* Auto filament change on CHANGEFILAMENT feature. Now you can activate this option that extrude filament until you press the button.

Marlin/Configuration_adv.h

@@ -446,6 +446,9 @@ const unsigned int dropsegments=5; //everything with less than this number of st
     #define FILAMENTCHANGE_ZADD 10
     #define FILAMENTCHANGE_FIRSTRETRACT -2
     #define FILAMENTCHANGE_FINALRETRACT -100
+    #define AUTO_FILAMENT_CHANGE                //This extrude filament until you press the button on LCD
+    #define AUTO_FILAMENT_CHANGE_LENGTH 0.04    //Extrusion length on automatic extrusion loop
+    #define AUTO_FILAMENT_CHANGE_FEEDRATE 300   //Extrusion feedrate (mm/min) on automatic extrusion loop
   #endif
 #endif
 

Marlin/Marlin_main.cpp

@@ -4958,12 +4958,23 @@ inline void gcode_M503() {
     LCD_ALERTMESSAGEPGM(MSG_FILAMENTCHANGE);
     uint8_t cnt = 0;
     while (!lcd_clicked()) {
-      if (++cnt == 0) lcd_quick_feedback(); // every 256th frame till the lcd is clicked
-      manage_heater();
-      manage_inactivity(true);
-      lcd_update();
+      #ifndef AUTO_FILAMENT_CHANGE
+        if (++cnt == 0) lcd_quick_feedback(); // every 256th frame till the lcd is clicked
+        manage_heater();
+        manage_inactivity(true);
+        lcd_update();
+      #else
+        current_position[E_AXIS] += AUTO_FILAMENT_CHANGE_LENGTH;
+        plan_buffer_line(target[X_AXIS],target[Y_AXIS],target[Z_MAX_ENDSTOP_INVERTING],current_position[E_AXIS],AUTO_FILAMENT_CHANGE_FEEDRATE/60,active_extruder);
+        st_synchronize();
+      #endif
     } // while(!lcd_clicked)
 
+    #ifdef AUTO_FILAMENT_CHANGE
+      current_position[E_AXIS]= 0;
+      st_synchronize();
+    #endif
+          
     //return to normal
     if (code_seen('L')) target[E_AXIS] -= code_value();
     #ifdef FILAMENTCHANGE_FINALRETRACT