Installation from serial console
Maybe you built u-boot-rockchip.bin wrong, maybe try some image from
armbian or dietpi to see if your serial setup is correct
Uboot is not that important, all it has to do is get the kenel and dtb loaded in the right place
and set them going
So, for any working uboot, you can copy the 1st 16M and apply to any other SD card,
modify 1st sector/ mbr as needed (obviously for same SBC)
all uboot does is check and initialize mem, DASD and comms, then load OS
armbian or dietpi to see if your serial setup is correct
Uboot is not that important, all it has to do is get the kenel and dtb loaded in the right place
and set them going
So, for any working uboot, you can copy the 1st 16M and apply to any other SD card,
modify 1st sector/ mbr as needed (obviously for same SBC)
all uboot does is check and initialize mem, DASD and comms, then load OS