Add D100 Watchdog Test (#19697)

Marlin/src/gcode/gcode_d.cpp

@@ -25,8 +25,10 @@
 
   #include "gcode.h"
   #include "../module/settings.h"
+  #include "../module/temperature.h"
   #include "../libs/hex_print.h"
   #include "../HAL/shared/eeprom_if.h"
+  #include "../HAL/shared/Delay.h"
 
   /**
    * Dn: G-code for development and testing
@@ -84,6 +86,7 @@
         }
       } break;
 
+      #if ENABLED(EEPROM_SETTINGS)
         case 3: { // D3 Read / Write EEPROM
           uint8_t *pointer = parser.hex_adr_val('A');
           uint16_t len = parser.ushortval('C', 1);
@@ -128,6 +131,7 @@
             SERIAL_EOL();
           }
         } break;
+      #endif      
 
       case 4: { // D4 Read / Write PIN
         // const uint8_t pin = parser.byteval('P');
@@ -167,6 +171,20 @@
           SERIAL_EOL();
         }
       } break;
+
+      case 100: { // D100 Disable heaters and attempt a hard hang (Watchdog Test)
+        SERIAL_ECHOLN("Disabling heaters and attempting to trigger Watchdog");
+        SERIAL_ECHOLN("(USE_WATCHDOG " TERN(USE_WATCHDOG, "ENABLED", "DISABLED") ")");
+        thermalManager.disable_all_heaters();
+        delay(1000); // Allow time to print
+        DISABLE_ISRS();
+        // Use a low-level delay that does not rely on interrupts to function
+        // Do not spin forever, to avoid thermal risks if heaters are enabled and
+        // watchdog does not work.
+        DELAY_US(10000000);
+        ENABLE_ISRS();
+        SERIAL_ECHOLN("FAILURE: Watchdog did not trigger board reset.");
+      }
     }
   }