Dcodes: add D20/D21/D22 to generate/read/clear dumps

Firmware/Dcodes.cpp

@@ -924,5 +924,45 @@ void dcode_9125()
 }
 #endif //PAT9125
 
-
 #endif //DEBUG_DCODES
+
+#ifdef XFLASH_DUMP
+#include "xflash_dump.h"
+
+void dcode_20()
+{
+    if(code_seen('E'))
+        xfdump_full_dump_and_reset();
+    else
+    {
+        unsigned long ts = millis();
+        xfdump_dump();
+        ts = millis() - ts;
+        DBG(_N("dump completed in %lums\n"), ts);
+    }
+}
+
+void dcode_21()
+{
+    if(!xfdump_check_state())
+        DBG(_N("no dump available\n"));
+    else
+    {
+        KEEPALIVE_STATE(NOT_BUSY);
+        DBG(_N("D21 - read crash dump\n"));
+        print_mem(DUMP_OFFSET  + offsetof(dump_t, data),
+                  DUMP_SIZE, dcode_mem_t::xflash);
+    }
+}
+
+void dcode_22()
+{
+    if(!xfdump_check_state())
+        DBG(_N("no dump available\n"));
+    else
+    {
+        xfdump_reset();
+        DBG(_N("dump cleared\n"));
+    }
+}
+#endif

Firmware/Dcodes.h

@@ -29,6 +29,12 @@ extern void dcode_9(); //D9 - Read/Write ADC (Write=enable simulated, Read=disab
 extern void dcode_10(); //D10 - XYZ calibration = OK
 extern void dcode_12(); //D12 - Log time. Writes the current time in the log file.
 
+#ifdef XFLASH_DUMP
+extern void dcode_20(); //D20 - Generate an offline crash dump
+extern void dcode_21(); //D21 - Print crash dump to serial
+extern void dcode_22(); //D22 - Clear crash dump state
+#endif
+
 #ifdef HEATBED_ANALYSIS
 extern void dcode_80(); //D80 - Bed check. This command will log data to SD card file "mesh.txt".
 extern void dcode_81(); //D81 - Bed analysis. This command will log data to SD card file "wldsd.txt".

Firmware/Marlin_main.cpp

@@ -9205,8 +9205,56 @@ Sigma_Exit:
     ### D12 - Time <a href="https://reprap.org/wiki/G-code#D12:_Time">D12: Time</a>
     Writes the current time in the log file.
     */
-
 #endif //DEBUG_DCODES
+
+#ifdef XFLASH_DUMP
+    /*!
+    ### D20 - Generate an offline crash dump
+    Generate a crash dump for later retrival.
+    #### Usage
+
+     D20 [E]
+
+    ### Parameters
+    - `E` - Perform an emergency crash dump (resets the printer).
+    ### Notes
+    - A crash dump can be later recovered with D21, or cleared with D22.
+    - An emergency crash dump includes register data, but will cause the printer to reset after the dump
+      is completed.
+    */
+    case 20: {
+        dcode_20();
+        break;
+    };
+
+    /*!
+    ### D21 - Print crash dump to serial
+    Output the complete crash dump (if present) to the serial.
+    #### Usage
+
+     D21
+
+    ### Notes
+    - The starting address can vary between builds, but it's always at the beginning of the data section.
+    */
+    case 21: {
+        dcode_21();
+        break;
+    };
+
+    /*!
+    ### D22 - Clear crash dump state
+    Clear an existing internal crash dump.
+    #### Usage
+
+     D22
+    */
+    case 22: {
+        dcode_22();
+        break;
+    };
+#endif
+
 #ifdef HEATBED_ANALYSIS
 
     /*!