NanoPi R5S

[Fred]

Hi arm@

I'm trying to boot the OpenBSD installer on a NanoPi R5S LTS, I have done:
dd if=miniroot76.img of=/dev/rsd2c bs=1m

but when I do:

dd if=u-boot-rockchip.bin of=/dev/sd2c seek=64

the bin file overwrites the msdos partition and part of the OpenBSD 
partition as the u-boot-rockchip.bin file is 9.1 Mb in size and the 
default msdos partition created by the first dd is only 7.9 Mb.

Am I missing something obvious or do I need build a bigger msdos 
partition on the sd card?

Cheers

Fred