View source for NixOS on ARM/Raspberry Pi 3

{{ARM/breadcrumb}}
<div class="infobox">
{|class="table"
!colspan="2" class="title"|Raspberry Pi 3 Family
|-
|colspan="2"|[[File:raspberry_pi_3_glamour.jpg|frameless|256px|A Raspberry Pi 3 with enclosure.]]
|-
!Manufacturer
|Raspberry Pi Foundation
|-
!Architecture
|AArch64
|-
!Bootloader
|Custom or U-Boot
|-
!Boot order
|SD, USB*
|-
!Maintainer
|
|-
!colspan="2" class="title"|Raspberry Pi 3B
|-
!SoC
|BCM2837
|-
!colspan="2" class="title"|Raspberry Pi 3B+
|-
!SoC
|BCM2837B0
|}
</div>
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 default Linux kernel in use, is the mainline Linux kernel, and not the Raspberry Pi Foundation's fork. This could reduce compatibility with some add-on boards or third-party libraries<sup>[expanded explanation needed]</sup>.

The Raspberry Pi 3 Family is only supported as '''AArch64'''. Use as armv7 is community supported.

== Board-specific installation notes ==

First follow the [[NixOS_on_ARM#Installation|generic installation steps]] to get the installer image and install using the [[NixOS_on_ARM#NixOS_installation_.26_configuration|installation and configuration steps]].

=== Raspberry Pi 3B and 3B+ ===

Both the AArch64 and ARMv7 images boot out-of-the-box. Using the 64-bit AArch64 image is highly recommended, as the availability of binaries is much better and allows the use of the 64-bit instruction set.

For the UART console, edit <code>/extlinux/extlinux.conf</code> on the boot partition of the SD card to set <code>console=ttyS1,115200n8</code> in the kernel boot parameters, and use the following GPIO Pins with an USB-TTL connector: 
<syntaxhighlight>
GND         - 3rd in top row, black cable
GPIO 14 TXD - 4th in top row, white cable
GPIO 15 RXD - 5th in top row, green cable
</syntaxhighlight>
Use <code>nix-shell -p screen --run "screen /dev/ttyUSB0 115200"</code> (or <code>nix run nixpkgs#screen -- /dev/ttyUSB0 115200</code> if you're using nix flakes) to connect to the console. 
{{note|The mainline kernel (tested with nixos kernel 4.18.7) [https://github.com/raspberrypi/linux/wiki/Upstreaming#downstream-drivers does not include support for cpu frequency scaling] on the Raspberry Pi. To get higher clock speed, set [https://www.raspberrypi.org/documentation/configuration/config-txt/overclocking.md <code><nowiki>force_turbo=1</nowiki></code>] in <code>/boot/config.txt</code> }}

<syntaxhighlight lang=nix>
{
  hardware.enableRedistributableFirmware = true;
  networking.wireless.enable = true;
}
</syntaxhighlight>

== Tools ==

The raspberry tools are available in the <code>raspberrypi-tools</code> package and include commands like <code>vcgencmd</code> to measure temperature and CPU frequency.

== Audio ==

In addition to the usual config, you will need to enable audio support explicitly in the firmwareConfig.

{{file|/etc/nixos/configuration.nix|nix|<nowiki>
  sound.enable = true;
  hardware.pulseaudio.enable = true;

  boot.loader.raspberryPi.firmwareConfig = ''
    dtparam=audio=on
  '';
</nowiki>}}
== Serial console==

Your <code>configuration.nix</code> will need to add <code>console=ttyS1,115200n8</code> to the <code>boot.kernelParams</code> configuration to use the serial console.

{{file|/etc/nixos/configuration.nix|nix|<nowiki>
{ config, pkgs, lib, ... }:
{
  boot.kernelParams = [
    "console=ttyS1,115200n8"
  ];
}
</nowiki>}}

If the Raspberry Pi downstream kernel is used the serial interface is named <code>serial0</code> instead.

== Bluetooth ==

The bluetooth controller is by default connected to the UART device at <code>/dev/ttyAMA0</code> and needs to be enabled through <code>btattach</code>:

{{file|/etc/nixos/configuration.nix|nix|<nowiki>
{ pkgs, ... }:
{
  systemd.services.btattach = {
    before = [ "bluetooth.service" ];
    after = [ "dev-ttyAMA0.device" ];
    wantedBy = [ "multi-user.target" ];
    serviceConfig = {
      ExecStart = "${pkgs.bluez}/bin/btattach -B /dev/ttyAMA0 -P bcm -S 3000000";
    };
  };
}
</nowiki>}}
== Camera ==

For the camera to work, you will need to add the following code to your configuration.nix: 

{{file|/etc/nixos/configuration.nix|nix|<nowiki>
{ config, pkgs, lib, ... }:
{
  boot.loader.raspberryPi.enable = true;
  # Set the version depending on your raspberry pi. 
  boot.loader.raspberryPi.version = 3;
  # We need uboot
  boot.loader.raspberryPi.uboot.enable = true;
  # These two parameters are the important ones to get the
  # camera working. These will be appended to /boot/config.txt.
  boot.loader.raspberryPi.firmwareConfig = ''
    start_x=1
    gpu_mem=256
  '';
}
</nowiki>}}
{{note| A reboot is required to load the new firmware configuration.}}

