I think most knx projects that are on github or gitlab are GPL. I do not think the are much with BSD projects.
But http://www.knx.org has an overview of all certified drivers from different vendors. It may be possible to customize an existing driver from one of them.
https://www.knx.org/knx-en/for-manufacturers/members/
Weinzierl is one of the firms
https://weinzierl.de/index.php/en/all-knx/knx-stacks-en