AP_Notify: Add tone sequence to alert user when throw detector is armed

Use a medium tempo ascending three tone sequence with sufficient gap to allow the throwing action to be completed without distraction.

libraries/AP_Notify/AP_Notify.h

@@ -60,6 +60,7 @@ public:
         // additional flags
         uint32_t external_leds      : 1;    // 1 if external LEDs are enabled (normally only used for copter)
         uint32_t vehicle_lost       : 1;    // 1 when lost copter tone is requested (normally only used for copter)
+        uint32_t waiting_for_throw  : 1;    // 1 when copter is in THROW mode and waiting to detect the user hand launch
     };
 
     /// notify_events_type - bitmask of active events.

libraries/AP_Notify/ToneAlarm_PX4.cpp

@@ -65,6 +65,8 @@ const ToneAlarm_PX4::Tone ToneAlarm_PX4::_tones[] {
     { "MBNT255>B#8B#8B#8B#8B#8B#8B#8B#8B#8B#8B#8B#8B#8B#8B#8B#8", true },
     #define AP_NOTIFY_PX4_TONE_QUIET_COMPASS_CALIBRATING_CTS 14
     { "MBNT255<C16P2", true },
+    #define AP_NOTIFY_PX4_TONE_WAITING_FOR_THROW 15
+    { "MBNT90L4O2A#O3DFN0N0N0", true},
 };
 
 bool ToneAlarm_PX4::init()
@@ -280,6 +282,15 @@ void ToneAlarm_PX4::update()
         }
     }
 
+    // waiting to be thrown vehicle tone
+    if (flags.waiting_for_throw != AP_Notify::flags.waiting_for_throw) {
+        flags.waiting_for_throw = AP_Notify::flags.waiting_for_throw;
+        if (flags.waiting_for_throw) {
+            play_tone(AP_NOTIFY_PX4_TONE_WAITING_FOR_THROW);
+        } else {
+            stop_cont_tone();
+        }
+    }
 }
 
 #endif // CONFIG_HAL_BOARD == HAL_BOARD_PX4

libraries/AP_Notify/ToneAlarm_PX4.h

@@ -55,6 +55,7 @@ private:
         uint8_t failsafe_radio        : 1;    // 1 if radio failsafe
         uint8_t vehicle_lost          : 1;    // 1 if lost copter tone requested
         uint8_t compass_cal_running   : 1;    // 1 if compass calibration is running
+        uint8_t waiting_for_throw     : 1;    // 1 if waiting for copter throw launch
     } flags;
 
     int8_t _cont_tone_playing;