diff --git a/Marlin/src/HAL/SAMD51/HAL.cpp b/Marlin/src/HAL/SAMD51/HAL.cpp
index bd1c98bfa1d9..8c102b643da8 100644
--- a/Marlin/src/HAL/SAMD51/HAL.cpp
+++ b/Marlin/src/HAL/SAMD51/HAL.cpp
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -18,6 +19,10 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  *
  */
+
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
 #ifdef __SAMD51__
 
 #include "../../inc/MarlinConfig.h"
diff --git a/Marlin/src/HAL/SAMD51/HAL.h b/Marlin/src/HAL/SAMD51/HAL.h
index 79ba8021f4fd..fe29d6c7f42d 100644
--- a/Marlin/src/HAL/SAMD51/HAL.h
+++ b/Marlin/src/HAL/SAMD51/HAL.h
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,6 +21,10 @@
  */
 #pragma once
 
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
+
 #define CPU_32_BIT
 
 #include "../shared/Marduino.h"
diff --git a/Marlin/src/HAL/SAMD51/HAL_SPI.cpp b/Marlin/src/HAL/SAMD51/HAL_SPI.cpp
index 77f4d5ecd513..58fdfe9499a1 100644
--- a/Marlin/src/HAL/SAMD51/HAL_SPI.cpp
+++ b/Marlin/src/HAL/SAMD51/HAL_SPI.cpp
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -19,6 +20,10 @@
  *
  */
 
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
+
 /**
  * Hardware and software SPI implementations are included in this file.
  *
diff --git a/Marlin/src/HAL/SAMD51/MarlinSerial_AGCM4.cpp b/Marlin/src/HAL/SAMD51/MarlinSerial_AGCM4.cpp
index a16ea2f75821..baa7a38503de 100644
--- a/Marlin/src/HAL/SAMD51/MarlinSerial_AGCM4.cpp
+++ b/Marlin/src/HAL/SAMD51/MarlinSerial_AGCM4.cpp
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -18,6 +19,10 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  *
  */
+
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
 #ifdef ADAFRUIT_GRAND_CENTRAL_M4
 
 /**
diff --git a/Marlin/src/HAL/SAMD51/MarlinSerial_AGCM4.h b/Marlin/src/HAL/SAMD51/MarlinSerial_AGCM4.h
index ac5a3793983e..1044d9fcd0ef 100644
--- a/Marlin/src/HAL/SAMD51/MarlinSerial_AGCM4.h
+++ b/Marlin/src/HAL/SAMD51/MarlinSerial_AGCM4.h
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,6 +21,10 @@
  */
 #pragma once
 
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
+
 #include "../../core/serial_hook.h"
 
 typedef Serial1Class<Uart> UartT;
diff --git a/Marlin/src/HAL/SAMD51/SAMD51.h b/Marlin/src/HAL/SAMD51/SAMD51.h
index 783956140d58..8cc19d7155c6 100644
--- a/Marlin/src/HAL/SAMD51/SAMD51.h
+++ b/Marlin/src/HAL/SAMD51/SAMD51.h
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,6 +21,10 @@
  */
 #pragma once
 
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
+
 #define SYNC(sc)    while (sc) {  \
                       asm("");    \
                     }
diff --git a/Marlin/src/HAL/SAMD51/Servo.cpp b/Marlin/src/HAL/SAMD51/Servo.cpp
index 665322fe24bc..e533eee30155 100644
--- a/Marlin/src/HAL/SAMD51/Servo.cpp
+++ b/Marlin/src/HAL/SAMD51/Servo.cpp
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -19,6 +20,10 @@
  *
  */
 
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
+
 /**
  * This comes from Arduino library which at the moment is buggy and uncompilable
  */
diff --git a/Marlin/src/HAL/SAMD51/ServoTimers.h b/Marlin/src/HAL/SAMD51/ServoTimers.h
index 948d515356fb..47e0a190aac9 100644
--- a/Marlin/src/HAL/SAMD51/ServoTimers.h
+++ b/Marlin/src/HAL/SAMD51/ServoTimers.h
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,6 +21,10 @@
  */
 #pragma once
 
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
+
 #define _useTimer1
 #define _useTimer2
 
diff --git a/Marlin/src/HAL/SAMD51/eeprom_flash.cpp b/Marlin/src/HAL/SAMD51/eeprom_flash.cpp
index 871bf22b7fc4..7d5518956c7a 100644
--- a/Marlin/src/HAL/SAMD51/eeprom_flash.cpp
+++ b/Marlin/src/HAL/SAMD51/eeprom_flash.cpp
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -18,6 +19,10 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  *
  */
+
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
 #ifdef __SAMD51__
 
