I was able to build my own image based on GitHub - SolidRun/meta-solidrun-arm-imx8. With cubox-i device I was able to enter u-boot with any keypress during startup, but on cubox-m I am not able to do this.
I need to set up constant MAC address in u-boot. How to do this? Right now every restart generates random MAC address and new IP address from DHCP.