Building_Image_Steps

To prepare Kernel snap :
$ sudo snapcraft --target-arch arm64 snap

To prepare Gadget Snap :
$ snapcraft

$ cat << EOF > dragon-model.json
{
 "type": "model",
 "authority-id": "<auth-id>",
 "brand-id": "<auth-id>",
 "series": "16",
 "model": "dragonboard",
 "architecture": "arm64",
 "gadget": "dragonboard",
 "kernel": "ubuntu-snapdragon-kernel_4.4.0_arm64.snap",
 "timestamp": "$(date -Iseconds --utc)"
}
EOF

$ cat dragon-model.json | snap sign -k sh &> dragonboard.model


$ sudo /snap/bin/ubuntu-image -c beta --extra-snaps dragonboard_16.04-0.18_arm64.snap --extra-snaps ubuntu-snapdragon-kernel_4.4.0_arm64.snap -o dragonboard.img dragonboard.model

$ sudo dd if=dragonboard.img of=/dev/sdb bs=32M
$ sudo sync