Ported over Johann Rocholl's improvements for delta printers:

- Nonlinear auto bed leveling code (includes G29, G30, Z_RAISE_AFTER_PROBING). Cleaned it up to be a delta-specific AUTO_BED_LEVELING_GRID code path.
- Allen key z-probe deployment and retraction code. Cleaned it up and added safety checks.

Marlin/Marlin.h

 void get_coordinates();
 #ifdef DELTA
 void calculate_delta(float cartesian[3]);
+  #ifdef ENABLE_AUTO_BED_LEVELING
+  extern int delta_grid_spacing[2];
+  void adjust_delta(float cartesian[3]);
+  #endif
 extern float delta[3];
+void prepare_move_raw();
 #endif
 #ifdef SCARA
 void calculate_delta(float cartesian[3]);
 void calculate_SCARA_forward_Transform(float f_scara[3]);
 #endif
+void reset_bed_level();
 void prepare_move();
 void kill();
 void Stop();

Marlin/Marlin_main.cpp

   float delta_diagonal_rod = DELTA_DIAGONAL_ROD;
   float delta_diagonal_rod_2 = sq(delta_diagonal_rod);
   float delta_segments_per_second = DELTA_SEGMENTS_PER_SECOND;
+  #ifdef ENABLE_AUTO_BED_LEVELING
+    float bed_level[AUTO_BED_LEVELING_GRID_POINTS][AUTO_BED_LEVELING_GRID_POINTS];
+  #endif
 #endif
 
 #ifdef SCARA
 
 #ifdef ENABLE_AUTO_BED_LEVELING
 #ifdef AUTO_BED_LEVELING_GRID
+
+#ifndef DELTA
 static void set_bed_level_equation_lsq(double *plane_equation_coefficients)
 {
     vector_3 planeNormal = vector_3(-plane_equation_coefficients[0], -plane_equation_coefficients[1], 1);
 
     plan_set_position(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS]);
 }
+#endif
 
 #else // not AUTO_BED_LEVELING_GRID
 
 #endif // AUTO_BED_LEVELING_GRID
 
 static void run_z_probe() {
+  #ifdef DELTA
+    
+    float start_z = current_position[Z_AXIS];
+    long start_steps = st_get_position(Z_AXIS);
+  
+    // move down slowly until you find the bed
+    feedrate = homing_feedrate[Z_AXIS] / 4;
+    destination[Z_AXIS] = -10;
+    prepare_move_raw();
+    st_synchronize();
+    endstops_hit_on_purpose();
+    
+    // we have to let the planner know where we are right now as it is not where we said to go.
+    long stop_steps = st_get_position(Z_AXIS);
+    float mm = start_z - float(start_steps - stop_steps) / axis_steps_per_unit[Z_AXIS];
+    current_position[Z_AXIS] = mm;
+    calculate_delta(current_position);
+    plan_set_position(delta[X_AXIS], delta[Y_AXIS], delta[Z_AXIS], current_position[E_AXIS]);
+    
+  #else
+
     plan_bed_level_matrix.set_to_identity();
     feedrate = homing_feedrate[Z_AXIS];
 
     current_position[Z_AXIS] = st_get_position_mm(Z_AXIS);
     // make sure the planner knows where we are as it may be a bit different than we last said to move to
     plan_set_position(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS]);
+    
+  #endif
 }
 
 static void do_blocking_move_to(float x, float y, float z) {
     float oldFeedRate = feedrate;
 
+#ifdef DELTA
+
+    feedrate = XY_TRAVEL_SPEED;
+    
+    destination[X_AXIS] = x;
+    destination[Y_AXIS] = y;
+    destination[Z_AXIS] = z;
+    prepare_move_raw();
+    st_synchronize();
+
+#else
+
     feedrate = homing_feedrate[Z_AXIS];
 
     current_position[Z_AXIS] = z;
     plan_buffer_line(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS], feedrate/60, active_extruder);
     st_synchronize();
 
