I don't know about an RTEMS CSP implementation. But maybe I can answer the rest of the questions: The tricky part is most likely CAN. There are only very few CAN drivers in RTEMS at the moment. For all other parts that are usually offered by an operating system like Zephyr or FreeRTOS, there should be equivalents. RTEMS also implements quite a lot of the POSIX API so that you most likely can re-use big parts of the Linux port.