Trying to boot an Orange Pi Zero2

I have been trying to get FreeBSD onto an Orange Pi Zero 2.
I can't even get as far as a U-Boot banner.  Nothing comes
through the serial port.  A Linux image boots just fine
using the serial port.  Linux uses MBR instead of GPT and
has a different boot environment with a lot of scripts.

From reading old documentation at wiki.freebsd.org it
seems like I should

1. Get an image for a 64 bit ARM SBC and write it to a card.
I tried both

    https://download.freebsd.org/releases/arm64/aarch64/ISO-IMAGES/14.0/FreeBSD-14.0-RELEASE-arm64-aarch64-PINE64-LTS.img.xz
    https://download.freebsd.org/releases/arm64/aarch64/ISO-IMAGES/14.0/FreeBSD-14.0-RELEASE-arm64-aarch64-RPI.img.xz

2. Make a new u-boot slave port with

    MODEL=         orangepi-zero2
    BOARD_CONFIG=  orangepi_zero2_defconfig
    FAMILY=        allwinner64

3. Run the dd command from
https://wiki.freebsd.org/arm/Allwinner/booting to install
the u-boot image at offset 128k in the SD card.  I
verified that the alternative address 8k has a long run of
zero bytes.

4. Copy sun50i-h616-orangepi-zero2.dtb from the Linux image
that works to the dtb directories on the FreeBSD image FAT
and UFS partitions.

I power up the Orange Pi and nothing happens.  It's
failing to load u-boot or else u-boot can't find the
serial port.  The quality of kernel support for the
Allwinner H616 doesn't matter here.  I see no sign that
the boot process gets as far as the FreeBSD loader.


What went wrong?  (If you know what went wrong, consider
updating wiki.freebsd.org to save the next victim.)

Is debugging with JTAG an option on this board?


If anybody on this list edits the online documentation,
wiki or www, it would be nice to have a list of what ARM
SBCs "just work".  I remember one of the Raspberry Pis
worked for me a few years ago.  A slightly different
configuration wouldn't have worked.  You needed less than
3 GB RAM and a certain board revision and you had to get
lucky with the version of U-Boot that was on the
releng-built image.