+#endif
+
     feedrate = oldFeedRate;
 }
 
         servos[servo_endstops[Z_AXIS]].detach();
       #endif
     }
+  #elif defined(Z_PROBE_ALLEN_KEY)
+    feedrate = homing_feedrate[X_AXIS];
+    
+    // Move to the start position to initiate deployment
+    destination[X_AXIS] = Z_PROBE_ALLEN_KEY_DEPLOY_X;
+    destination[Y_AXIS] = Z_PROBE_ALLEN_KEY_DEPLOY_Y;
+    destination[Z_AXIS] = Z_PROBE_ALLEN_KEY_DEPLOY_Z;
+    prepare_move_raw();
+
+    // Home X to touch the belt
+    feedrate = homing_feedrate[X_AXIS]/10;
+    destination[X_AXIS] = 0;
+    prepare_move_raw();
+    
+    // Home Y for safety
+    feedrate = homing_feedrate[X_AXIS]/2;
+    destination[Y_AXIS] = 0;
+    prepare_move_raw();
+    
+    st_synchronize();
+    
+    bool z_min_endstop = (READ(Z_MIN_PIN) != Z_MIN_ENDSTOP_INVERTING);
+    if (z_min_endstop)
+    {
+        if (!Stopped)
+        {
+            SERIAL_ERROR_START;
+            SERIAL_ERRORLNPGM("Z-Probe failed to engage!");
+            LCD_ALERTMESSAGEPGM("Err: ZPROBE");
+        }
+        Stop();
+    }
   #endif
+
 }
 
 static void retract_z_probe() {
         servos[servo_endstops[Z_AXIS]].detach();
       #endif
     }
+  #elif defined(Z_PROBE_ALLEN_KEY)
+    // Move up for safety
+    feedrate = homing_feedrate[X_AXIS];
+    destination[Z_AXIS] = current_position[Z_AXIS] + 20;
+    prepare_move_raw();
+
+    // Move to the start position to initiate retraction
+    destination[X_AXIS] = Z_PROBE_ALLEN_KEY_RETRACT_X;
+    destination[Y_AXIS] = Z_PROBE_ALLEN_KEY_RETRACT_Y;
+    destination[Z_AXIS] = Z_PROBE_ALLEN_KEY_RETRACT_Z;
+    prepare_move_raw();
+
+    // Move the nozzle down to push the probe into retracted position
+    feedrate = homing_feedrate[Z_AXIS]/10;
+    destination[Z_AXIS] = current_position[Z_AXIS] - Z_PROBE_ALLEN_KEY_RETRACT_DEPTH;
+    prepare_move_raw();
+    
+    // Move up for safety
+    feedrate = homing_feedrate[Z_AXIS]/2;
+    destination[Z_AXIS] = current_position[Z_AXIS] + Z_PROBE_ALLEN_KEY_RETRACT_DEPTH * 2;
+    prepare_move_raw();
+    
+    // Home XY for safety
+    feedrate = homing_feedrate[X_AXIS]/2;
+    destination[X_AXIS] = 0;
+    destination[Y_AXIS] = 0;
+    prepare_move_raw();
+    
+    st_synchronize();
+    
+    bool z_min_endstop = (READ(Z_MIN_PIN) != Z_MIN_ENDSTOP_INVERTING);
+    if (!z_min_endstop)
+    {
+        if (!Stopped)
+        {
+            SERIAL_ERROR_START;
+            SERIAL_ERRORLNPGM("Z-Probe failed to retract!");
+            LCD_ALERTMESSAGEPGM("Err: ZPROBE");
+        }
+        Stop();
+    }
   #endif
+
 }
 
 enum ProbeAction { ProbeStay, ProbeEngage, ProbeRetract, ProbeEngageRetract };
   do_blocking_move_to(current_position[X_AXIS], current_position[Y_AXIS], z_before);
   do_blocking_move_to(x - X_PROBE_OFFSET_FROM_EXTRUDER, y - Y_PROBE_OFFSET_FROM_EXTRUDER, current_position[Z_AXIS]);
 
-  #ifndef Z_PROBE_SLED
+  #if !defined(Z_PROBE_SLED) && !defined(Z_PROBE_ALLEN_KEY)
     if (retract_action & ProbeEngage) engage_z_probe();
   #endif
 
   run_z_probe();
   float measured_z = current_position[Z_AXIS];
 
