The software is based on Zephyr RTOS. I have modified some parts so I can take advantage of the syscall functionality and really make apps independent from the kernel. The apps are built independently as position independent codes which can be transferred over BLE. The apps are in the TINF format I created a while ago. ELF is just too large for microcontrollers.

The watch OS (Ratch OS) currently is the zephyr RTOS and a time API which an app can subscribe to. The app basically registers a callback with this API and the kernel periodically executes the call. I tackled this first so I can start building watch faces.

The UI is pretty simple, watchface -> menu -> app launch or submenu. There are 2 watchfaces and a sample app currently. Other menu items are just placeholders.