AP_Notify: added NTZ_BUZZ_VOLUME parameter

it is fairly non-linear, but does work

libraries/AP_Notify/AP_Notify.cpp

@@ -158,6 +158,13 @@ const AP_Param::GroupInfo AP_Notify::var_info[] = {
     AP_GROUPINFO("BUZZ_ON_LVL", 7, AP_Notify, _buzzer_level, 1),
 #endif
 
+    // @Param: BUZZ_VOLUME
+    // @DisplayName: Buzzer volume
+    // @Description: Enable or disable the buzzer.
+    // @Range: 0 100
+    // @Units: %
+    AP_GROUPINFO("BUZZ_VOLUME", 8, AP_Notify, _buzzer_volume, 100),
+    
     AP_GROUPEND
 };
 

libraries/AP_Notify/AP_Notify.h

@@ -158,6 +158,7 @@ public:
     static const struct AP_Param::GroupInfo var_info[];
     uint8_t get_buzz_pin() const  { return _buzzer_pin; }
     uint8_t get_buzz_level() const  { return _buzzer_level; }
+    uint8_t get_buzz_volume() const  { return _buzzer_volume; }
 
 #if CONFIG_HAL_BOARD == HAL_BOARD_SITL
     HAL_Semaphore sf_window_mutex;
@@ -181,6 +182,7 @@ private:
     AP_Int8 _buzzer_pin;
     AP_Int32 _led_type;
     AP_Int8 _buzzer_level;
+    AP_Int8 _buzzer_volume;
 
     char _send_text[NOTIFY_TEXT_BUFFER_SIZE];
     uint32_t _send_text_updated_millis; // last time text changed

libraries/AP_Notify/MMLPlayer.cpp

@@ -4,6 +4,7 @@
 #include <math.h>
 #include <AP_HAL/AP_HAL.h>
 #include <AP_Math/AP_Math.h>
+#include <AP_Notify/AP_Notify.h>
 
 #if HAL_WITH_UAVCAN
 #include <AP_UAVCAN/AP_UAVCAN.h>
@@ -297,6 +298,8 @@ void MMLPlayer::next_action()
 
     float note_frequency = 880.0f * expf(logf(2.0f) * ((int)note - 46) / 12.0f);
     float note_volume = _volume/255.0f;
+    note_volume *= AP::notify().get_buzz_volume() * 0.01;
+    note_volume = constrain_float(note_volume, 0, 1);
 
     note_frequency = constrain_float(note_frequency, 10, 22000);