# Laser NixOS
Nix expressions for building a NixOS image for the Raspberry Pi 3 controlling the laser cutter in CCCHH.

## TL;DR
```shell
export \
MACHINE=raspberry-pi-3 \
SD_CARD=/dev/sda \
NIXPKGS_REV=dba4149

nix-build -I nixpkgs="https://github.com/NixOS/nixpkgs/archive/${NIXPKGS_REV}.tar.gz" -I machine=machines/$MACHINE --out-link out-links/$MACHINE
```

## Building
The ISO must be built by emulation if you are not building on an aarch64 machine.
Build your host NixOS with the following in the configuration.
```nix
  boot.binfmt.emulatedSystems = [
    "aarch64-linux"
  ];
```

### Machines
Select one of the [machines](./machines/) and set the environment variable.
```shell
export MACHINE=raspberry-pi-3
```

### `nixpkgs` Versions
Select a [nixpkgs](https://github.com/NixOS/nixpkgs/) version and set the enviroment variable.
```shell
export NIXPKGS_REV=dba4149
```

It's recommended to set it to one of the revision hashes from the table below.
But you can also set it to a branch name like `nixos-24.05`.

| ref         | rev       | date       |
|-------------|-----------|------------|
| nixos-24.05 | `dba4149` | 2024-11-07 |

### Build
```shell
nix-build -I nixpkgs="https://github.com/NixOS/nixpkgs/archive/${NIXPKGS_REV}.tar.gz" -I machine=machines/$MACHINE --out-link out-links/$MACHINE
```

## Flashing
Select the correct block device and set the environment variable.
```shell
export SD_CARD=/dev/sda
sudo sh -c "zstd -dcf out-links/$MACHINE/sd-image/*.img.zst | dd status=progress bs=64k iflag=fullblock oflag=direct of=$SD_CARD && sync && eject $SD_CARD"
```

## Deployment
For deploying new images without reflashing, you can use [NixOps](https://github.com/NixOS/nixops).

```shell
nix-shell -p nixops_unstable_minimal
```
Since stable NixOps reuqires Python2, we use the unstable version.
```shell
[nix-shell:~]$ nixops --version
NixOps 1.7-unstable-2024-02-28-pre-08feccb
```

### Create
```shell
nixops create -I nixpkgs="https://github.com/NixOS/nixpkgs/archive/${NIXPKGS_REV}.tar.gz" -I machine=machines/$MACHINE
```

### Deploy
```shell
nixops deploy -I nixpkgs="https://github.com/NixOS/nixpkgs/archive/${NIXPKGS_REV}.tar.gz" -I machine=machines/$MACHINE
```