More Beeper clean up.

Centralised beep code to lcd_buzz().
From gcode_M300() and lcd_quick_feedback().

Enforced max. duration for M300 to 5 seconds.

Corrected description in 'Configuration.h'

LCD_FEEDBACK_FREQUENCY_HZ 0 gives now a silent delay of
LCD_FEEDBACK_FREQUENCY_DURATION_MS.

Marlin/Configuration.h

 //#define ENCODER_STEPS_PER_MENU_ITEM 5 // Set according to ENCODER_PULSES_PER_STEP or your liking
 //#define ULTIMAKERCONTROLLER //as available from the Ultimaker online store.
 //#define ULTIPANEL  //the UltiPanel as on Thingiverse
-//#define LCD_FEEDBACK_FREQUENCY_HZ 1000	// this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
 //#define LCD_FEEDBACK_FREQUENCY_DURATION_MS 100 // the duration the buzzer plays the UI feedback sound. ie Screen Click
-                                               // 0 to disable buzzer feedback  
-
+//#define LCD_FEEDBACK_FREQUENCY_HZ 1000         // this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
+                                                 // 0 to disable buzzer feedback. Test with M300 S<frequency Hz> P<duration ms>
 // PanelOne from T3P3 (via RAMPS 1.4 AUX2/AUX3)
 // http://reprap.org/wiki/PanelOne
 //#define PANEL_ONE
 
 // The RepRapDiscount Smart Controller (white PCB)
 // http://reprap.org/wiki/RepRapDiscount_Smart_Controller
-//#define REPRAP_DISCOUNT_SMART_CONTROLLER
+#define REPRAP_DISCOUNT_SMART_CONTROLLER
 
 // The GADGETS3D G3D LCD/SD Controller (blue PCB)
 // http://reprap.org/wiki/RAMPS_1.3/1.4_GADGETS3D_Shield_with_Panel

Marlin/Marlin_main.cpp

   inline void gcode_M300() {
     uint16_t beepS = code_seen('S') ? code_value_short() : 110;
     uint32_t beepP = code_seen('P') ? code_value_long() : 1000;
-    if (beepS > 0) {
-      #if BEEPER > 0
-        tone(BEEPER, beepS);
-        delay(beepP);
-        noTone(BEEPER);
-      #elif defined(ULTRALCD)
-        lcd_buzz(beepP, beepS);
-      #elif defined(LCD_USE_I2C_BUZZER)
-        lcd_buzz(beepP, beepS);
-      #endif
-    }
-    else {
-      delay(beepP);
-    }
+    if (beepP > 5000) beepP = 5000; // limit to 5 seconds
+    lcd_buzz(beepP, beepS);
   }
 
 #endif // BEEPER>0 || ULTRALCD || LCD_USE_I2C_BUZZER

Marlin/configurator/config/Configuration.h

 //#define ENCODER_STEPS_PER_MENU_ITEM 5 // Set according to ENCODER_PULSES_PER_STEP or your liking
 //#define ULTIMAKERCONTROLLER //as available from the Ultimaker online store.
 //#define ULTIPANEL  //the UltiPanel as on Thingiverse
-//#define LCD_FEEDBACK_FREQUENCY_HZ 1000	// this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
 //#define LCD_FEEDBACK_FREQUENCY_DURATION_MS 100 // the duration the buzzer plays the UI feedback sound. ie Screen Click
-                                               // 0 to disable buzzer feedback  
+//#define LCD_FEEDBACK_FREQUENCY_HZ 1000         // this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
+                                                 // 0 to disable buzzer feedback. Test with M300 S<frequency Hz> P<duration ms>
 
 // PanelOne from T3P3 (via RAMPS 1.4 AUX2/AUX3)
 // http://reprap.org/wiki/PanelOne

