mkdir /mnt/memdisk
mkdir /mnt/uboot

truncate -s 1100M bbb.img 
sudo mdconfig -f bbb.img

gpart create -s mbr md0
gpart add -t fat32 -b 1M -s 50M md0 # should this be *fat* not fat32? below we use F16 for fat.
sudo newfs_msdos -F16 /dev/md0s1
gpart add -t freebsd md0
sudo newfs /dev/md0s2

#build stuff

sudo -E make TARGET_ARCH=armv6 DESTDIR=/mnt/memdisk installworld distribution
sudo -E make installkernel  TARGET_ARCH=armv6 KERNCONF=BEAGLEBONE-MMCCAM DESTDIR=/mnt/memdisk

#.../ = /usr/ports/sysutils/u-boot-your-variant
cp ~/FreeBSD/hummingboard/obj/arm.armv6/usr/home/russellh/FreeBSD/hummingboard/src/sys/boot/arm/uboot/ubldr /mnt/uboot
cp .../work/u-boot-ports-v2017.01.00.2/MLO /mnt/uboot
cp .../work/u-boot-ports-v2017.01.00.2/u-boot.img /mnt/uboot

sudo umount /dev/md0s1 
sudo umount /dev/md0s2
sudo mdconfig -du md0

sysctl kern.geom.debugflags=16 
dd if=bbb.img of=/dev/da5 bs=4096k