Arduino software has historically always been licensed using the"GNU Lesser General Public License, version 2.1 or later" license formula (aka theLGPL-2.1-or-laterSPDX identifier).
This has always been the intent for the code in the ArduinoCore-API repository as well; however, there are several small issues that make this repository license not clearly defined:

there is no central LICENSE file;
some files in the repo do not have any license, even though they contain code taken from cores that were under theLGPL-2.1-or-later license;
CAN-related files have a subtly different license that did not include the "or later" clause;
files in thetest folder have copyright lines but no licensing information.

This PR addresses all these issues and converts all the repository to theLGPL-2.1-or-later license. Note that the authors of the code whose license has changed either are or were directly employed by Arduino, or had signed a CLA.

Note that some files have additional non-conflicting license terms; see each individual file for details.

pillo79 added5 commits

May 28, 2024 12:00

license: add missing license headers

a1f668d

Some of the files in the Arduino core were missing the license headers.They contain code which is either copied from previous Arduino cores(which were already LGPL-2.1-or-later), or has been submitted to thisrepository where most of the code is clearly LGPL-2.1-or-later.  In anycase, all the contributors have either been directly employed by Arduinoor have signed the CLA.Add the missing LGPL-2.1-or-later headers to the files.

license: update CAN files license to LGPL-2.1-or-later

a2735c0

The CAN files had a non-standard license which does not match the otherfiles in the repository. This commit updates the license header tomatch that of the other files.All of the contributors to these files have either been employed byArduino or have signed the CLA.

license: cosmetic updates

eeb0ce3

Minor updates to the license headers to make them more consistent amongthe repository.

license: add SPDX-License-Identifier to all files in test/

25be1ac

The files in the test/ folder had a copyright notice, but no licenseinformation. This commit adds the LGPL-2.1-or-later SPDX licenseidentifier to all these files.

license: add LICENSE file to the repository

3f3e8bd

All files in this repository are licensed under the GNU Lesser GeneralPublic License version 2.1. Make this obvious by including the LICENSEfile in the root of the repository.In addition to the above clause, some files may also be distributed underadditional license terms. See each individual file for details.