 #include "../../inc/MarlinConfig.h"
diff --git a/Marlin/src/HAL/SAMD51/eeprom_qspi.cpp b/Marlin/src/HAL/SAMD51/eeprom_qspi.cpp
index faa763719707..1c82ede04032 100644
--- a/Marlin/src/HAL/SAMD51/eeprom_qspi.cpp
+++ b/Marlin/src/HAL/SAMD51/eeprom_qspi.cpp
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -18,6 +19,10 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  *
  */
+
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
 #ifdef __SAMD51__
 
 #include "../../inc/MarlinConfig.h"
diff --git a/Marlin/src/HAL/SAMD51/eeprom_wired.cpp b/Marlin/src/HAL/SAMD51/eeprom_wired.cpp
index 3481fe539c3e..7a03d4eaa34c 100644
--- a/Marlin/src/HAL/SAMD51/eeprom_wired.cpp
+++ b/Marlin/src/HAL/SAMD51/eeprom_wired.cpp
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -18,6 +19,10 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  *
  */
+
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
 #ifdef __SAMD51__
 
 #include "../../inc/MarlinConfig.h"
diff --git a/Marlin/src/HAL/SAMD51/endstop_interrupts.h b/Marlin/src/HAL/SAMD51/endstop_interrupts.h
index 2f02f404f5f1..e0e811c3a018 100644
--- a/Marlin/src/HAL/SAMD51/endstop_interrupts.h
+++ b/Marlin/src/HAL/SAMD51/endstop_interrupts.h
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,6 +21,10 @@
  */
 #pragma once
 
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
+
 /**
  * Endstop interrupts for ATMEL SAMD51 based targets.
  *
diff --git a/Marlin/src/HAL/SAMD51/fastio.h b/Marlin/src/HAL/SAMD51/fastio.h
index 79aede579044..0acf48131796 100644
--- a/Marlin/src/HAL/SAMD51/fastio.h
+++ b/Marlin/src/HAL/SAMD51/fastio.h
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,6 +21,10 @@
  */
 #pragma once
 
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
+
 /**
  * Fast IO functions for SAMD51
  */
diff --git a/Marlin/src/HAL/SAMD51/inc/SanityCheck.h b/Marlin/src/HAL/SAMD51/inc/SanityCheck.h
index 1b876c947dc7..ae1bc2f3efd5 100644
--- a/Marlin/src/HAL/SAMD51/inc/SanityCheck.h
+++ b/Marlin/src/HAL/SAMD51/inc/SanityCheck.h
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -18,6 +19,11 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  *
  */
+#pragma once
+
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
 
 /**
  * Test SAMD51 specific configuration values for errors at compile-time.
diff --git a/Marlin/src/HAL/SAMD51/pinsDebug.h b/Marlin/src/HAL/SAMD51/pinsDebug.h
index 639c4cd66eb9..94f91c77bcce 100644
--- a/Marlin/src/HAL/SAMD51/pinsDebug.h
+++ b/Marlin/src/HAL/SAMD51/pinsDebug.h
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,6 +21,10 @@
  */
 #pragma once
 
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
+
 #define NUMBER_PINS_TOTAL PINS_COUNT
 
 #define digitalRead_mod(p) extDigitalRead(p)
diff --git a/Marlin/src/HAL/SAMD51/spi_pins.h b/Marlin/src/HAL/SAMD51/spi_pins.h
index 2a667bcaa1ce..f1e4fd430246 100644
--- a/Marlin/src/HAL/SAMD51/spi_pins.h
+++ b/Marlin/src/HAL/SAMD51/spi_pins.h
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,6 +21,10 @@
  */
 #pragma once
 
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
+
 #ifdef ADAFRUIT_GRAND_CENTRAL_M4
 
  /*
diff --git a/Marlin/src/HAL/SAMD51/timers.cpp b/Marlin/src/HAL/SAMD51/timers.cpp
index 1ad0e360736a..7a211eb36a69 100644
--- a/Marlin/src/HAL/SAMD51/timers.cpp
+++ b/Marlin/src/HAL/SAMD51/timers.cpp
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -18,6 +19,10 @@
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  *
  */
+
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
 #ifdef __SAMD51__
 
 // --------------------------------------------------------------------------
diff --git a/Marlin/src/HAL/SAMD51/timers.h b/Marlin/src/HAL/SAMD51/timers.h
index 86e980c56690..86c324189223 100644
--- a/Marlin/src/HAL/SAMD51/timers.h
+++ b/Marlin/src/HAL/SAMD51/timers.h
@@ -1,8 +1,9 @@
 /**
  * Marlin 3D Printer Firmware
- *
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
- * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (c) 2011 Camiel Gubbels / Erik van der Zalm
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,6 +21,10 @@
  */
 #pragma once
 
+/**
+ * SAMD51 HAL developed by Giuliano Zaro (AKA GMagician)
+ */
+
 #include <stdint.h>
 
 // --------------------------------------------------------------------------