-  #ifndef Z_PROBE_SLED
+  #if !defined(Z_PROBE_SLED) && !defined(Z_PROBE_ALLEN_KEY)
     if (retract_action & ProbeRetract) retract_z_probe();
   #endif
 
   return measured_z;
 }
 
+#ifdef DELTA
+static void extrapolate_one_point(int x, int y, int xdir, int ydir) {
+  if (bed_level[x][y] != 0.0) {
+    return;  // Don't overwrite good values.
+  }
+  float a = 2*bed_level[x+xdir][y] - bed_level[x+xdir*2][y];  // Left to right.
+  float b = 2*bed_level[x][y+ydir] - bed_level[x][y+ydir*2];  // Front to back.
+  float c = 2*bed_level[x+xdir][y+ydir] - bed_level[x+xdir*2][y+ydir*2];  // Diagonal.
+  float median = c;  // Median is robust (ignores outliers).
+  if (a < b) {
+    if (b < c) median = b;
+    if (c < a) median = a;
+  } else {  // b <= a
+    if (c < b) median = b;
+    if (a < c) median = a;
+  }
+  bed_level[x][y] = median;
+}
+
+// Fill in the unprobed points (corners of circular print surface)
+// using linear extrapolation, away from the center.
+static void extrapolate_unprobed_bed_level() {
+  int half = (AUTO_BED_LEVELING_GRID_POINTS-1)/2;
+  for (int y = 0; y <= half; y++) {
+    for (int x = 0; x <= half; x++) {
+      if (x + y < 3) continue;
+      extrapolate_one_point(half-x, half-y, x>1?+1:0, y>1?+1:0);
+      extrapolate_one_point(half+x, half-y, x>1?-1:0, y>1?+1:0);
+      extrapolate_one_point(half-x, half+y, x>1?+1:0, y>1?-1:0);
+      extrapolate_one_point(half+x, half+y, x>1?-1:0, y>1?-1:0);
+    }
+  }
+}
+
+// Print calibration results for plotting or manual frame adjustment.
+static void print_bed_level() {
+  for (int y = 0; y < AUTO_BED_LEVELING_GRID_POINTS; y++) {
+    for (int x = 0; x < AUTO_BED_LEVELING_GRID_POINTS; x++) {
+      SERIAL_PROTOCOL_F(bed_level[x][y], 2);
+      SERIAL_PROTOCOLPGM(" ");
+    }
+    SERIAL_ECHOLN("");
+  }
+}
+
+// Reset calibration results to zero.
+void reset_bed_level() {
+  for (int y = 0; y < AUTO_BED_LEVELING_GRID_POINTS; y++) {
+    for (int x = 0; x < AUTO_BED_LEVELING_GRID_POINTS; x++) {
+      bed_level[x][y] = 0.0;
+    }
+  }
+}
+
+#endif // DELTA
+
 #endif // ENABLE_AUTO_BED_LEVELING
 
 static void homeaxis(int axis) {
  */
 inline void gcode_G28() {
   #ifdef ENABLE_AUTO_BED_LEVELING
-    plan_bed_level_matrix.set_to_identity();  //Reset the plane ("erase" all leveling data)
+    #ifdef DELTA
+      reset_bed_level();
+    #else
+      plan_bed_level_matrix.set_to_identity();  //Reset the plane ("erase" all leveling data)
+    #endif
   #endif
 
   saved_feedrate = feedrate;
    * Parameters With AUTO_BED_LEVELING_GRID:
    *
    *  P  Set the size of the grid that will be probed (P x P points).
+   *     Not supported by non-linear delta printer bed leveling.
    *     Example: "G29 P4"
    *
    *  V  Set the verbose level (0-4). Example: "G29 V3"
    *  T  Generate a Bed Topology Report. Example: "G29 P5 T" for a detailed report.
    *     This is useful for manual bed leveling and finding flaws in the bed (to
    *     assist with part placement).
+   *     Not supported by non-linear delta printer bed leveling.
    *
    *  F  Set the Front limit of the probing grid
    *  B  Set the Back limit of the probing grid
 
