Boot from SATA drive

I downloaded the rasbian jessie image for a BPI-M! from 2016-07-12. I would like to use root from a disk attached to the SATA, as I did previously with bananian.

However, whatever I try I can not get it to boot from anything different than /dev/mmcblk0p2. I tried putting “root=/dev/sda1” in cmdline.txt, boot.cmd, config.txt and uEnv.txt. Yes, I created a new boot.scr.

Help? Updated few weeks ago. Not in 2016.