[tesseract]

It was based on FreeRTOS, but FreeRTOS at the time was extremely bare bones and only provided a preemptive scheduler, task management, and synchronization primitives. Everything else (memory management, I/O, ...) had to come either from whatever libc implementation was in use, or be built from scratch.

[markus_zhang]

Thanks, does that mean early FreeRTOS is a good beginner project for OS study?

[tesseract]

In my opinion it's not always the most readable codebase, due to some idiosyncratic style choices, but it definitely has the advantages of being small and focused.