     #ifdef AUTO_BED_LEVELING_GRID
 
+    #ifndef DELTA
       bool topo_flag = verbose_level > 2 || code_seen('T') || code_seen('t');
+    #endif
 
       if (verbose_level > 0)
         SERIAL_PROTOCOLPGM("G29 Auto Bed Leveling\n");
 
-      int auto_bed_leveling_grid_points = code_seen('P') ? code_value_long() : AUTO_BED_LEVELING_GRID_POINTS;
-      if (auto_bed_leveling_grid_points < 2 || auto_bed_leveling_grid_points > AUTO_BED_LEVELING_GRID_POINTS) {
-        SERIAL_PROTOCOLPGM("?Number of probed (P)oints is implausible (2 minimum).\n");
-        return;
-      }
+      int auto_bed_leveling_grid_points = AUTO_BED_LEVELING_GRID_POINTS;
+      #ifndef DELTA
+        if (code_seen('P')) auto_bed_leveling_grid_points = code_value_long();
+        if (auto_bed_leveling_grid_points < 2 || auto_bed_leveling_grid_points > AUTO_BED_LEVELING_GRID_POINTS) {
+          SERIAL_PROTOCOLPGM("?Number of probed (P)oints is implausible (2 minimum).\n");
+          return;
+        }
+      #endif
 
       int left_probe_bed_position = code_seen('L') ? code_value_long() : LEFT_PROBE_BED_POSITION,
           right_probe_bed_position = code_seen('R') ? code_value_long() : RIGHT_PROBE_BED_POSITION,
 
     #ifdef Z_PROBE_SLED
       dock_sled(false); // engage (un-dock) the probe
+    #elif not defined(SERVO_ENDSTOPS)
+      engage_z_probe();
     #endif
 
     st_synchronize();
 
+  #ifdef DELTA
+    reset_bed_level();
+  #else
     // make sure the bed_level_rotation_matrix is identity or the planner will get it incorectly
     //vector_3 corrected_position = plan_get_position_mm();
     //corrected_position.debug("position before G29");
     plan_bed_level_matrix.set_to_identity();
     vector_3 uncorrected_position = plan_get_position();
-    //uncorrected_position.debug("position durring G29");
+    //uncorrected_position.debug("position during G29");
     current_position[X_AXIS] = uncorrected_position.x;
     current_position[Y_AXIS] = uncorrected_position.y;
     current_position[Z_AXIS] = uncorrected_position.z;
     plan_set_position(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS]);
+  #endif
+
     setup_for_endstop_move();
 
     feedrate = homing_feedrate[Z_AXIS];
     #ifdef AUTO_BED_LEVELING_GRID
 
       // probe at the points of a lattice grid
-      int xGridSpacing = (right_probe_bed_position - left_probe_bed_position) / (auto_bed_leveling_grid_points - 1);
-      int yGridSpacing = (back_probe_bed_position - front_probe_bed_position) / (auto_bed_leveling_grid_points - 1);
+      const int xGridSpacing = (right_probe_bed_position - left_probe_bed_position) / (auto_bed_leveling_grid_points-1);
+      const int yGridSpacing = (back_probe_bed_position - front_probe_bed_position) / (auto_bed_leveling_grid_points-1);
 
+    #ifndef DELTA
       // solve the plane equation ax + by + d = z
       // A is the matrix with rows [x y 1] for all the probed points
       // B is the vector of the Z positions
              eqnBVector[abl2],     // "B" vector of Z points
              mean = 0.0;
 
+    #else
+      delta_grid_spacing[0] = xGridSpacing;
+      delta_grid_spacing[1] = yGridSpacing;
+
+      float z_offset = Z_PROBE_OFFSET_FROM_EXTRUDER;
+      if (code_seen(axis_codes[Z_AXIS])) {
+        z_offset += code_value();
+      }
+    #endif
+
       int probePointCounter = 0;
       bool zig = true;
 