Marlin/example_configurations/Felix/Configuration.h

 //#define ENCODER_STEPS_PER_MENU_ITEM 5 // Set according to ENCODER_PULSES_PER_STEP or your liking
 //#define ULTIMAKERCONTROLLER //as available from the Ultimaker online store.
 //#define ULTIPANEL  //the UltiPanel as on Thingiverse
-//#define LCD_FEEDBACK_FREQUENCY_HZ 1000	// this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
 //#define LCD_FEEDBACK_FREQUENCY_DURATION_MS 100 // the duration the buzzer plays the UI feedback sound. ie Screen Click
-                                               // 0 to disable buzzer feedback  
+//#define LCD_FEEDBACK_FREQUENCY_HZ 1000         // this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
+                                                 // 0 to disable buzzer feedback. Test with M300 S<frequency Hz> P<duration ms>
 
 // PanelOne from T3P3 (via RAMPS 1.4 AUX2/AUX3)
 // http://reprap.org/wiki/PanelOne

Marlin/example_configurations/Felix/Configuration_DUAL.h

 //#define ENCODER_STEPS_PER_MENU_ITEM 5 // Set according to ENCODER_PULSES_PER_STEP or your liking
 //#define ULTIMAKERCONTROLLER //as available from the Ultimaker online store.
 //#define ULTIPANEL  //the UltiPanel as on Thingiverse
-//#define LCD_FEEDBACK_FREQUENCY_HZ 1000	// this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
 //#define LCD_FEEDBACK_FREQUENCY_DURATION_MS 100 // the duration the buzzer plays the UI feedback sound. ie Screen Click
-                                               // 0 to disable buzzer feedback  
+//#define LCD_FEEDBACK_FREQUENCY_HZ 1000         // this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
+                                                 // 0 to disable buzzer feedback. Test with M300 S<frequency Hz> P<duration ms>
 
 // PanelOne from T3P3 (via RAMPS 1.4 AUX2/AUX3)
 // http://reprap.org/wiki/PanelOne

Marlin/example_configurations/Hephestos/Configuration.h

 //#define ENCODER_STEPS_PER_MENU_ITEM 5 // Set according to ENCODER_PULSES_PER_STEP or your liking
 //#define ULTIMAKERCONTROLLER //as available from the Ultimaker online store.
 //#define ULTIPANEL  //the UltiPanel as on Thingiverse
-//#define LCD_FEEDBACK_FREQUENCY_HZ 1000	// this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
 //#define LCD_FEEDBACK_FREQUENCY_DURATION_MS 100 // the duration the buzzer plays the UI feedback sound. ie Screen Click
-                                               // 0 to disable buzzer feedback  
+//#define LCD_FEEDBACK_FREQUENCY_HZ 1000         // this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
+                                                 // 0 to disable buzzer feedback. Test with M300 S<frequency Hz> P<duration ms>
 
 // PanelOne from T3P3 (via RAMPS 1.4 AUX2/AUX3)
 // http://reprap.org/wiki/PanelOne

Marlin/example_configurations/K8200/Configuration.h

 //#define ENCODER_STEPS_PER_MENU_ITEM 5 // Set according to ENCODER_PULSES_PER_STEP or your liking
 #define ULTIMAKERCONTROLLER //as available from the Ultimaker online store.
 //#define ULTIPANEL  //the UltiPanel as on Thingiverse
-//#define LCD_FEEDBACK_FREQUENCY_HZ 1000	// this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
 //#define LCD_FEEDBACK_FREQUENCY_DURATION_MS 100 // the duration the buzzer plays the UI feedback sound. ie Screen Click
-                                               // 0 to disable buzzer feedback  
+//#define LCD_FEEDBACK_FREQUENCY_HZ 1000         // this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
+                                                 // 0 to disable buzzer feedback. Test with M300 S<frequency Hz> P<duration ms>
 
 // PanelOne from T3P3 (via RAMPS 1.4 AUX2/AUX3)
 // http://reprap.org/wiki/PanelOne

