NixOS on ARM/Raspberry Pi 4

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Raspberry Pi 4 Family
Manufacturer	Raspberry Pi Foundation
Architecture	AArch64
Bootloader	Custom or U-Boot
Boot order	Configurable; SD, USB, Netboot
Maintainer
Raspberry Pi 4B
SoC	BCM2711

The Raspberry Pi family of devices is a series of single-board computers made by the Raspberry Pi Foundation. They are all based on Broadcom System-on-a-chip (SoCs).

Status

The Raspberry Pi 4 Family is only supported as AArch64. Use as armv7 is community supported.

Board-specific installation notes

First follow the generic installation steps to get the installer image and install using the installation and configuration steps.

The Raspberry Pi 4B works with the generic SD image.

Sample instructions for installing NixOS on a Raspberry Pi are available at nix.dev.

Warning: Note that the Raspberry Pi 4 has two HDMI outputs, and apparently sometimes the user prompt for the console/TTY is displayed on HDMI 1 while the boot process is displayed on HDMI 0 (this may even be the case with the official (non NixOs) non-graphical lite image). So if after the message "Welcome on NixOs" at the end of phase 2 your screen goes black/disconnects, try to use the other HDMI port. See the related bug here.

Configuration

Using nixos-generate-config will generate the required minimal configuration.

For better GPU Support and some deviceTree quirks add the nixos-hardware channel:

nix-channel --add https://github.com/NixOS/nixos-hardware/archive/master.tar.gz nixos-hardware

nix-channel --update

/etc/nixos/configuration.nix

{ config, pkgs, lib, ... }:
{
  imports =
    [
      <nixos-hardware/raspberry-pi/4>
      ./hardware-configuration.nix
    ];
  hardware = {
    raspberry-pi."4".apply-overlays-dtmerge.enable = true;
    deviceTree = {
      enable = true;
      filter = "*rpi-4-*.dtb";
    };
  };
  console.enable = false;
  environment.systemPackages = with pkgs; [
    libraspberrypi
    raspberrypi-eeprom
  ];
  system.stateVersion = "23.11";
}

USB boot

For USB booting to work properly, a firmware update might be needed:

 $ nix-shell -p raspberrypi-eeprom
 $ rpi-eeprom-update -d -a

Now reboot the device so it can update the firmware from boot partition.

GPU support

The following configuration samples are built on the assumption that they are added to an already working configuration. They are not complete configurations.

Without GPU

/etc/nixos/configuration.nix

{
  services.xserver = {
    enable = true;
    displayManager.lightdm.enable = true;
    desktopManager.gnome.enable = true;
    videoDrivers = [ "fbdev" ];
  };
}

With GPU

In nixos-hardware#261 a new option has been added to use the fkms-3d overlay. This will only work with the vendor kernel.

/etc/nixos/configuration.nix

{ pkgs, ... }:

{
  imports = [
    .../nixos-hardware/raspberry-pi/4
  ];

  hardware.raspberry-pi."4".fkms-3d.enable = true;

  services.xserver = {
    enable = true;
    displayManager.lightdm.enable = true;
    desktopManager.gnome.enable = true;
  };
}

Tools

The raspberry tools are available in the libraspberrypi package and include commands like vcgencmd to measure temperature and CPU frequency.

Audio

In addition to the usual config, you will need to enable hardware audio support:

/etc/nixos/configuration.nix

  sound.enable = true;
  hardware.pulseaudio.enable = true;
  hardware.raspberry-pi."4".audio.enable = true;

Using GPIO pins as non root

By default, the GPIO pins are enable, but can only be accessed by the root user. This can be address by adding a udev rule to your configuration that changes the owner ship of /dev/gpiomem and the other required devices.

The following code adds a group gpio and adds the user mygpiouser to that group. You probably want to put your own user name here.

The extraRules change the owner of gpiomem and all other files needed for GPIO to work to root:gpio and changes the permissions to 0660. Therefore, the root user and anyone in the gpio group can now access the GPIO pins.

