Merge branch 'Marlin_v1' of https://github.com/ErikZalm/Marlin into typofixes_upstream

Marlin/Marlin_main.cpp

 // G10 - retract filament according to settings of M207
 // G11 - retract recover filament according to settings of M208
 // G28 - Home all Axis
-// G29 - Detailed Z-Probe, probes the bed at 3 points.  You must de at the home position for this to work correctly.
+// G29 - Detailed Z-Probe, probes the bed at 3 or more points.  Will fail if you haven't homed yet.
 // G30 - Single Z Probe, probes bed at current XY location.
 // G90 - Use Absolute Coordinates
 // G91 - Use Relative Coordinates
 
 #else // NOT DELTA
 
-      home_all_axis = !((code_seen(axis_codes[0])) || (code_seen(axis_codes[1])) || (code_seen(axis_codes[2])));
+      home_all_axis = !((code_seen(axis_codes[X_AXIS])) || (code_seen(axis_codes[Y_AXIS])) || (code_seen(axis_codes[Z_AXIS])));
 
       #if Z_HOME_DIR > 0                      // If homing away from BED do Z first
       if((home_all_axis) || (code_seen(axis_codes[Z_AXIS]))) {
             #error "You must have a Z_MIN endstop in order to enable Auto Bed Leveling feature!!! Z_MIN_PIN must point to a valid hardware pin."
             #endif
 
+            // Prevent user from running a G29 without first homing in X and Y
+            if (! (axis_known_position[X_AXIS] && axis_known_position[Y_AXIS]) )
+            {
+                LCD_MESSAGEPGM(MSG_POSITION_UNKNOWN);
+                SERIAL_ECHO_START;
+                SERIAL_ECHOLNPGM(MSG_POSITION_UNKNOWN);
+                break; // abort G29, since we don't know where we are
+            }
+
             st_synchronize();
             // make sure the bed_level_rotation_matrix is identity or the planner will get it incorectly
             //vector_3 corrected_position = plan_get_position_mm();
       }
       else
       {
-        bool all_axis = !((code_seen(axis_codes[0])) || (code_seen(axis_codes[1])) || (code_seen(axis_codes[2]))|| (code_seen(axis_codes[3])));
+        bool all_axis = !((code_seen(axis_codes[X_AXIS])) || (code_seen(axis_codes[Y_AXIS])) || (code_seen(axis_codes[Z_AXIS]))|| (code_seen(axis_codes[E_AXIS])));
         if(all_axis)
         {
           st_synchronize();