Hi,
I am just locked my self with new secure firmware :-( and when i try boot from sd card nothing happen immediatelly as i switch last jumper to boot from sd and power on both leds green and red are constantly on :-( I am thinking about using your method to downgrade  firmware to not secure one. You mentioned tftp server could you please give us more info how to replace kernel image in nand with tftp ? I think this will be very helpfull to community as bitmain is not playing fair ... May be easiest way will be just enable ssh throught serial console but i am not sure if this is possible. Many thanks for your help. MK