Added a feature to have filament change by gcode or display trigger.

[default off for now]
syntax: M600  X[pos] Y[pos] Z[relative lift] E[initial retract] L[later retract distance for removal]

if enabled, after a M600, the printer will retract by E, lift by Z, move to XY, retract even more filament.
Oh, and it will display "remove filament" and beep like crazy.

You are then supposed to insert a new filament (other color, e.g.) and click the display to continue.
After having the nozzle cleaned manually, aided by the disabled e-steppers.
After clicking, the printer will then go back the whole shebang, and continue printing with a fancy new color.

Marlin/Configuration_adv.h

 // #define FWRETRACT  //ONLY PARTIALLY TESTED
 #define MIN_RETRACT 0.1 //minimum extruded mm to accept a automatic gcode retraction attempt
 
+
+//adds support for experimental filament exchange support M600; requires display
+#ifdef ULTIPANEL
+  //#define FILAMENTCHANGEENABLE
+  #ifdef FILAMENTCHANGEENABLE
+    #define FILAMENTCHANGE_XPOS 3
+    #define FILAMENTCHANGE_YPOS 3
+    #define FILAMENTCHANGE_ZADD 10
+    #define FILAMENTCHANGE_FIRSTRETRACT -2
+    #define FILAMENTCHANGE_FINALRETRACT -100
+  #endif
+#endif
+ 
 //===========================================================================
 //=============================  Define Defines  ============================
 //===========================================================================

Marlin/Marlin_main.cpp

 // M502 - reverts to the default "factory settings".  You still need to store them in EEPROM afterwards if you want to.
 // M503 - print the current settings (from memory not from eeprom)
 // M540 - Use S[0|1] to enable or disable the stop SD card print on endstop hit (requires ABORT_ON_ENDSTOP_HIT_FEATURE_ENABLED)
+// M600 - Pause for filament change X[pos] Y[pos] Z[relative lift] E[initial retract] L[later retract distance for removal]
 // M907 - Set digital trimpot motor current using axis codes.
 // M908 - Control digital trimpot directly.
 // M350 - Set microstepping mode.
     }
     break;
     #endif
+    #ifdef FILAMENTCHANGEENABLE
+    case 600: //Pause for filament change X[pos] Y[pos] Z[relative lift] E[initial retract] L[later retract distance for removal]
+    {
+        float target[4];
+        float lastpos[4];
+        target[X_AXIS]=current_position[X_AXIS];
+        target[Y_AXIS]=current_position[Y_AXIS];
+        target[Z_AXIS]=current_position[Z_AXIS];
+        target[E_AXIS]=current_position[E_AXIS];
+        lastpos[X_AXIS]=current_position[X_AXIS];
+        lastpos[Y_AXIS]=current_position[Y_AXIS];
+        lastpos[Z_AXIS]=current_position[Z_AXIS];
+        lastpos[E_AXIS]=current_position[E_AXIS];
+        //retract by E
+        if(code_seen('E')) 
+        {
+          target[E_AXIS]+= code_value();
+        }
+        else
+        {
+          #ifdef FILAMENTCHANGE_FIRSTRETRACT
+            target[E_AXIS]+= FILAMENTCHANGE_FIRSTRETRACT ;
+          #endif
+        }
+        plan_buffer_line(target[X_AXIS], target[Y_AXIS], target[Z_AXIS], target[E_AXIS], feedrate/60, active_extruder);
+        
+        //lift Z
+        if(code_seen('Z')) 
+        {
+          target[Z_AXIS]+= code_value();
+        }
+        else
+        {
+          #ifdef FILAMENTCHANGE_ZADD
+            target[Z_AXIS]+= FILAMENTCHANGE_ZADD ;
+          #endif
+        }
+        plan_buffer_line(target[X_AXIS], target[Y_AXIS], target[Z_AXIS], target[E_AXIS], feedrate/60, active_extruder);
+        
+        //move xy
+        if(code_seen('X')) 
+        {
+          target[X_AXIS]+= code_value();
+        }
+        else
+        {
+          #ifdef FILAMENTCHANGE_XPOS
+            target[X_AXIS]= FILAMENTCHANGE_XPOS ;
+          #endif
+        }
+        if(code_seen('Y')) 
+        {
+          target[Y_AXIS]= code_value();
+        }
+        else
+        {
+          #ifdef FILAMENTCHANGE_YPOS
+            target[Y_AXIS]= FILAMENTCHANGE_YPOS ;
+          #endif
+        }
+        
+        plan_buffer_line(target[X_AXIS], target[Y_AXIS], target[Z_AXIS], target[E_AXIS], feedrate/60, active_extruder);
+        
+        if(code_seen('L'))
+        {
+          target[E_AXIS]+= code_value();
+        }
+        else
+        {
+          #ifdef FILAMENTCHANGE_FINALRETRACT
+            target[E_AXIS]+= FILAMENTCHANGE_FINALRETRACT ;
+          #endif
+        }
+        
+        plan_buffer_line(target[X_AXIS], target[Y_AXIS], target[Z_AXIS], target[E_AXIS], feedrate/60, active_extruder);
+        
+        //finish moves
+        st_synchronize();
+        //disable extruder steppers so filament can be removed
+        disable_e0();
+        disable_e1();
+        disable_e2();
+        delay(100);
+        LCD_ALERTMESSAGEPGM(MSG_FILAMENTCHANGE);
+        uint8_t cnt=0;
+        while(!LCD_CLICKED){
+          cnt++;
+          manage_heater();
+          manage_inactivity();
+          lcd_update();
+          
+          #if BEEPER > -1
+          if(cnt==0)
+          {
+            SET_OUTPUT(BEEPER);
+            
+            WRITE(BEEPER,HIGH);
+            delay(3);
+            WRITE(BEEPER,LOW);
+            delay(3);
+          }
+          #endif
+        }
+        
+        //return to normal
+        if(code_seen('L')) 
+        {
+          target[E_AXIS]+= -code_value();
+        }
+        else
+        {
+          #ifdef FILAMENTCHANGE_FINALRETRACT
+            target[E_AXIS]+=(-1)*FILAMENTCHANGE_FINALRETRACT ;
+          #endif
+        }
+        current_position[E_AXIS]=target[E_AXIS]; //the long retract of L is compensated by manual filament feeding
+        plan_set_e_position(current_position[E_AXIS]);
+        plan_buffer_line(target[X_AXIS], target[Y_AXIS], target[Z_AXIS], target[E_AXIS], feedrate/60, active_extruder); //should do nothing
+        plan_buffer_line(lastpos[X_AXIS], lastpos[Y_AXIS], target[Z_AXIS], target[E_AXIS], feedrate/60, active_extruder); //move xy back
+        plan_buffer_line(lastpos[X_AXIS], lastpos[Y_AXIS], lastpos[Z_AXIS], target[E_AXIS], feedrate/60, active_extruder); //move z back
+        plan_buffer_line(lastpos[X_AXIS], lastpos[Y_AXIS], lastpos[Z_AXIS], lastpos[E_AXIS], feedrate/60, active_extruder); //final untretract
+    }
+    break;
+    #endif //FILAMENTCHANGEENABLE    
     case 907: // M907 Set digital trimpot motor current using axis codes.
     {
       #if DIGIPOTSS_PIN > -1

