NixOS modules that make building images for raspberry-pi products easier. Most of the work in this repository is based on work in nixos-hardware and nixpkgs. Additionally, be aware that I am no expert and this repo is the product of me fooling around with some pis.

This flake provides nixos modules that correspond to different raspberry-pi products. These modules can be included in nixos configurations and aim to deliver the following benefits:

1. Configure the kernel, device tree, and u-boot in a way that is compatible with the hardware.
2. Provide a nix interface to device tree configuration that will be familiar to those who have used raspberry-pi's config.txt based configuration.
3. Make it easy to build an image suitable for flashing to an sd-card, without a need to first go through an installation media.

The important modules are overlay/default.nix, rpi/default.nix, and rpi/device-tree.nix. The other modules for i2c, i2s, etc are mostly wrappers that set common device tree settings for you.

{
  description = "raspberry-pi-nix example";
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-21.11";
    raspberry-pi-nix = {
      url = "github:tstat/raspberry-pi-nix";
      inputs.nixpkgs.follows = "nixpkgs";
    };
  };

  outputs = { self, nixpkgs, raspberry-pi-nix }:
    let
      inherit (nixpkgs.lib) nixosSystem;
      basic-config = { pkgs, lib, ... }: {
        time.timeZone = "America/New_York";
        users.users.root.initialPassword = "root";
        networking = {
          hostName = "basic-example";
          useDHCP = false;
          interfaces = { wlan0.useDHCP = true; };
        };
        hardware.raspberry-pi = {
          i2c.enable = true;
          audio.enable = true;
          fkms-3d.enable = true;
          deviceTree = {
            dt-overlays = [{
              overlay = "imx477"; # add the overlay for the HQ camera
              args = [ ];
            }];
          };
        };
      };
    in {
      nixosConfigurations = {
        rpi-zero-2-w-example = nixosSystem {
          system = "aarch64-linux";
          modules = [ raspberry-pi-nix.rpi-zero-2-w basic-config ];
        };
        rpi-4b-example = nixosSystem {
          system = "aarch64-linux";
          modules = [ raspberry-pi-nix.rpi-4b basic-config ];
        };
      };
    };
}

An image suitable for flashing to an sd-card can be found at the attribute config.system.build.sdImage. For example, if you wanted to build an image for rpi-zero-2-w-example in the above configuration example you could run:

nix build '.#nixosConfigurations.rpi-zero-2-w-example.config.system.build.sdImage'

The sd-image built is partitioned in the same way as the aarch64 installation media from nixpkgs: There is a firmware partition that contains necessary firmware, u-boot, and config.txt. Then there is another partition that contains everything else. After the sd-image is built, nixos system updates will not change anything in the firmware partition ever again. New kernels and device tree configurations will remain on the nixos partition and be booted by u-boot in the firmware partition.

So, while you can control device tree params and overlays through your nixos system configuration, if you want to modify other config.txt variables this must be done manually by mounting the partition and modifying the config.txt file.