I got a pinetime development kit very early. I would like to thank the folks from https://www.pine64.org/ for the kit.
The Nordic nrf52832 is an Arm based, 32bit microcontroller with a lot of flash, RAM memory and(!) bluetooth! It is a good platform to explore the wonderful world of opensource RTOS’s. I choose the Zephyr platform, because it already contained the display driver, and the bluetooth functionality. Furthermore it can be updated wireless.
I started of with adapting simple samples, so they would run on the pinetime watch. Meanwhile I learned how to adapt the board definition file. Gradually this morphed into a pinetime-toolkit. A few experts contributed and improved this kit so it became usable.
I took a long break from this project, zephyr evolved and a project for creating an open source watch, the hypnos-firmware flourished.
The drivers for the heartrate sensor, touch panel that I adapted, became obsolete. The pinetime board definition file is now part of the zephyr RTOS distribution.
Recently I discovered that the standard focaltech touchscreen driver could be adapted easily so it would run on the pinetime and integrate nicely with the LVGL-gui. There were several OLED ssd1306 watches on my desk and I wondered if I could run Zephyr and LVGL (graphical stuff) on them as well. (yes, we can!) I played around with the “native_posix_64” board, which is a virtual board that allows you to run firmware on your computer instead of on the watch (no need for flashing).
This gave me the idea for an opensource-watch-framework. Start of with simple samples, and add some more functionality, until finally you end up with a smartwatch. The framework is build around three smartwatches, the pinetime, the ds_d6 and the posix_sdl. It should work on other platform as well, with minor modifications. I only recently got the idea for out-of-tree development. Just put all the modified drivers, board definitions and application in one place outside of the zephyr-tree.
A word of warning: this is work in progress.
You're likely to have a better skillset then me.
You are invited to add the missing pieces and to improve what's already there.