Marlin/language.h

 	#define MSG_CONTROL_RETRACT_RECOVER "UnRet +mm"
 	#define MSG_CONTROL_RETRACT_RECOVERF "UnRet  F"
 	#define MSG_AUTORETRACT "AutoRetr."
+	#define MSG_FILAMENTCHANGE "Change filament"
 
 // Serial Console Messages
 
 	#define MSG_CONTROL_RETRACT_RECOVER "Cof. wycof. +mm"
 	#define MSG_CONTROL_RETRACT_RECOVERF "Cof. wycof.  F"
 	#define MSG_AUTORETRACT "Auto. wycofanie"
+	#define MSG_FILAMENTCHANGE "Change filament"
 
 // Serial Console Messages
 
 #define MSG_CONTROL_RETRACT_RECOVER " UnRet +mm:"
 #define MSG_CONTROL_RETRACT_RECOVERF " UnRet F:"
 #define MSG_AUTORETRACT " Retract. Auto.:"
+#define MSG_FILAMENTCHANGE "Change filament"
 
 // Serial Console Messages
 
     #define MSG_CONTROL_RETRACT_RECOVER "UnRet +mm"
     #define MSG_CONTROL_RETRACT_RECOVERF "UnRet  F"
     #define MSG_AUTORETRACT      "AutoRetr."
+    #define MSG_FILAMENTCHANGE "Filament wechseln"
 	
 // Serial Console Messages
 
 #define MSG_CONTROL_RETRACT_RECOVER " DesRet +mm:"
 #define MSG_CONTROL_RETRACT_RECOVERF " DesRet F:"
 #define MSG_AUTORETRACT " AutoRetr.:"
-
+#define MSG_FILAMENTCHANGE "Change filament"
 // Serial Console Messages
 
 #define MSG_Enqueing "En cola \""
 #define MSG_CONTROL_RETRACT_RECOVER			" Возврат +mm:"
 #define MSG_CONTROL_RETRACT_RECOVERF		" Возврат  F:"
 #define MSG_AUTORETRACT						" АвтоОткат:"
+#define MSG_FILAMENTCHANGE "Change filament"
 
 // Serial Console Messages
 
 	#define MSG_CONTROL_RETRACT_RECOVERF " UnRet  F:"
 	#define MSG_AUTORETRACT          " AutoRilascio.:"
 	#define MSG_SERIAL_ERROR_MENU_STRUCTURE "Qualcosa non va in MenuStructure."
+	#define MSG_FILAMENTCHANGE "Change filament"
 
 	// Serial Console Messages
 
 	#define MSG_CONTROL_RETRACT_RECOVERF " DesRet  F:"
 	#define MSG_AUTORETRACT " AutoRetr.:"
         #define MSG_SERIAL_ERROR_MENU_STRUCTURE "Algo esta errado na estrutura do Menu."
+        #define MSG_FILAMENTCHANGE "Change filament"
 
 // Serial Console Messages
 
 	#define MSG_CONTROL_RETRACT_RECOVER "UnRet +mm"
 	#define MSG_CONTROL_RETRACT_RECOVERF "UnRet  F"
 	#define MSG_AUTORETRACT "AutoVeto."
+	#define MSG_FILAMENTCHANGE "Change filament"
 
 // Serial Console Messages
 

Marlin/ultralcd.cpp

 #endif
     MENU_ITEM_EDIT(int3, MSG_FAN_SPEED, &fanSpeed, 0, 255);
     MENU_ITEM_EDIT(int3, MSG_FLOW, &extrudemultiply, 10, 999);
+#ifdef FILAMENTCHANGEENABLE
+     MENU_ITEM(gcode, MSG_FILAMENTCHANGE, PSTR("M600"));
+#endif
     END_MENU();
 }