FreeRTOSがオープンソースと言えない理由 (2017-08-05)

FreeRTOSはいわゆるreal-time operating systemの実装の1つです。GPLv2に2つの例外条件を追加した"The FreeRTOS open source license"と呼ばれるライセンスの下で利用可能です。(同時に商用ライセンスも別途用意されています。)

しかしこのライセンスはOpen Source Initiative (OSI)に承認されておらず、厳密な意味でオープンソースとは言い難いものです。公式ページの説明では、クローズドソースの独立したモジュールをリンクすることを許す例外について強調されています:

Clause 1:

Linking FreeRTOS with other modules is making a combined work based on FreeRTOS.
Thus, the terms and conditions of the GNU General Public License V2 cover the
whole combination.

As a special exception, the copyright holders of FreeRTOS give you permission to
link FreeRTOS with independent modules to produce a statically linked
executable, regardless of the license terms of these independent modules, and to
copy and distribute the resulting executable under terms of your choice,
provided that you also meet, for each linked independent module, the terms and
conditions of the license of that module.  An independent module is a module
which is not derived from or based on FreeRTOS.


Clause 2:

FreeRTOS may not be used for any competitive or comparative purpose, including
the publication of any form of run time or compile time metric, without the
express permission of Real Time Engineers Ltd. (this is the norm within the
industry and is intended to ensure information accuracy).



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