Arduino Core for SAMD21 and SAMD51 CPU

This repository contains the source code and configuration files of the Arduino Core for Atmel's SAMD21 and SAMD51 processor (used on the Arduino/Genuino Zero, MKR1000 and MKRZero boards).

In particular, this adds support for the Seeed SAMD Boards such as the Seeeduino XIAO

Custom USB Serial Number Support

This fork adds the ability to set a custom USB serial number for SAMD devices instead of using the hardware-based serial number derived from the chip's unique ID.

Purpose

By default, SAMD microcontrollers use a serial number generated from hardware registers, which is unique for each chip but not customizable. This modification allows applications to:

• Set a user-defined USB serial number programmatically
• Maintain a consistent serial number across multiple devices for testing or deployment
• Identify devices by application-specific identifiers rather than hardware IDs

Usage

This fork supports both PlatformIO and Arduino IDE (tested on versions 2.3.6 and 2.3.7).

PlatformIO

To enable custom serial number support, define USB_CUSTOM_SERIAL in your build flags:

# In platformio.ini
build_flags = -DUSB_CUSTOM_SERIAL

Arduino IDE

To enable custom serial number support in Arduino IDE:

1. Install this board package

• Seeed ArduinoCore-samd needs to be added as well because of tools dependencies: openocd, CMSIS, CMSIS-Atmel, arduinoOTA: https://files.seeedstudio.com/arduino/package_seeeduino_boards_index.json
• Add this package: https://github.com/mszwaj/ArduinoCore-samd-custom-sn/releases/download/1.8.5-custom-sn.1-rc1/package_mszwaj_seeeduino_xiao_custom_sn.json
• Install "Seeed SAMD Boards" and "SAMD Boards (custom SN)"

2. Select your board: Tools → Board → SAMD Boards (custom SN) → Seeeduino XIAO (SN)
3. Enable custom serial: Tools → Custom Serial → Enabled

• this setting adds USB_CUSTOM_SERIAL build flag

When Custom Serial is set to Disabled, the device will use the default hardware-based serial number.

Set your custom serial number in code using:

char g_usbSerialNumber[33];

strcpy(g_usbSerialNumber, "MY-CUSTOM-SERIAL-001");
    
    // Your code...

Note: The custom serial number must be set before USB initialization. If g_usbSerialNumber is empty or USB_CUSTOM_SERIAL is not defined, the device will fall back to the hardware-based serial number.

Example

Example of usage with reading from flash before USB renumeration - keep it before setup():

class USBSerialInitializer {
public:
  USBSerialInitializer() {
    myFlashStorage.read(data);
    if (data.magicNumber == EEPROM_MAGIC_NUMBER) {
      strcpy(g_usbSerialNumber, data.sn);
    } else {
      uint32_t* uid = (uint32_t*)0x0080A00C;
      sprintf(g_usbSerialNumber, "%08lX%08lX%08lX%08lX", uid[0], uid[1], uid[2], uid[3]);
    }
  }
};

Implementation Details

• Custom serial numbers are limited to 32 characters (plus null terminator)
• The feature is opt-in via the USB_CUSTOM_SERIAL compile flag
• Without the flag, behavior is identical to the original Arduino Core
• Hardware serial number is used as fallback if custom serial is not set
• In Arduino IDE, the Tools → Custom Serial option (provided by boards.txt) automatically adds the USB_CUSTOM_SERIAL build flag when enabled

Bugs or Issues

If you find a bug you can submit an issue here on github:

https://github.com/Seeed-Studio/ArduinoCore-samd

or if it is an issue with the upstream:

https://github.com/arduino/ArduinoCore-samd/issues

Before posting a new issue, please check if the same problem has been already reported by someone else to avoid duplicates.

License and credits

This core has been developed by Arduino LLC in collaboration with Atmel.

  Copyright (c) 2015 Arduino LLC.  All right reserved.

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  See the GNU Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA