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NixOS on ARM/Raspberry Pi 4: Difference between revisions

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→Audio: Update instructions for enabling audio. The old ones were broken.
m add udev rule for non-root access through libgpiod
 
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     raspberrypi-eeprom
     raspberrypi-eeprom
   ];
   ];
   system.stateVersion = "23.11";
   system.stateVersion = "24.11";
}
}
</nowiki>}}
=== <code>config.txt</code> ===
{{warning|Since 24.11, the option <code>boot.loader.raspberrypi</code> which included <code>firmwareConfig</code> is removed from <code>nixpkgs</code>, therefore changes have to be written to <code>config.txt</code> directly<ref>https://github.com/NixOS/nixpkgs/pull/241534</ref>}}
To edit options only available through <code>config.txt</code>, as of May 12, 2025, you can only do so non-declaratively:
{{commands|<nowiki>
$ sudo mount /dev/disk/by-label/FIRMWARE /mnt
$ sudo vim /mnt/config.txt # <-- make changes here
</nowiki>}}
For example, [https://www.raspberrypi-spy.co.uk/2020/11/overclocking-the-raspberry-pi-400/ overclocking] the Raspberry Pi 400 can be done by adding the following:
{{file|config.txt|text|<nowiki>
arm_freq=2000
over_voltage=6
</nowiki>}}
</nowiki>}}


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   # Enable audio devices
   # Enable audio devices
   boot.kernelParams = [ "snd_bcm2835.enable_hdmi=1" "snd_bcm2835.enable_headphones=1" ];
   boot.kernelParams = [ "snd_bcm2835.enable_hdmi=1" "snd_bcm2835.enable_headphones=1" ];
  boot.loader.raspberryPi.firmwareConfig = ''
    dtparam=audio=on
  '';
}
}
</nowiki>}}
{{file|config.txt|txt|<nowiki>
dtparam=audio=on
</nowiki>}}
</nowiki>}}


If you're running headless, you can also disable HDMI audio and force use of the headphones jack by adding <code>hdmi_ignore_edid_audio=1</code> on a line below <code>dtparam=audio=on</code>.
If you're running headless, you can also disable HDMI audio and force use of the headphones jack by adding <code>hdmi_ignore_edid_audio=1</code> on a line below <code>dtparam=audio=on</code>.
=== Networking ===
Ethernet and wifi interfaces should work out of the box. In addition to normal network configuration, consider disabling wifi powersaving if you experience slowness or issues with the host becoming unreachable on the network shortly after boot. For NetworkManager, the following configuration is sufficient:
{{file|/etc/nixos/configuration.nix|nix|<nowiki>
{
  # Basic networking
  networking.networkmanager.enable = true;
  # Prevent host becoming unreachable on wifi after some time.
  networking.networkmanager.wifi.powersave = false;
}
</nowiki>}}


=== Using GPIO pins as non-root ===
=== Using GPIO pins as non-root ===
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The <code>extraRules</code> changes the owner of <code>gpiomem</code> and all other files needed for GPIO to work to <code>root:gpio</code> and changes the permissions to <code>0660</code>.
The <code>extraRules</code> changes the owner of <code>gpiomem</code> and all other files needed for GPIO to work to <code>root:gpio</code> and changes the permissions to <code>0660</code>.
Therefore, the root user and anyone in the gpio group can now access the GPIO pins.
Therefore, the root user and anyone in the gpio group can now access the GPIO pins.
Permissions on the <code>/dev/gpiochip*</code> devices are needed to support access through the newer '''GPIO character device''' interface (see [https://libgpiod.readthedocs.io/en/latest/ libgpiod]).


<syntaxHighlight lang="nix">
<syntaxHighlight lang="nix">
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     SUBSYSTEM=="gpio", KERNEL=="gpiochip*", ACTION=="add", RUN+="${pkgs.bash}/bin/bash -c 'chown root:gpio /sys/class/gpio/export /sys/class/gpio/unexport ; chmod 220 /sys/class/gpio/export /sys/class/gpio/unexport'"
     SUBSYSTEM=="gpio", KERNEL=="gpiochip*", ACTION=="add", RUN+="${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+="${pkgs.bash}/bin/bash -c 'chown root:gpio /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value ; chmod 660 /sys%p/active_low /sys%p/direction /sys%p/edge /sys%p/value'"
     SUBSYSTEM=="gpio", KERNEL=="gpio*", ACTION=="add",RUN+="${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'"
    SUBSYSTEM=="gpio", KERNEL=="gpiochip*", ACTION=="add", RUN+="${pkgs.bash}/bin/bash -c 'chown root:gpio /dev/gpiochip* && chmod 0660 /dev/gpiochip*'"
   '';
   '';


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</syntaxhighlight>
</syntaxhighlight>


The the <code>spi0-0cd.dtso</code> file can be downloaded [https://github.com/raspberrypi/firmware/blob/master/boot/overlays/spi0-0cs.dtbo here].
The the <code>spi0-0cs.dtso</code> file can be downloaded [https://github.com/raspberrypi/firmware/blob/master/boot/overlays/spi0-0cs.dtbo here].
You might have to change the <code>compatible</code> field to "raspberrypi" in the dtbo file.
You might have to change the <code>compatible</code> field to "raspberrypi" in the dtbo file.


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   };  
   };  
</nowiki>}}
</nowiki>}}
== Customizing & Generating SD image without installation step ==
There's a nix-community project to support fine-grained kernel & config.txt, and generate the image directly:
[https://github.com/nix-community/raspberry-pi-nix/ nix-community/raspberry-pi-nix]


== Notes about the boot process ==
== Notes about the boot process ==
Retrieved from "https://wiki.nixos.org/wiki/NixOS_on_ARM/Raspberry_Pi_4"