Nixos sd image and mainline uboot for Odroid N2

Suitable for a server. Make sure you have your UART.

Kernel patches sourced from the Armbian build.

Built regularily on the nix release-20.03 branch on arm64 hardware.

What's working

RTC
Boots from SD, USB, eMMC (tested)
ethaddr

What's not working

Resetting the network adapter (ip link set eth0 down/up) requires a reboot!
WOL
Linux desktop acceleration (needs panfrost drivers?) (won't fix)

Not tried

Audio

How to prepare a bootable drive.

Running nix-build links products under the ./result folder. You will need to build an image and uboot and write them to a drive to boot.

Build an image (on an aarch64 or x86_64 box)

nix-build release.nix -A sdImage

Then dd it to an sd card (or usb or eMMC)

DEV=/dev/mmcblkX
IMG=./result/???/sd-image-odroid-n2.img
dd if=$IMG of=$DEV conv=fsync bs=4M
sync

Build a u-boot (x86_64 box only :S)

Build the firmware package fip that packs u-boot ready for use.

nix-build release.nix -A fip

Then dd it to the sd card (or usb or eMMC)

DEV=/dev/mmcblkX
UBOOT=result/u-boot.bin
dd if=$UBOOT of=$DEV conv=fsync,notrunc bs=512 seek=1
sync

On your first boot

Upon first boot, you will need to setup a /etc/nixos/configuration.nix. Generate one using nixos-generate-config.

Afterwards, refer to the same profile.nix that the sd image was built from. This profile contains the board specific kernel package and configuration.

{ config, pkgs, lib, ... }:

{
  imports = [
    /etc/nixos/hardware-configuration.nix
    /etc/nixos/nix-odroid-n2/modules/profile.nix
  ];
}

Lessons learnt

When a cross-compiled image is used. NixOS will be rebuilt on the device natively when doing nixos-rebuild.
Cross-compiling is a means to get something going if you don't have any suitable arm64 hardware. Use arm64 hardware when you can.
When cross-compiling turn off everything you can till you get something that boots. For example, turn off sound, wifi or filesystem drivers.
You can build an image on arm64 hardware using nix on Armbian. Ensure you enable enough swap space ~15GB and have a 4GB model. This build will be much quicker because you can leverage the arm64 binary cache.
Cross-compiling is possible and has been done time to time. It bootstrapped this project. However it is not maintained as arm64 builds work better. YMMV.

References for guidance and patches

Armbian
LibreElec
Hardkernel forums

wav/nix-odroid-n2