Tweak ABL logging, document probing

Marlin/src/feature/bedlevel/abl/abl.cpp

  * Extrapolate a single point from its neighbors
  */
 static void extrapolate_one_point(const uint8_t x, const uint8_t y, const int8_t xdir, const int8_t ydir) {
+  if (!isnan(z_values[x][y])) return;
   if (DEBUGGING(LEVELING)) {
     DEBUG_ECHOPGM("Extrapolate [");
     if (x < 10) DEBUG_CHAR(' ');
     DEBUG_CHAR(ydir ? (ydir > 0 ? '+' : '-') : ' ');
     DEBUG_ECHOLNPGM("]");
   }
-  if (!isnan(z_values[x][y])) {
-    if (DEBUGGING(LEVELING)) DEBUG_ECHOLNPGM(" (done)");
-    return;  // Don't overwrite good values.
-  }
 
   // Get X neighbors, Y neighbors, and XY neighbors
   const uint8_t x1 = x + xdir, y1 = y + ydir, x2 = x1 + xdir, y2 = y1 + ydir;

Marlin/src/gcode/bedlevel/abl/G29.cpp

   // Restore state after probing
   if (!faux) restore_feedrate_and_scaling();
 
-  if (DEBUGGING(LEVELING)) DEBUG_ECHOLNPGM("<<< G29");
-
-  if (planner.leveling_active)
-    sync_plan_position();
+  // Sync the planner from the current_position
+  if (planner.leveling_active) sync_plan_position();
 
   #if HAS_BED_PROBE && defined(Z_AFTER_PROBING)
     probe.move_z_after_probing();
 
   report_current_position();
 
+  if (DEBUGGING(LEVELING)) DEBUG_ECHOLNPGM("<<< G29");
+
   G29_RETURN(isnan(measured_z));
 }
 

Marlin/src/module/probe.cpp

   const char Probe::msg_wait_for_bed_heating[25] PROGMEM = "Wait for bed heating...\n";
 #endif
 
-bool Probe::move_to_z(const float z, const feedRate_t fr_mm_s) {
-  if (DEBUGGING(LEVELING)) DEBUG_POS(">>> Probe::move_to_z", current_position);
+/**
+ * @brief Move down until the probe triggers or the low limit is reached
+ *
+ * @details Used by run_z_probe to get each bed Z height measurement.
+ *          Sets current_position.z to the height where the probe triggered
+ *          (according to the Z stepper count). The float Z is propagated
+ *          back to the planner.position to preempt any rounding error.
+ *
+ * @return TRUE if the probe failed to trigger.
+ */
+bool Probe::probe_down_to_z(const float z, const feedRate_t fr_mm_s) {
+  if (DEBUGGING(LEVELING)) DEBUG_POS(">>> Probe::probe_down_to_z", current_position);
 
   #if HAS_HEATED_BED && ENABLED(WAIT_FOR_BED_HEATER)
     // Wait for bed to heat back up between probing points
   // Tell the planner where we actually are
   sync_plan_position();
 
-  if (DEBUGGING(LEVELING)) DEBUG_POS("<<< Probe::move_to_z", current_position);
+  if (DEBUGGING(LEVELING)) DEBUG_POS("<<< Probe::probe_down_to_z", current_position);
 
   return !probe_triggered;
 }
   #if TOTAL_PROBING == 2
 
     // Do a first probe at the fast speed
-    if (move_to_z(z_probe_low_point, MMM_TO_MMS(Z_PROBE_SPEED_FAST))) {
+    if (probe_down_to_z(z_probe_low_point, MMM_TO_MMS(Z_PROBE_SPEED_FAST))) {
       if (DEBUGGING(LEVELING)) {
         DEBUG_ECHOLNPGM("FAST Probe fail!");
         DEBUG_POS("<<< run_z_probe", current_position);
     const float z = Z_CLEARANCE_DEPLOY_PROBE + 5.0 + (offset.z < 0 ? -offset.z : 0);
     if (current_position.z > z) {
       // Probe down fast. If the probe never triggered, raise for probe clearance
-      if (!move_to_z(z, MMM_TO_MMS(Z_PROBE_SPEED_FAST)))
+      if (!probe_down_to_z(z, MMM_TO_MMS(Z_PROBE_SPEED_FAST)))
         do_blocking_move_to_z(current_position.z + Z_CLEARANCE_BETWEEN_PROBES, MMM_TO_MMS(Z_PROBE_SPEED_FAST));
     }
   #endif
   #endif
     {
       // Probe downward slowly to find the bed
-      if (move_to_z(z_probe_low_point, MMM_TO_MMS(Z_PROBE_SPEED_SLOW))) {
+      if (probe_down_to_z(z_probe_low_point, MMM_TO_MMS(Z_PROBE_SPEED_SLOW))) {
         if (DEBUGGING(LEVELING)) {
           DEBUG_ECHOLNPGM("SLOW Probe fail!");
           DEBUG_POS("<<< run_z_probe", current_position);

Marlin/src/module/probe.h

   #endif
 
 private:
-  static bool move_to_z(const float z, const feedRate_t fr_mm_s);
+  static bool probe_down_to_z(const float z, const feedRate_t fr_mm_s);
   static void do_z_raise(const float z_raise);
   static float run_z_probe();
 };