Mainstream STM support has been upstreamed into the main tock kernel.
This repository contains ports of Tock for STM32 chips and Discovery/Nucleo boards. Learn more about Tock on the official website.
Follow the official getting started guide to setup your system to compile Tock and Tock applications.
Tock supports more than just STM32-based boards, take a look at the boards which are part of main repository too!