Implement a validation check for the BLTouch

Marlin/Configuration_adv.h

@@ -905,6 +905,11 @@
    * Settings for all BLTouch and clone probes:
    */
 
+  // Safety: Check that the probe deployment can be detected before homing.
+  //         Cross-checks the endstop state when deployed/stowed and throws
+  //         an error if they don't differ. Requires Z_SAFE_HOMING.
+  //#define BLTOUCH_VALIDATE_ON_HOMING
+
   // Safety: The probe needs time to recognize the command.
   //         Minimum command delay (ms). Enable and increase if needed.
   //#define BLTOUCH_DELAY 500

Marlin/src/feature/bltouch.cpp

@@ -193,4 +193,21 @@ void BLTouch::mode_conv_proc(const bool M5V) {
   od_5v_mode = M5V;
 }
 
+#if ENABLED(BLTOUCH_VALIDATE_ON_HOMING)
+  /**
+   * Validate that the BLTouch deploys/stows and reports its state correctly.
+   */
+  bool BLTouch::validate() {
+    bool start_status, deploy_status, stow_status;
+    _stow();
+    start_status = status();
+    _deploy();
+    deploy_status = status();
+    _stow();
+    stow_status = status();
+
+    return ((start_status == stow_status) && (deploy_status != stow_status));
+  }
+#endif
+
 #endif // BLTOUCH

Marlin/src/feature/bltouch.h

@@ -78,6 +78,10 @@ class BLTouch {
 
   static float z_extra_clearance() { return high_speed_mode ? 7 : 0; }
 
+  #if ENABLED(BLTOUCH_VALIDATE_ON_HOMING)
+    static bool validate();
+  #endif
+
   // DEPLOY and STOW are wrapped for error handling - these are used by homing and by probing
   static bool deploy()              { return deploy_proc(); }
   static bool stow()                { return stow_proc(); }

Marlin/src/gcode/calibrate/G28.cpp

@@ -144,8 +144,13 @@
 
       TERN_(SENSORLESS_HOMING, safe_delay(500)); // Short delay needed to settle
 
-      do_blocking_move_to_xy(destination);
-      homeaxis(Z_AXIS);
+      if(TERN1(BLTOUCH_VALIDATE_ON_HOMING, bltouch.validate())) {
+        do_blocking_move_to_xy(destination);
+        homeaxis(Z_AXIS);
+      } else {
+        LCD_MESSAGE(MSG_BLTOUCH_VALIDATE_FAILED);
+        SERIAL_ECHO_MSG(STR_ERR_PROBING_FAILED);
+      }
     }
     else {
       LCD_MESSAGE(MSG_ZPROBE_OUT);

Marlin/src/inc/SanityCheck.h

@@ -4282,6 +4282,10 @@ static_assert(_PLUS_TEST(4), "HOMING_FEEDRATE_MM_M values must be positive.");
   #endif
 #endif
 
+#if ENABLED(BLTOUCH_VALIDATE_ON_HOMING) && DISABLED(Z_SAFE_HOMING)
+  #error "BLTOUCH_VALIDATE_ON_HOMING requires Z_SAFE_HOMING."
+#endif
+
 // Misc. Cleanup
 #undef _TEST_PWM
 #undef _NUM_AXES_STR

Marlin/src/lcd/language/language_en.h

@@ -570,6 +570,7 @@ namespace Language_en {
   LSTR MSG_BLTOUCH_MODE_STORE_OD          = _UxGT("Set BLTouch to OD");
   LSTR MSG_BLTOUCH_MODE_ECHO              = _UxGT("Report Drain");
   LSTR MSG_BLTOUCH_MODE_CHANGE            = _UxGT("DANGER: Bad settings can cause damage! Proceed anyway?");
+  LSTR MSG_BLTOUCH_VALIDATE_FAILED        = _UxGT("BLTouch validation failed!");
   LSTR MSG_TOUCHMI_PROBE                  = _UxGT("TouchMI");
   LSTR MSG_TOUCHMI_INIT                   = _UxGT("Init TouchMI");
   LSTR MSG_TOUCHMI_ZTEST                  = _UxGT("Z Offset Test");