Atomthreads RTOS supports the STM8 family of microcontrollers. It can be run on any STM8 hardware platform, including the low cost STM8S Discovery board, a very inexpensive platform for starting STM8 microcontroller development.

The STM8 port supports all of the three available STM8 compiler toolchains:

Atomthreads was the first free, open source RTOS available for the STM8, and is the only RTOS supporting the IAR compiler. The STM8 port supports all of the standard Atomthreads features found on the Features page. Released under the open and flexible BSD license, it is free for commercial or educational use without restriction.

The STM8 port comes with full instructions for running the sample applications and writing your own real time operating system applications for STM8. Separate instructions are provided for the Cosmic and IAR toolchains:

The STM8 CPU has a very limited number of CPU registers, leading the compiler vendors to augment the hardware registers with a number of virtual registers located in fast SRAM. These virtual registers are compiler-specific, hence the context switch scheme differs depending on the compiler used. Full details of the context switch schemes and registers can be found in the above documentation.