Option to ignore SD at startup (#20099)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

Marlin/Configuration_adv.h

@@ -1172,6 +1172,7 @@
   // Enable this option and set to HIGH if your SD cards are incorrectly detected.
   //#define SD_DETECT_STATE HIGH
 
+  //#define SD_IGNORE_AT_STARTUP            // Don't mount the SD card when starting up
   //#define SDCARD_READONLY                 // Read-only SD card (to save over 2K of flash)
 
   #define SD_PROCEDURE_DEPTH 1              // Increase if you need more nested M32 calls

Marlin/src/inc/SanityCheck.h

@@ -582,6 +582,11 @@
 /**
  * Serial
  */
+#ifndef SERIAL_PORT
+  #error "SERIAL_PORT must be defined in Configuration.h"
+#elif defined(SERIAL_PORT_2) && SERIAL_PORT_2 == SERIAL_PORT
+  #error "SERIAL_PORT_2 cannot be the same as SERIAL_PORT. Please update your configuration."
+#endif
 #if !(defined(__AVR__) && defined(USBCON))
   #if ENABLED(SERIAL_XON_XOFF) && RX_BUFFER_SIZE < 1024
     #error "SERIAL_XON_XOFF requires RX_BUFFER_SIZE >= 1024 for reliable transfers without drops."
@@ -594,12 +599,6 @@
   #error "SERIAL_XON_XOFF and SERIAL_STATS_* features not supported on USB-native AVR devices."
 #endif
 
-#ifndef SERIAL_PORT
-  #error "SERIAL_PORT must be defined in Configuration.h"
-#elif defined(SERIAL_PORT_2) && SERIAL_PORT_2 == SERIAL_PORT
-  #error "SERIAL_PORT_2 cannot be the same as SERIAL_PORT. Please update your configuration."
-#endif
-
 /**
  * Multiple Stepper Drivers Per Axis
  */
@@ -2194,6 +2193,14 @@ static_assert(hbm[Z_AXIS] >= 0, "HOMING_BUMP_MM.Z must be greater than or equal
   #endif
 #endif
 
+#if ENABLED(SD_IGNORE_AT_STARTUP)
+  #if ENABLED(POWER_LOSS_RECOVERY)
+    #error "SD_IGNORE_AT_STARTUP is incompatible with POWER_LOSS_RECOVERY."
+  #elif ENABLED(SDCARD_EEPROM_EMULATION)
+    #error "SD_IGNORE_AT_STARTUP is incompatible with SDCARD_EEPROM_EMULATION."
+  #endif
+#endif
+
 /**
  * Make sure only one display is enabled
  */

Marlin/src/sd/cardreader.cpp

@@ -425,7 +425,8 @@ void CardReader::manage_media() {
 
     if (stat) {                       // Media Inserted
       safe_delay(500);                // Some boards need a delay to get settled
-      mount();                        // Try to mount the media
+      if (TERN1(SD_IGNORE_AT_STARTUP, old_stat != 2))
+        mount();                      // Try to mount the media
       #if MB(FYSETC_CHEETAH, FYSETC_CHEETAH_V12, FYSETC_AIO_II)
         reset_stepper_drivers();      // Workaround for Cheetah bug
       #endif