@winterschon yes I have the boot log from both succesful and failed images. After numerous trial and errors (manual hook, compiled u-boot for r2s plus via ports), I found that there is no trust.img from FreeBSD, that's why nanopi skipped the sdcard. I flashed armbian (working image) trust.img to the sd card and Nanopi showed loader error.maybe I need to recompile the u-boot with ATF load turned off?