bootstrapping nanopi neo2

[bch <brad.harder%gmail.com@localhost>]

I've built an image (same method as (successfully) used for plain
"neo"), and retrieved u-boot from pkgsrc (for neo2), and written to sd
card. When I try to boot the device over uart, though, I *immediately*
get:

U-Boot SPL 2017.11 (Nov 27 2017 - 19:15:54)
DRAM: 512 MiB
Trying to boot from MMC1




I don't get a countdown to interrupt, or any other signs of life.
*Once* I was able to enter u-boot params (I powered device while
sending interrupt via tip(1), but getting the prompt might have been
coincidental, as I haven't been able to repeat.

Anybody recognize what's going on here? I've been fiddling w/ this for
some time now, discussing w/ others, but am not making progress.

Regards,

-bch