How to make a bootable armbian sd card for firefly rk3399?

[Somebody]

I  tried several times but failed.

[martinayotte]

You have to remember that all Rockchip SoC give priority boot order to eMMC against SDCard.

I don't own a Firefly, so I don't know if there switch or jumper or test points to disable eMMC to allow SDCard been booted.

Once you will be able to boot SDCard, installing Armbian on the eMMC will give you a interruptible U-Boot where you can hit <spacebar> to get promt and choose boot device using "setenv devnum <X>", either eMMC or SDCard, followed by "run mmc_boot".