Index: firmware/App/Drivers/GPIO.c
===================================================================
diff -u -r3518e8a088c32e75c0c8960d5e629a7401095feb -re8654d6ebf2c76c6bae8e1b465cc1382d205832a
--- firmware/App/Drivers/GPIO.c	(.../GPIO.c)	(revision 3518e8a088c32e75c0c8960d5e629a7401095feb)
+++ firmware/App/Drivers/GPIO.c	(.../GPIO.c)	(revision e8654d6ebf2c76c6bae8e1b465cc1382d205832a)
@@ -79,6 +79,12 @@
 #define SET_SAFETY_SHUTDOWN()               gioSetBit( gioPORTB, SAFETY_GIO_PORT_PIN, PIN_SIGNAL_HIGH )
 #define CLR_SAFETY_SHUTDOWN()               gioSetBit( gioPORTB, SAFETY_GIO_PORT_PIN, PIN_SIGNAL_LOW )
 
+/// Pin SPI3-CS0 - re-purposed as output GPIO for backup alarm audio enable.
+#define BACKUP_AUDIO_ENABLE_SPI3_PORT_MASK    0x00000001
+// Backup alarm audio enable/disable macros
+#define SET_BACKUP_AUDIO_ENABLE()             {mibspiREG3->PC3 |= BACKUP_AUDIO_ENABLE_SPI3_PORT_MASK;}  ///< Macro to enable backup alarm audio.
+#define CLR_BACKUP_AUDIO_ENABLE()             {mibspiREG3->PC3 &= ~BACKUP_AUDIO_ENABLE_SPI3_PORT_MASK;} ///< Macro to disable backup alarm audio.
+
 /*********************************************************************//**
  * @brief
  * The toggleWatchdogPetSignal function toggles the watchdog pet output
@@ -321,4 +327,30 @@
     return signal;
 }
 
+/*********************************************************************//**
+ * @brief
+ * The setAlarmBuzzerSignal function sets the alarm buzzer output signal
+ * on its GPIO pin to HIGH.
+ * @details \b Inputs: none
+ * @details \b Outputs: Alarm buzzer output signal set high
+ * @return none
+ *************************************************************************/
+void setAlarmBuzzerSignal( void )
+{
+    SET_BACKUP_AUDIO_ENABLE()
+}
+
+/*********************************************************************//**
+ * @brief
+ * The clrAlarmBuzzerSignal function sets the alarm buzzer output signal
+ * on its GPIO pin to LOW.
+ * @details \b Inputs: none
+ * @details \b Outputs: Alarm buzzer output signal set low
+ * @return none
+ *************************************************************************/
+void clrAlarmBuzzerSignal( void )
+{
+    CLR_BACKUP_AUDIO_ENABLE()
+}
+
 /**@}*/