To make the camera available as v4l device under <code>/dev/video0</code> the <code>bcm2835-v4l2</code> kernel module need to be loaded. This can be done by adding the following code to your configuration.nix: 

{{file|/etc/nixos/configuration.nix|nix|<nowiki>
{ config, pkgs, lib, ... }:
{
  boot.kernelModules = [ "bcm2835-v4l2" ];
}
</nowiki>}}
== Notes about the boot process ==

It takes approximately 1 minute to boot a Pi 3B.

USB keyboards and HDMI displays should work, though some issues have been reported (see Troubleshooting below).

Using the 3.3v serial port via the pin headers (exact location depends on hardware version) will get u-boot output and, when configured, a Linux kernel console.

== Troubleshooting ==

=== Power issues ===

Especially with the power-hungry Raspberry Pi 3, it is important to have a [https://www.raspberrypi.org/documentation/hardware/raspberrypi/power/README.md sufficient enough power supply] or ''weirdness'' may happen. Weirdness may include:

* Lightning bolt on HDMI output "breaking" the display.
* Screen switching back to u-boot text
** Fixable temporarily when power is sufficient by switching VT (alt+F2 / alt+F1)
* Random hangs

This problem is a hard problem. It is caused by the Raspberry Pi warning about power issues, but the current drivers (as of 
Linux 4.14) have a hard time dealing with it properly. If the power supply is rated properly AND the cable is not incurring too much power losses, it may be required to disable the lightning bolt indicator so the display driver isn't messed up.<ref>https://logs.nix.samueldr.com/nixos/2017-12-20#1513784657-1513784714;</ref> The lightning bolt indicator can be disabled by adding the line <code>avoid_warnings=1</code> in config.txt<ref>https://www.raspberrypi.org/documentation/configuration/config-txt/README.md</ref>

{{note|A ''properly rated'' USB power supply, AND a good cable are necessary. The cable has to be short enough to not incur power losses through the length. Do note that thin and cheap cables usually have thinner copper wires, which in turn accentuates power losses.}}

===WiFi / WLAN===
For a possible solution to 802.11 wireless connectivity issues, see: https://github.com/NixOS/nixpkgs/issues/82462#issuecomment-604634627

===HDMI===

HDMI issues have been observed on the 18.09 AArch64 image. The display would hang on "Starting Kernel...", then act as if the HDMI cable was unplugged. Re-plugging the HDMI cable after boot fixed the issue, as did a different monitor and HDMI cable.

==== Early boot messages ====

To show boot messages from initrd with the mainline kernel, add this to <code>configuration.nix</code>.

<syntaxhighlight lang=nix>
{
  boot.initrd.kernelModules = [ "vc4" "bcm2835_dma" "i2c_bcm2835" ];
}
</syntaxhighlight>

=== Raspberry Pi 3B+ HDMI output issues ===

As of 2019/08/19, the u-boot build and kernel build can disagree about the name of the dtb file for the Raspberry Pi 3B+. This happens because the upstream filename has changed, and the built u-boot has hardcoded expectations for the filename to load.

For now, do not use <tt>linuxPackages_latest</tt>, use the default <tt>linuxPackages</tt> which is the latest LTS, 4.19, which is known to be compatible.

See {{issue|66960}}.

=== HDMI output issue with kernel 5.4 (NixOS 20.03 or NixOS unstable) ===

(Unverified for 5.5 or 5.6)

Some users have reported that the 5.4 kernel "hung at Starting kernel..." {{issue|82455}}. In all cases where it was possible to investigate, it was found that the device did boot, but that the HDMI out didn't function as expected.

It looks like it may be a setup-dependent issue, as a 20.03 image with 5.4 was verified as working.

If your setup is having the issue, first report on {{issue|82455}} with the Raspberry Pi model (important to note whether it is a plus or non-plus) and the kind of display used with the HDMI out, including whether it is using adapters or not.

Then, you can work around the issue by configuring your system to use the 4.19 kernel (previous LTS) using one of the following tricks.

# Use the serial console to configure the system, and <code>nixos-rebuild boot</code> it.
# Use a 19.09 image, specify the kernel in its configuration and upgrade to 20.03
# Boot the image, poweroff blindly using a keyboard, edit on another computer <code>/home/nixos/.ssh/authorized_keys</code> from the SD to add your key file, chmod as 600, unmount, boot the Raspberry Pi and find it on your network by some means.

<syntaxHighlight>
{
  boot.kernelPackages = pkgs.linuxPackages_4_19;
}
</syntaxHighlight>

===Additional Troubleshooting===

Additional troubleshooting information may be found [https://elinux.org/R-Pi_Troubleshooting at elinux.org].

<hr />