prevent too long extrudes, or too cold extrudes

Marlin/Configuration.h

 // if unwanted behavior is observed on a user's machine when running at very slow speeds.
 #define MINIMUM_PLANNER_SPEED 2.0 // (mm/sec)
 
-// If defined the movements slow down when the look ahead buffer is only half full
-#define SLOWDOWN
-
 // BASIC SETTINGS: select your board type, thermistor type, axis scaling, and endstop configuration
 
 //// The following define selects which electronics board you have. Please choose the one that matches your setup
 #define DEFAULT_XYJERK                20.0    // (mm/sec)
 #define DEFAULT_ZJERK                 0.4     // (mm/sec)
 
+// If defined the movements slow down when the look ahead buffer is only half full
+#define SLOWDOWN
 
+//default stepper release if idle
+#define DEFAULT_STEPPER_DEACTIVE_TIME 60
+#define DEFAULT_STEPPER_DEACTIVE_COMMAND "M84 X Y E"  //z stays  powered
 
 
 //===========================================================================
   #define AUTOTEMP_OLDWEIGHT 0.98
 #endif
 
+//this prevents dangerous Extruder moves, i.e. if the temperature is under the limit
+//can be software-disabled for whatever purposes by
+#define PREVENT_DANGEROUS_EXTRUDE
+#define EXTRUDE_MINTEMP 190
+#define EXTRUDE_MAXLENGTH (X_MAX_LENGTH+Y_MAX_LENGTH) //prevent extrusion of very large distances.
 
 const int dropsegments=5; //everything with less than this number of steps will be ignored as move and joined with the next movement
 

Marlin/Marlin.pde

 // M206 - set additional homeing offset
 // M220 - set speed factor override percentage S:factor in percent
 // M301 - Set PID parameters P I and D
+// M302 - Allow cold extrudes
 // M400 - Finish all moves
 // M500 - stores paramters in EEPROM
 // M501 - reads parameters from EEPROM (if you need reset them after you changed them temporarily).  
 //Inactivity shutdown variables
 static unsigned long previous_millis_cmd = 0;
 static unsigned long max_inactive_time = 0;
-static unsigned long stepper_inactive_time = 0;
+static unsigned long stepper_inactive_time = DEFAULT_STEPPER_DEACTIVE_TIME*1000;
+static unsigned long last_stepperdisabled_time=30*1000; //first release check after 30 seconds
 
 static unsigned long starttime=0;
 static unsigned long stoptime=0;
       }
       break;
     #endif //PIDTEMP
+      
+    case 302: // finish all moves
+    {
+      allow_cold_extrudes(true);
+    }
+    break;
     case 400: // finish all moves
     {
       st_synchronize();
   if( (millis()-previous_millis_cmd) >  max_inactive_time ) 
     if(max_inactive_time) 
       kill(); 
-  if( (millis()-previous_millis_cmd) >  stepper_inactive_time ) 
-    if(stepper_inactive_time) 
-    { 
-      disable_x(); 
-      disable_y(); 
-      disable_z(); 
-      disable_e(); 
+  if(stepper_inactive_time)  
+  if( (millis()-last_stepperdisabled_time) >  stepper_inactive_time ) 
+  {
+    if(previous_millis_cmd>last_stepperdisabled_time)
+      last_stepperdisabled_time=previous_millis_cmd;
+    else
+    {
+      enquecommand(DEFAULT_STEPPER_DEACTIVE_COMMAND); 
+      last_stepperdisabled_time=millis();
     }
+  }
   #ifdef EXTRUDER_RUNOUT_PREVENT
     if( (millis()-previous_millis_cmd) >  EXTRUDER_RUNOUT_SECONDS*1000 ) 
     if(degHotend(active_extruder)>EXTRUDER_RUNOUT_MINTEMP)

Marlin/planner.cpp

 //===========================================================================
 //=============================private variables ============================
 //===========================================================================
-
+#ifdef PREVENT_DANGEROUS_EXTRUDE
+  bool allow_cold_extrude=false;
+#endif
 #ifdef XY_FREQUENCY_LIMIT
   // Used for the frequency limit
   static unsigned char old_direction_bits = 0;               // Old direction bits. Used for speed calculations
   target[X_AXIS] = lround(x*axis_steps_per_unit[X_AXIS]);
   target[Y_AXIS] = lround(y*axis_steps_per_unit[Y_AXIS]);
   target[Z_AXIS] = lround(z*axis_steps_per_unit[Z_AXIS]);     
-  target[E_AXIS] = lround(e*axis_steps_per_unit[E_AXIS]); 
+  target[E_AXIS] = lround(e*axis_steps_per_unit[E_AXIS]);
+  
+  #ifdef PREVENT_DANGEROUS_EXTRUDE
+    if(target[E_AXIS]!=position[E_AXIS])
+    if(degHotend(active_extruder)<EXTRUDE_MINTEMP && !allow_cold_extrude)
+    {
+      position[E_AXIS]=target[E_AXIS]; //behave as if the move really took place, but ignore E part
+      SERIAL_ECHO_START;
+      SERIAL_ECHOLNPGM(" cold extrusion prevented");
+    }
+    if(labs(target[E_AXIS]-position[E_AXIS])>axis_steps_per_unit[E_AXIS]*EXTRUDE_MAXLENGTH)
+    {
+      position[E_AXIS]=target[E_AXIS]; //behave as if the move really took place, but ignore E part
+      SERIAL_ECHO_START;
+      SERIAL_ECHOLNPGM(" too long extrusion prevented");
+    }
+  #endif
   
   // Prepare to set up new block
   block_t *block = &block_buffer[block_buffer_head];
  return (block_buffer_head-block_buffer_tail + BLOCK_BUFFER_SIZE) & (BLOCK_BUFFER_SIZE - 1);
 }
 
+void allow_cold_extrudes(bool allow)
+{
+  #ifdef PREVENT_DANGEROUS_EXTRUDE
+    allow_cold_extrude=allow;
+  #endif
+}

Marlin/planner.h

   else
     return true;
 }
+
+void allow_cold_extrudes(bool allow);
 #endif