Marlin/example_configurations/SCARA/Configuration.h

 //#define ENCODER_STEPS_PER_MENU_ITEM 5 // Set according to ENCODER_PULSES_PER_STEP or your liking
 //#define ULTIMAKERCONTROLLER //as available from the Ultimaker online store.
 //#define ULTIPANEL  //the UltiPanel as on Thingiverse
-//#define LCD_FEEDBACK_FREQUENCY_HZ 1000	// this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
 //#define LCD_FEEDBACK_FREQUENCY_DURATION_MS 100 // the duration the buzzer plays the UI feedback sound. ie Screen Click
-                                               // 0 to disable buzzer feedback  
+//#define LCD_FEEDBACK_FREQUENCY_HZ 1000         // this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
+                                                 // 0 to disable buzzer feedback. Test with M300 S<frequency Hz> P<duration ms>
 
 // PanelOne from T3P3 (via RAMPS 1.4 AUX2/AUX3)
 // http://reprap.org/wiki/PanelOne

Marlin/example_configurations/WITBOX/Configuration.h

 //#define ENCODER_STEPS_PER_MENU_ITEM 5 // Set according to ENCODER_PULSES_PER_STEP or your liking
 //#define ULTIMAKERCONTROLLER //as available from the Ultimaker online store.
 //#define ULTIPANEL  //the UltiPanel as on Thingiverse
-//#define LCD_FEEDBACK_FREQUENCY_HZ 1000	// this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
 //#define LCD_FEEDBACK_FREQUENCY_DURATION_MS 100 // the duration the buzzer plays the UI feedback sound. ie Screen Click
-                                               // 0 to disable buzzer feedback  
+//#define LCD_FEEDBACK_FREQUENCY_HZ 1000         // this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
+                                                 // 0 to disable buzzer feedback. Test with M300 S<frequency Hz> P<duration ms>
 
 // PanelOne from T3P3 (via RAMPS 1.4 AUX2/AUX3)
 // http://reprap.org/wiki/PanelOne

Marlin/example_configurations/delta/generic/Configuration.h

 //#define ENCODER_STEPS_PER_MENU_ITEM 5 // Set according to ENCODER_PULSES_PER_STEP or your liking
 //#define ULTIMAKERCONTROLLER //as available from the Ultimaker online store.
 //#define ULTIPANEL  //the UltiPanel as on Thingiverse
-//#define LCD_FEEDBACK_FREQUENCY_HZ 1000	// this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
 //#define LCD_FEEDBACK_FREQUENCY_DURATION_MS 100 // the duration the buzzer plays the UI feedback sound. ie Screen Click
-                                               // 0 to disable buzzer feedback  
+//#define LCD_FEEDBACK_FREQUENCY_HZ 1000         // this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
+                                                 // 0 to disable buzzer feedback. Test with M300 S<frequency Hz> P<duration ms>
 
 // PanelOne from T3P3 (via RAMPS 1.4 AUX2/AUX3)
 // http://reprap.org/wiki/PanelOne

Marlin/example_configurations/delta/kossel_mini/Configuration.h

 //#define ENCODER_STEPS_PER_MENU_ITEM 5 // Set according to ENCODER_PULSES_PER_STEP or your liking
 //#define ULTIMAKERCONTROLLER //as available from the Ultimaker online store.
 //#define ULTIPANEL  //the UltiPanel as on Thingiverse
-//#define LCD_FEEDBACK_FREQUENCY_HZ 1000	// this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
 //#define LCD_FEEDBACK_FREQUENCY_DURATION_MS 100 // the duration the buzzer plays the UI feedback sound. ie Screen Click
-                                               // 0 to disable buzzer feedback  
+//#define LCD_FEEDBACK_FREQUENCY_HZ 1000         // this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
+                                                 // 0 to disable buzzer feedback. Test with M300 S<frequency Hz> P<duration ms>
 
 // PanelOne from T3P3 (via RAMPS 1.4 AUX2/AUX3)
 // http://reprap.org/wiki/PanelOne

Marlin/example_configurations/makibox/Configuration.h

 //#define ENCODER_STEPS_PER_MENU_ITEM 5 // Set according to ENCODER_PULSES_PER_STEP or your liking
 //#define ULTIMAKERCONTROLLER //as available from the Ultimaker online store.
 //#define ULTIPANEL  //the UltiPanel as on Thingiverse
-//#define LCD_FEEDBACK_FREQUENCY_HZ 1000	// this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
 //#define LCD_FEEDBACK_FREQUENCY_DURATION_MS 100 // the duration the buzzer plays the UI feedback sound. ie Screen Click
-                                               // 0 to disable buzzer feedback  
+//#define LCD_FEEDBACK_FREQUENCY_HZ 1000         // this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
+                                                 // 0 to disable buzzer feedback. Test with M300 S<frequency Hz> P<duration ms>
 