-      for (int yProbe = front_probe_bed_position; yProbe <= back_probe_bed_position; yProbe += yGridSpacing) {
-        int xProbe, xInc;
+      for (int yCount=0; yCount < auto_bed_leveling_grid_points; yCount++)
+      {
+        double yProbe = front_probe_bed_position + yGridSpacing * yCount;
+        int xStart, xStop, xInc;
 
         if (zig)
-          xProbe = left_probe_bed_position, xInc = xGridSpacing;
+        {
+          xStart = 0;
+          xStop = auto_bed_leveling_grid_points;
+          xInc = 1;
+          zig = false;
+        }
         else
-          xProbe = right_probe_bed_position, xInc = -xGridSpacing;
+        {
+          xStart = auto_bed_leveling_grid_points - 1;
+          xStop = -1;
+          xInc = -1;
+          zig = true;
+        }
 
+      #ifndef DELTA
         // If topo_flag is set then don't zig-zag. Just scan in one direction.
         // This gets the probe points in more readable order.
         if (!topo_flag) zig = !zig;
+      #endif
+
+        for (int xCount=xStart; xCount != xStop; xCount += xInc)
+        {
+          double xProbe = left_probe_bed_position + xGridSpacing * xCount;
 
-        for (int xCount = 0; xCount < auto_bed_leveling_grid_points; xCount++) {
           // raise extruder
           float measured_z,
                 z_before = probePointCounter == 0 ? Z_RAISE_BEFORE_PROBING : current_position[Z_AXIS] + Z_RAISE_BETWEEN_PROBINGS;
 
+        #ifdef DELTA
+          // Avoid probing the corners (outside the round or hexagon print surface) on a delta printer.
+          float distance_from_center = sqrt(xProbe*xProbe + yProbe*yProbe);
+          if (distance_from_center > DELTA_PROBABLE_RADIUS)
+            continue;
+        #endif //DELTA
+
           // Enhanced G29 - Do not retract servo between probes
           ProbeAction act;
           if (enhanced_g29) {
 
           measured_z = probe_pt(xProbe, yProbe, z_before, act, verbose_level);
 
+        #ifndef DELTA
           mean += measured_z;
 
           eqnBVector[probePointCounter] = measured_z;
           eqnAMatrix[probePointCounter + 0 * abl2] = xProbe;
           eqnAMatrix[probePointCounter + 1 * abl2] = yProbe;
           eqnAMatrix[probePointCounter + 2 * abl2] = 1;
+        #else
+          bed_level[xCount][yCount] = measured_z + z_offset;
+        #endif
 
           probePointCounter++;
-          xProbe += xInc;
-
         } //xProbe
-
       } //yProbe
 
       clean_up_after_endstop_move();
 
+    #ifndef DELTA
       // solve lsq problem
       double *plane_equation_coefficients = qr_solve(abl2, 3, eqnAMatrix, eqnBVector);
 
 
       set_bed_level_equation_lsq(plane_equation_coefficients);
       free(plane_equation_coefficients);
+    #else
+      extrapolate_unprobed_bed_level();
+      print_bed_level();
+    #endif
 
     #else // !AUTO_BED_LEVELING_GRID
 
 
     #endif // !AUTO_BED_LEVELING_GRID
 
+    do_blocking_move_to(MANUAL_X_HOME_POS, MANUAL_Y_HOME_POS, Z_RAISE_AFTER_PROBING);
     st_synchronize();
 
     if (verbose_level > 0)
       plan_bed_level_matrix.debug(" \n\nBed Level Correction Matrix:");
 
+  #ifndef DELTA
     // Correct the Z height difference from z-probe position and hotend tip position.
     // The Z height on homing is measured by Z-Probe, but the probe is quite far from the hotend.
     // When the bed is uneven, this height must be corrected.
     apply_rotation_xyz(plan_bed_level_matrix, x_tmp, y_tmp, z_tmp);         //Apply the correction sending the probe offset
     current_position[Z_AXIS] = z_tmp - real_z + current_position[Z_AXIS];   //The difference is added to current position and sent to planner.
     plan_set_position(current_position[X_AXIS], current_position[Y_AXIS], current_position[Z_AXIS], current_position[E_AXIS]);
+  #endif
 