  # Create gpio group
  users.groups.gpio = {};

  # Change permissions gpio devices
  services.udev.extraRules = ''
    SUBSYSTEM=="bcm2835-gpiomem", KERNEL=="gpiomem", GROUP="gpio",MODE="0660"
    SUBSYSTEM=="gpio", KERNEL=="gpiochip*", ACTION=="add", RUN+="${pkgs.bash}/bin/bash -c 'chown root:gpio  /sys/class/gpio/export /sys/class/gpio/unexport ; chmod 220 /sys/class/gpio/export /sys/class/gpio/unexport'"
    SUBSYSTEM=="gpio", KERNEL=="gpio*", ACTION=="add",RUN+="${pkgs.bash}/bin/bash -c 'chown root:gpio /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value ; chmod 660 /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value'"
  '';

  # Add user to group
  users = {
    users.mygpiouser = {
      extraGroups = [ "gpio" ... ];
      ....
    };
  };

Enabling the SPI

To enable the SPI, you would normally add dtparam=spi=on to /boot/config.txt. This is not possbible on NixOS, and instead you have to apply a device tree overlay. For this we use the hardware.deviceTree.overlays option. After applying the overlay, we add an spi group and change the owner of the spidev device to it, similarly to GPIO.

hardware.raspberry-pi."4".apply-overlays-dtmerge.enable = true;
hardware.deviceTree = {
  enable = true;
  filter = "*-rpi-*.dtb";
  overlays = [
    {
      name = "spi";
      dtsoFile = ./spi0-0cd.dtso;
    }
  ];
};

users.groups.spi = {};

services.udev.extraRules = ''
  SUBSYSTEM=="spidev", KERNEL=="spidev0.0", GROUP="spi", MODE="0660"
'';

The the spi0-0cd.dtso file can be downlaoded here. You might have to change the compatible field to "raspberrypi" in the dtbo file.

HDMI-CEC

A few bits and pieces for using HDMI-CEC on the Pi4:

/etc/nixos/configuration.nix

{ pkgs, ... }:

{
  # an overlay to enable raspberrypi support in libcec, and thus cec-client
  nixpkgs.overlays = [
    # nixos-22.05
    # (self: super: { libcec = super.libcec.override { inherit (self) libraspberrypi; }; })
    # nixos-22.11
    (self: super: { libcec = super.libcec.override { withLibraspberrypi = true; }; })
  ];

  # install libcec, which includes cec-client (requires root or "video" group, see udev rule below)
  # scan for devices: `echo 'scan' | cec-client -s -d 1`
  # set pi as active source: `echo 'as' | cec-client -s -d 1`
  environment.systemPackages = with pkgs; [
    libcec
  ];

  services.udev.extraRules = ''
    # allow access to raspi cec device for video group (and optionally register it as a systemd device, used below)
    SUBSYSTEM=="vchiq", GROUP="video", MODE="0660", TAG+="systemd", ENV{SYSTEMD_ALIAS}="/dev/vchiq"
  '';

  # optional: attach a persisted cec-client to `/run/cec.fifo`, to avoid the CEC ~1s startup delay per command
  # scan for devices: `echo 'scan' > /run/cec.fifo ; journalctl -u cec-client.service`
  # set pi as active source: `echo 'as' > /run/cec.fifo`
  systemd.sockets."cec-client" = {
    after = [ "dev-vchiq.device" ];
    bindsTo = [ "dev-vchiq.device" ];
    wantedBy = [ "sockets.target" ];
    socketConfig = {
      ListenFIFO = "/run/cec.fifo";
      SocketGroup = "video";
      SocketMode = "0660";
    };
  };
  systemd.services."cec-client" = {
    after = [ "dev-vchiq.device" ];
    bindsTo = [ "dev-vchiq.device" ];
    wantedBy = [ "multi-user.target" ];
    serviceConfig = {
      ExecStart = ''${pkgs.libcec}/bin/cec-client -d 1'';
      ExecStop = ''/bin/sh -c "echo q > /run/cec.fifo"'';
      StandardInput = "socket";
      StandardOutput = "journal";
      Restart="no";
  };
}

Notes about the boot process

Unless using an extremely early WIP image, the Raspberry Pi 4B boots using the U-Boot platform firmware.

Updating U-Boot/Firmware

 
$ nix-shell -p raspberrypi-eeprom
$ sudo mount /dev/disk/by-label/FIRMWARE /mnt
$ sudo BOOTFS=/mnt FIRMWARE_RELEASE_STATUS=stable rpi-eeprom-update -d -a

source

Troubleshooting

Audio not playing and Bluetooth: no controller available

On the Raspberry Pi kernel, the jack may never play audio, and no Bluetooth devices may ever be found. To get this to work, it is recommended to switch to the mainline kernel. See nixpkgs#123725 for more info.

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