https://jaycarlson.net/embedded-linux/#am335x

When your microcontroller project outgrows its super loop and the random ISRs you’ve sprinkled throughout your code with care, there are many bare-metal tasking kernels to turn to —?FreeRTOS, ThreadX (now?Azure RTOS),?RT-Thread,?μC/OS, etc. By an academic definition, these are operating systems. However, compared to Linux, it’s more useful to think of these as a framework you use to write your bare-metal application inside. They provide the core components of an operating system: threads (and obviously a scheduler), semaphores, message-passing, and events. Some of these also have networking, filesystems, and other libraries.

Comparing bare-metal RTOSs to Linux simply comes down to the fundamental difference?between?these and Linux: memory management and protection. This one technical difference makes Linux running on an application processor behave quite differently from your microcontroller running an RTOS.1