-    #ifdef Z_PROBE_SLED
-      dock_sled(true, -SLED_DOCKING_OFFSET); // dock the probe, correcting for over-travel
-    #endif
+  #ifdef Z_PROBE_SLED
+    dock_sled(true, -SLED_DOCKING_OFFSET); // dock the probe, correcting for over-travel
+  #elif not defined(SERVO_ENDSTOPS)
+    retract_z_probe();
+  #endif
   }
 
   #ifndef Z_PROBE_SLED
   SERIAL_ECHOPGM(" z="); SERIAL_ECHOLN(delta[Z_AXIS]);
   */
 }
-#endif
+
+#ifdef ENABLE_AUTO_BED_LEVELING
+// Adjust print surface height by linear interpolation over the bed_level array.
+int delta_grid_spacing[2] = { 0, 0 };
+void adjust_delta(float cartesian[3])
+{
+  if (delta_grid_spacing[0] == 0 || delta_grid_spacing[1] == 0)
+    return; // G29 not done
+
+  int half = (AUTO_BED_LEVELING_GRID_POINTS - 1) / 2;
+  float grid_x = max(0.001-half, min(half-0.001, cartesian[X_AXIS] / delta_grid_spacing[0]));
+  float grid_y = max(0.001-half, min(half-0.001, cartesian[Y_AXIS] / delta_grid_spacing[1]));
+  int floor_x = floor(grid_x);
+  int floor_y = floor(grid_y);
+  float ratio_x = grid_x - floor_x;
+  float ratio_y = grid_y - floor_y;
+  float z1 = bed_level[floor_x+half][floor_y+half];
+  float z2 = bed_level[floor_x+half][floor_y+half+1];
+  float z3 = bed_level[floor_x+half+1][floor_y+half];
+  float z4 = bed_level[floor_x+half+1][floor_y+half+1];
+  float left = (1-ratio_y)*z1 + ratio_y*z2;
+  float right = (1-ratio_y)*z3 + ratio_y*z4;
+  float offset = (1-ratio_x)*left + ratio_x*right;
+
+  delta[X_AXIS] += offset;
+  delta[Y_AXIS] += offset;
+  delta[Z_AXIS] += offset;
+
+  /*
+  SERIAL_ECHOPGM("grid_x="); SERIAL_ECHO(grid_x);
+  SERIAL_ECHOPGM(" grid_y="); SERIAL_ECHO(grid_y);
+  SERIAL_ECHOPGM(" floor_x="); SERIAL_ECHO(floor_x);
+  SERIAL_ECHOPGM(" floor_y="); SERIAL_ECHO(floor_y);
+  SERIAL_ECHOPGM(" ratio_x="); SERIAL_ECHO(ratio_x);
+  SERIAL_ECHOPGM(" ratio_y="); SERIAL_ECHO(ratio_y);
+  SERIAL_ECHOPGM(" z1="); SERIAL_ECHO(z1);
+  SERIAL_ECHOPGM(" z2="); SERIAL_ECHO(z2);
+  SERIAL_ECHOPGM(" z3="); SERIAL_ECHO(z3);
+  SERIAL_ECHOPGM(" z4="); SERIAL_ECHO(z4);
+  SERIAL_ECHOPGM(" left="); SERIAL_ECHO(left);
+  SERIAL_ECHOPGM(" right="); SERIAL_ECHO(right);
+  SERIAL_ECHOPGM(" offset="); SERIAL_ECHOLN(offset);
+  */
+}
+#endif //ENABLE_AUTO_BED_LEVELING
+
+void prepare_move_raw()
+{
+  previous_millis_cmd = millis();
+  calculate_delta(destination);
+  plan_buffer_line(delta[X_AXIS], delta[Y_AXIS], delta[Z_AXIS],
+                   destination[E_AXIS], feedrate*feedmultiply/60/100.0,
+                   active_extruder);
+  for(int8_t i=0; i < NUM_AXIS; i++) {
+    current_position[i] = destination[i];
+  }
+}
+#endif //DELTA
 
 void prepare_move()
 {

Marlin/example_configurations/delta/Configuration.h

 // Effective horizontal distance bridged by diagonal push rods.
 #define DELTA_RADIUS (DELTA_SMOOTH_ROD_OFFSET-DELTA_EFFECTOR_OFFSET-DELTA_CARRIAGE_OFFSET)
 
