RTOS for NIOS2 on MAX10

Hello,

could you advice me the realtime operating system for NIOS2 on MAX10 fpga ?

The best variant should be free operating system, but with free RTOS i was not be succesfull. MicroC/OS2 or some small linux ? I would need communicate with SD card (FAT system) and with some ethernet chip.

Thank you for your advice or experiences.

Jan Naceradsky, Czech Republic