 // PanelOne from T3P3 (via RAMPS 1.4 AUX2/AUX3)
 // http://reprap.org/wiki/PanelOne

Marlin/example_configurations/tvrrug/Round2/Configuration.h

 //#define ENCODER_STEPS_PER_MENU_ITEM 5 // Set according to ENCODER_PULSES_PER_STEP or your liking
 //#define ULTIMAKERCONTROLLER //as available from the Ultimaker online store.
 //#define ULTIPANEL  //the UltiPanel as on Thingiverse
-//#define LCD_FEEDBACK_FREQUENCY_HZ 1000	// this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
 //#define LCD_FEEDBACK_FREQUENCY_DURATION_MS 100 // the duration the buzzer plays the UI feedback sound. ie Screen Click
-                                               // 0 to disable buzzer feedback  
+//#define LCD_FEEDBACK_FREQUENCY_HZ 1000         // this is the tone frequency the buzzer plays when on UI feedback. ie Screen Click
+                                                 // 0 to disable buzzer feedback. Test with M300 S<frequency Hz> P<duration ms>
 
 // PanelOne from T3P3 (via RAMPS 1.4 AUX2/AUX3)
 // http://reprap.org/wiki/PanelOne

Marlin/ultralcd.cpp

     #endif    
     lcd_buzz(LCD_FEEDBACK_FREQUENCY_DURATION_MS, LCD_FEEDBACK_FREQUENCY_HZ);
   #elif defined(BEEPER) && BEEPER > -1
-    SET_OUTPUT(BEEPER);
     #ifndef LCD_FEEDBACK_FREQUENCY_HZ
       #define LCD_FEEDBACK_FREQUENCY_HZ 5000
     #endif
     #ifndef LCD_FEEDBACK_FREQUENCY_DURATION_MS
       #define LCD_FEEDBACK_FREQUENCY_DURATION_MS 2
     #endif
-    const uint16_t delay = 1000000 / LCD_FEEDBACK_FREQUENCY_HZ / 2;
-    uint16_t i = LCD_FEEDBACK_FREQUENCY_DURATION_MS * LCD_FEEDBACK_FREQUENCY_HZ / 1000;
-    while (i--) {
-      WRITE(BEEPER,HIGH);
-      delayMicroseconds(delay);
-      WRITE(BEEPER,LOW);
-      delayMicroseconds(delay);
-    }
-    const uint16_t j = max(10000 - LCD_FEEDBACK_FREQUENCY_DURATION_MS * 1000, 0);
-    if (j) delayMicroseconds(j);
+    lcd_buzz(LCD_FEEDBACK_FREQUENCY_DURATION_MS, LCD_FEEDBACK_FREQUENCY_HZ);
+  #else
+    #ifndef LCD_FEEDBACK_FREQUENCY_DURATION_MS
+      #define LCD_FEEDBACK_FREQUENCY_DURATION_MS 2
+    #endif
+    delay(LCD_FEEDBACK_FREQUENCY_DURATION_MS);
   #endif
 }
 
 }
 
 void lcd_buzz(long duration, uint16_t freq) {
-  #ifdef LCD_USE_I2C_BUZZER
-    lcd.buzz(duration,freq);
-  #endif
+  if (freq > 0) {
+    #if BEEPER > 0
+      SET_OUTPUT(BEEPER);
+      tone(BEEPER, freq);
+      delay(duration);
+      noTone(BEEPER);
+    #elif defined(LCD_USE_I2C_BUZZER)
+      lcd.buzz(duration,freq);
+    #else
+      delay(duration);
+    #endif
+  }
+  else {
+    delay(duration);
+  }
 }
 
 bool lcd_clicked() { return LCD_CLICKED; }