Mandate all probe cycles ignore feed overrides.

- For repeatability reasons, all G38.x probe cycles ignore feed rate
overrides and move at their programmed speed.

- The mandate can be removed with a new config.h option.

- Updated the documentation to reflect the change.

grbl/config.h

@@ -540,6 +540,13 @@
 // that any of these commands are used need continuous motions through them.
 #define FORCE_BUFFER_SYNC_DURING_WCO_CHANGE // Default enabled. Comment to disable.
 
+// By default, Grbl disables feed rate overrides for all G38.x probe cycle commands. Although this
+// may be different than some pro-class machine control, it's arguable that it should be this way. 
+// Most probe sensors produce different levels of error that is dependent on rate of speed. By 
+// keeping probing cycles to their programmed feed rates, the probe sensor should be a lot more
+// repeatable. If needed, you can disable this behavior by uncommenting the define below.
+// #define ALLOW_FEED_OVERRIDE_DURING_PROBE_CYCLES // Default disabled. Uncomment to enable.
+
 // Enables and configures parking motion methods upon a safety door state. Primarily for OEMs
 // that desire this feature for their integrated machines. At the moment, Grbl assumes that
 // the parking motion only involves one axis, although the parking implementation was written

grbl/gcode.c

@@ -1040,6 +1040,9 @@ uint8_t gc_execute_line(char *line)
       } else {
         // NOTE: gc_block.values.xyz is returned from mc_probe_cycle with the updated position value. So
         // upon a successful probing cycle, the machine position and the returned value should be the same.
+        #ifndef ALLOW_FEED_OVERRIDE_DURING_PROBE_CYCLES
+          pl_data->condition |= PL_COND_FLAG_NO_FEED_OVERRIDE;
+        #endif
         uint8_t is_probe_away = false;
         uint8_t is_no_error = false;
         if ((gc_state.modal.motion == MOTION_MODE_PROBE_AWAY) || (gc_state.modal.motion == MOTION_MODE_PROBE_AWAY_NO_ERROR)) { is_probe_away = true; }

grbl/report.c

@@ -569,6 +569,9 @@ void report_build_info(char *line)
     #ifdef LIMITS_TWO_SWITCHES_ON_AXES
       serial_write('L');
     #endif
+    #ifdef ALLOW_FEED_OVERRIDE_DURING_PROBE_CYCLES
+      serial_write('A');
+    #endif
     #ifdef USE_CLASSIC_GRBL_INTERFACE
       serial_write('R');
     #endif