The book is subject to copyright.
You cannot use the book, or parts of the book into your own publications, without the permission of the author.
I have put in most of the code a copyright with my mail address. This does not mean anything. It is just to let you know I modified existing code. The code has been tampered with …
Jan Jansen najnesnaj@yahoo.com
All the software is subject to the Apache 2.0 license (same as the Zephyr RTOS) A permissive license whose main conditions require preservation of copyright and license notices. Contributors provide an express grant of patent rights. Licensed works, modifications, and larger works may be distributed under different terms and without source code.
You could use nRF Connect SDK (often referred as NCS),it is Nordic Semiconductor SDK based on zephyr. It has additional features that could be useful for pinetime, namely bluetooth modules and bluetooth services. Important to mention that even though, NCS forks zephyr it is kept close to it and it is regularly updated to latest zephyr (typically every 2-3 weeks).
NCS is using BSD-5-Clause-Nordic license (https://github.com/NordicPlayground/fw-nrfconnect-nrf/blob/master/LICENSE) which is why I did not use their samples.
(see also : bluetooth serial communication)