+// Print surface diameter/2 minus unreachable space (avoid collisions with vertical towers).
+#define DELTA_PRINTABLE_RADIUS 90
+
 
 //===========================================================================
 //============================= Thermal Settings ============================
 const bool Y_MAX_ENDSTOP_INVERTING = true; // set to true to invert the logic of the endstop.
 const bool Z_MAX_ENDSTOP_INVERTING = true; // set to true to invert the logic of the endstop.
 //#define DISABLE_MAX_ENDSTOPS
-// Deltas never have min endstops
-#define DISABLE_MIN_ENDSTOPS
+#define DISABLE_MIN_ENDSTOPS // Deltas only use min endstops for probing
 
 // For Inverting Stepper Enable Pins (Active Low) use 0, Non Inverting (Active High) use 1
 #define X_ENABLE_ON 0
 //============================= Bed Auto Leveling ===========================
 //===========================================================================
 
-//Bed Auto Leveling is still not compatible with Delta Kinematics
+//#define ENABLE_AUTO_BED_LEVELING // Delete the comment to enable (remove // at the start of the line)
+// Z-Probe Repeatability test is not supported in Deltas yet.
+
+#ifdef ENABLE_AUTO_BED_LEVELING
+
+  // Deltas only support grid mode
+  #define AUTO_BED_LEVELING_GRID
+
+  #define DELTA_PROBABLE_RADIUS (DELTA_PRINTABLE_RADIUS - 10)
+  #define LEFT_PROBE_BED_POSITION -DELTA_PROBABLE_RADIUS
+  #define RIGHT_PROBE_BED_POSITION DELTA_PROBABLE_RADIUS
+  #define BACK_PROBE_BED_POSITION DELTA_PROBABLE_RADIUS
+  #define FRONT_PROBE_BED_POSITION -DELTA_PROBABLE_RADIUS   
+
+  // Non-linear bed leveling will be used.
+  // Compensate by interpolating between the nearest four Z probe values for each point.
+  // Useful for deltas where the print surface may appear like a bowl or dome shape.
+  // Works best with ACCURATE_BED_LEVELING_POINTS 5 or higher.
+  #define AUTO_BED_LEVELING_GRID_POINTS 9
+
+  // Offsets to the probe relative to the extruder tip (Hotend - Probe)
+  // X and Y offsets must be integers
+  #define X_PROBE_OFFSET_FROM_EXTRUDER 0     // -left  +right
+  #define Y_PROBE_OFFSET_FROM_EXTRUDER -10   // -front +behind
+  #define Z_PROBE_OFFSET_FROM_EXTRUDER -3.5  // -below (always!)
+
+  #define Z_RAISE_BEFORE_HOMING 4       // (in mm) Raise Z before homing (G28) for Probe Clearance.
+                                        // Be sure you have this distance over your Z_MAX_POS in case
+
+  #define XY_TRAVEL_SPEED 4000         // X and Y axis travel speed between probes, in mm/min
+
+  #define Z_RAISE_BEFORE_PROBING 15   //How much the extruder will be raised before traveling to the first probing point.
+  #define Z_RAISE_BETWEEN_PROBINGS 5  //How much the extruder will be raised when traveling from between next probing points
+  #define Z_RAISE_AFTER_PROBING 50    //How much the extruder will be raised after the last probing point.
+  
+  // Allen key retractable z-probe as seen on many Kossel delta printers - http://reprap.org/wiki/Kossel#Automatic_bed_leveling_probe
+  // Deploys by touching z-axis belt. Retracts by pushing the probe down. Uses Z_MIN_PIN.
+  //#define Z_PROBE_ALLEN_KEY
+  #ifdef Z_PROBE_ALLEN_KEY
+    #define Z_PROBE_ALLEN_KEY_DEPLOY_X 30
+    #define Z_PROBE_ALLEN_KEY_DEPLOY_Y DELTA_PRINTABLE_RADIUS
+    #define Z_PROBE_ALLEN_KEY_DEPLOY_Z 100
+    
+    #define Z_PROBE_ALLEN_KEY_RETRACT_X     -64
+    #define Z_PROBE_ALLEN_KEY_RETRACT_Y     56
+    #define Z_PROBE_ALLEN_KEY_RETRACT_Z     23
+    #define Z_PROBE_ALLEN_KEY_RETRACT_DEPTH 20
+  #endif
+  
+  //If defined, the Probe servo will be turned on only during movement and then turned off to avoid jerk
+  //The value is the delay to turn the servo off after powered on - depends on the servo speed; 300ms is good value, but you can try lower it.
+  // You MUST HAVE the SERVO_ENDSTOPS defined to use here a value higher than zero otherwise your code will not compile.
+
+//  #define PROBE_SERVO_DEACTIVATION_DELAY 300
+
+
+//If you have enabled the Bed Auto Leveling and are using the same Z Probe for Z Homing,
+//it is highly recommended you let this Z_SAFE_HOMING enabled!!!
+
+  #define Z_SAFE_HOMING   // This feature is meant to avoid Z homing with probe outside the bed area.
+                          // When defined, it will:
+                          // - Allow Z homing only after X and Y homing AND stepper drivers still enabled
+                          // - If stepper drivers timeout, it will need X and Y homing again before Z homing
+                          // - Position the probe in a defined XY point before Z Homing when homing all axis (G28)
+                          // - Block Z homing only when the probe is outside bed area.
+
+  #ifdef Z_SAFE_HOMING
+
+    #define Z_SAFE_HOMING_X_POINT (X_MAX_LENGTH/2)    // X point for Z homing when homing all axis (G28)
+    #define Z_SAFE_HOMING_Y_POINT (Y_MAX_LENGTH/2)    // Y point for Z homing when homing all axis (G28)
+
+  #endif
 
