601605d)
+++ firmware/App/Modes/ModeStandby.c	(.../ModeStandby.c)	(revision 9ad496e4c3a54e96402afd66955be575bdaa3f57)
@@ -1,25 +1,173 @@
+/**************************************************************************
+*
+* Copyright (c) 2024-2024 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    ModeStandby.c
+*
+* @author  (last)      Michael Garthwaite
+* @date    (last)      28-Feb-2025
+*
+* @author  (original)  Michael Garthwaite
+* @date    (original)  28-Feb-2025
+*
+***************************************************************************/
 
-
 #include "ModeStandby.h"
-
+#include "OperationModes.h"
+#include "PersistentAlarm.h"
+#include "SystemCommRO.h"
+#include "TaskGeneral.h"
 /**
  *  @addtogroup ROStandbyMode
  *  @{
  */
 
+// ********** private definitions **********
+
+// ********** private data **********
+
+static RO_STANDBY_MODE_STATE_T standbyState;                                              ///< Currently active standby state.
+static OVERRIDE_U32_T pendingStartRORequest;                                              ///< Flag indicating DD has requested RO start the generate permeate (Overridable).
+
+// ********** private function prototypes **********
+
+static RO_STANDBY_MODE_STATE_T handleStandbyIdleState( void );
+
+/*********************************************************************//**
+ * @brief
+ * The initStandbyMode function initializes the standby mode unit.
+ * @details \b Inputs: none
+ * @details \b Outputs:unit variables initialized.
+ * @return none
+ *************************************************************************/
 void initStandbyMode( void )
 {
-
+    standbyState = RO_STANDBY_MODE_STATE_IDLE;
+    pendingStartRORequest.data                   = FALSE;
+    pendingStartRORequest.ovData                 = FALSE;
+    pendingStartRORequest.ovInitData             = FALSE;
+    pendingStartRORequest.override               = OVERRIDE_RESET;
 }
 
+/*********************************************************************//**
+ * @brief
+ * The transitionToStandbyMode function prepares for transition to standby mode.
+ * while transition, deenergize all actuators.
+ * @details \b Inputs: none
+ * @details \b Outputs: Re-initialized standby mode
+ * @return initial state
+ *************************************************************************/
 U32  transitionToStandbyMode( void )
 {
-    return 0;
+    initStandbyMode();
+
+    return standbyState;
 }
 
+/*********************************************************************//**
+ * @brief
+ * The execStandbyMode function executes the standby mode state machine.
+ * @details \b Inputs: none
+ * @details \b Outputs: Standby mode state machine executed
+ * @details \b Alarm: ALARM_ID_RO_SOFTWARE_FAULT if standbyState is invalid.
+ * @return current state
+ *************************************************************************/
 U32  execStandbyMode( void )
 {
-    return 0;
+
+    // execute current Standby state
+    switch ( standbyState )
+    {
+        case RO_STANDBY_MODE_STATE_IDLE:
+            standbyState = handleStandbyIdleState();
+            break;
+
+        default:
+            SET_ALARM_WITH_2_U32_DATA( ALARM_ID_RO_SOFTWARE_FAULT, SW_FAULT_ID_MODE_STANDBY_INVALID_STATE, standbyState )
+            standbyState = RO_STANDBY_MODE_STATE_IDLE;
+            break;
+    }
+
+    return standbyState;
 }
 
+/*********************************************************************//**
+ * @brief
+ * The handleStandbyIdleState function executes the idle state of the
+ * standby mode state machine.
+ * @details \b Inputs:
+ * @details \b Outputs:
+ * @details \b Message \Sent:
+ * @return the next state
+ *************************************************************************/
+static RO_STANDBY_MODE_STATE_T handleStandbyIdleState( void )
+{
+    RO_STANDBY_MODE_STATE_T state = RO_STANDBY_MODE_STATE_IDLE;
+
+    if ( TRUE == getU32OverrideValue( &pendingStartRORequest ) )
+    {
+        pendingStartRORequest.data = FALSE;
+        requestNewOperationMode( RO_MODE_GEN_PERM );
+    }
+
+    return state;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The getCurrentStandbyState function returns the current state of standby mode.
+ * @details \b Inputs: standbyState
+ * @details \b Outputs: none
+ * @return the current state of standby mode.
+ *************************************************************************/
+RO_STANDBY_MODE_STATE_T getCurrentStandbyState( void )
+{
+    return standbyState;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The requestROStart function handles an DD request to start (go to gen permeate mode).
+ * @details \b Inputs: standbyState
+ * @details \b Outputs: pendingStartRORequest
+ * @return TRUE if request accepted, FALSE if not.
+ *************************************************************************/
+BOOL requestROStart( void )
+{
+    BOOL result = FALSE;
+
+    if ( RO_STANDBY_MODE_STATE_IDLE == standbyState )
+    {
+        result                     = TRUE;
+        pendingStartRORequest.data = TRUE;
+    }
+
+    return result;
+}
+
+/*************************************************************************
+ *                       TEST SUPPORT FUNCTIONS
+ *************************************************************************/
+
+
+/*********************************************************************//**
+ * @brief
+ * The testROstartGenPermeateOverride function sets the override value
+ * to start the generate permeate operation mode.
+ * @details Inputs: pendingStartRORequest
+ * @details Outputs: pendingStartRORequest
+ * @param message Override message from Dialin which includes the flag
+ * to override the operation mode.
+ * @return TRUE if override successful, FALSE if not
+ *************************************************************************/
+BOOL testROstartGenPermeateOverride( MESSAGE_T *message )
+{
+    BOOL result = u32Override( message, &pendingStartRORequest, FALSE, TRUE );
+
+    return result;
+}
+
 /**@}*/