Index: firmware/App/Modes/ModeSolo.c
===================================================================
diff -u -ra504d6899e709d7432af9c055db1bd1fe340d032 -r7d4711edd7b40cd3e29f43e766f79a8a09586fe9
--- firmware/App/Modes/ModeSolo.c	(.../ModeSolo.c)	(revision a504d6899e709d7432af9c055db1bd1fe340d032)
+++ firmware/App/Modes/ModeSolo.c	(.../ModeSolo.c)	(revision 7d4711edd7b40cd3e29f43e766f79a8a09586fe9)
@@ -1,22 +1,24 @@
-/**********************************************************************//**
- *
- *  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 ModeSolo.c
- *
- *  @date 18-Mar-2020
- *  @author S. Nash
- *
- *  @brief Top-level state machine for the standby-solo mode.
- *
- **************************************************************************/
+/**************************************************************************
+*
+* Copyright (c) 2020-2024 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    ModeSolo.c
+*
+* @author  (last)      Michael Garthwaite
+* @date    (last)      16-May-2023
+*
+* @author  (original)  Sean
+* @date    (original)  18-Mar-2020
+*
+***************************************************************************/
 
-#include "OperationModes.h"
-#include "ModeSolo.h"
 #include "CPLD.h"
+#include "ModeSolo.h"
+#include "OperationModes.h"
+#include "SystemComm.h"
 
 /**
  *  @addtogroup DGSoloStandbyMode
@@ -31,12 +33,13 @@
 
 // ********** private function prototypes **********
 
+static DG_SOLO_STANDBY_STATE_T handleIdleDGSoloStandbyState( void );
+
 /*********************************************************************//**
  * @brief
- * The initSoloMode function initializes the Standby-Solo Mode module.
- * @details
- * Inputs : none
- * Outputs : Standby-Solo Mode module initialized.
+ * The initSoloMode function initializes the solo standby mode module.
+ * @details Inputs: none
+ * @details Outputs: Solo standby mode module initialized
  * @return none
  *************************************************************************/
 void initSoloMode( void )
@@ -46,23 +49,25 @@
 
 /*********************************************************************//**
  * @brief
- * The transitionToSoloMode function prepares for transition to standby-solo mode.
- * @details
- * Inputs : none
- * Outputs :
- * @return none
+ * The transitionToSoloMode function prepares for transition to solo standby mode.
+ * @details Inputs: none
+ * @details Outputs: Re-initialized solo standby mode
+ * @return initial state
  *************************************************************************/
-void transitionToSoloMode( void )
+U32 transitionToSoloMode( void )
 {
     initSoloMode();
+    setCurrentSubState( NO_SUB_STATE );
+    setCPLDCleanLEDColor( CPLD_CLEAN_LED_OFF );
+
+    return soloState;
 }
 
 /*********************************************************************//**
  * @brief
- * The execSoloMode function executes the Standby-Solo Mode state machine.
- * @details
- * Inputs : none
- * Outputs :
+ * The execSoloMode function executes the solo standby mode state machine.
+ * @details Inputs: none
+ * @details Outputs: Solo standby mode state machine executed
  * @return current state.
  *************************************************************************/
 U32 execSoloMode( void )
@@ -71,10 +76,15 @@
     switch ( soloState )
     {
         case DG_SOLO_STANDBY_STATE_START:
+            soloState = DG_SOLO_IDLE_STATE;
             break;
 
+        case DG_SOLO_IDLE_STATE:
+            soloState = handleIdleDGSoloStandbyState();
+            break;
+
         default:
-            // TODO - s/w fault
+            SET_ALARM_WITH_2_U32_DATA( ALARM_ID_DG_SOFTWARE_FAULT, SW_FAULT_ID_SOLO_MODE_INVALID_EXEC_STATE, soloState )
             soloState = DG_SOLO_STANDBY_STATE_START;
             break;
     }
@@ -84,13 +94,31 @@
 
 /*********************************************************************//**
  * @brief
- * The getCurrentSoloState function returns the current state of the \n
- * standby-solo mode.
- * @details
- * Inputs : soloState
- * Outputs : none
- * @return the current state of standby-solo mode.
+ * The handleIdleDGSoloStandbyState function handles the idle state of solo standby mode.
+ * @details Inputs: none
+ * @details Outputs: none
+ * @return the next state of solo standby mode.
  *************************************************************************/
+static DG_SOLO_STANDBY_STATE_T handleIdleDGSoloStandbyState( void )
+{
+    DG_SOLO_STANDBY_STATE_T result = DG_SOLO_IDLE_STATE;
+
+    // if HD is on, transition to DG standby mode
+    if ( TRUE == isHDCommunicating() )
+    {
+        requestNewOperationMode( DG_MODE_STAN );
+    }
+
+    return result;
+}
+
+/*********************************************************************//**
+ * @brief
+ * The getCurrentSoloState function returns the current state of solo standby mode.
+ * @details Inputs: soloState
+ * @details Outputs: none
+ * @return the current state of solo standby mode.
+ *************************************************************************/
 DG_SOLO_STANDBY_STATE_T getCurrentSoloState( void )
 {
     return soloState;