+#endif // ENABLE_AUTO_BED_LEVELING
 
 
 

Marlin/example_configurations/delta/Configuration_adv.h

 //===========================================================================
 
 #if defined (ENABLE_AUTO_BED_LEVELING) && defined (DELTA)
-  #error "Bed Auto Leveling is still not compatible with Delta Kinematics."
+
+  #if not defined(AUTO_BED_LEVELING_GRID)
+    #error "Only Grid Bed Auto Leveling is supported on Deltas."
+  #endif
+  
+  #if defined(Z_PROBE_SLED)
+    #error "You cannot use Z_PROBE_SLED together with DELTA."
+  #endif
+
+  #if defined(Z_PROBE_REPEATABILITY_TEST)
+    #error "Z-probe repeatability test is not supported on Deltas yet."
+  #endif
+
 #endif  
 
+#if defined(Z_PROBE_ALLEN_KEY)
+  #if !defined(AUTO_BED_LEVELING_GRID) || !defined(DELTA)
+    #error "Invalid use of Z_PROBE_ALLEN_KEY."
+  #endif
+#endif
+
 #if EXTRUDERS > 1 && defined TEMP_SENSOR_1_AS_REDUNDANT
   #error "You cannot use TEMP_SENSOR_1_AS_REDUNDANT if EXTRUDERS > 1"
 #endif

Marlin/planner.cpp

   st_wake_up();
 }
 
-#ifdef ENABLE_AUTO_BED_LEVELING
+#if defined(ENABLE_AUTO_BED_LEVELING) && not defined(DELTA)
 vector_3 plan_get_position() {
 	vector_3 position = vector_3(st_get_position_mm(X_AXIS), st_get_position_mm(Y_AXIS), st_get_position_mm(Z_AXIS));
 

Marlin/planner.h

 #ifdef ENABLE_AUTO_BED_LEVELING
 void plan_buffer_line(float x, float y, float z, const float &e, float feed_rate, const uint8_t &extruder);
 
-// Get the position applying the bed level matrix if enabled
-vector_3 plan_get_position();
+  #ifndef DELTA
+  // Get the position applying the bed level matrix if enabled
+  vector_3 plan_get_position();
+  #endif
 #else
 void plan_buffer_line(const float &x, const float &y, const float &z, const float &e, float feed_rate, const uint8_t &extruder);
 #endif // ENABLE_AUTO_BED_LEVELING