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| title: Raspberry Pi camera on NixOS | ||
| --- | ||
|
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||
| In this article, I describe how I configured my Raspberry Pi V1 camera module on | ||
| my Raspberry Pi 3 running NixOS. | ||
|
|
||
| The Raspberry Pi OS has [excellent support][RPi-Camera-Configuration] for many | ||
| camera modules. If you run the officially supported operating system, most | ||
| cameras work without any further configuration. | ||
|
|
||
| In my [Homelab][Homelab] I don't use the Raspberry Pi OS, but I run NixOS on all | ||
| my computers, including the Raspberry Pi. NixOS works well on the Pi, but the | ||
| camera module I own needs a special configuration. | ||
|
|
||
| # The "new" camera stack | ||
|
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||
| Four years ago, the Raspberry Pi team [released a new camera | ||
| stack][libcameraAnnouncement] that provides better access to the internals of | ||
| the camera system. Today, the old stack using Broadcom proprietary software is | ||
| unsupported and obsolete. Unfortunately, many online instructions and tutorials | ||
| [still refer to the Broadcom stack][CameraNotDetected] which renders them | ||
| irrelevant to the modern camera stack. | ||
|
|
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| The new camera stack comprises four layers: | ||
|
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| 1. Linux kernel with board-specific configuration | ||
| 1. Camera-specific drivers | ||
| 1. The libcamera library | ||
| 1. rpicam-apps camera utilities for taking photos and videos | ||
|
|
||
| The next sections describe how I configured these components on NixOS to use a | ||
| Raspberry Pi Version 1 camera module (Omnivision OV5647) with my Raspberry Pi | ||
| 3B. | ||
|
|
||
| ## Kernel | ||
|
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||
| The official NixOS installer works well on the Raspberry Pi. However, the camera | ||
| modules require some subsystems that are not enabled by default. | ||
|
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| Fortunately, it's easy to switch to a kernel tailored to the Raspberry Pi. For | ||
| my model 3B, I select the `linux_rp3` kernel package: | ||
|
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||
| ``` | ||
| { pkgs, ...}: | ||
| { | ||
| boot.kernelPackages = pkgs.linuxKernel.packages.linux_rpi3; | ||
| } | ||
| ``` | ||
|
|
||
| Actually, I don't adjust this parameter in [my configuration][HomelabHostRpi3], | ||
| but I import the `raspberry-pi-3` module from | ||
| [nixos-hardware][NixOSHardwareRPi3] which selects the correct kernel and tunes | ||
| a few other parameters too. | ||
|
|
||
| ## Camera driver (OV5647) | ||
|
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| The Raspberry Pi v1 camera module uses an Omnivision OV5647 image sensor. We | ||
| need to describe the OV5647 hardware to the kernel so that the sensor can be | ||
| controlled via the respective system calls. The data structure and language | ||
| for describing hardware is called the _device tree_. | ||
|
|
||
| The NixOS configuration block that enables the image sensor reads as follows: | ||
|
|
||
| ``` | ||
| { pkgs, ...}: | ||
| { | ||
| hardware.deviceTree.filter = "bcm2837-rpi-3*"; | ||
| hardware.deviceTree.overlays = [ | ||
| name = "ov5647-overlay"; | ||
| dtsText = ''' | ||
| ...ELIDED... | ||
| '''; | ||
| ] | ||
| } | ||
| ``` | ||
|
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| For brevity, I omitted the value of the `dtsText`. In my Homelab repository you | ||
| can read the full [device tree overlay configuration][HomelabDeviceTreeOverlay]. | ||
|
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| The `dtsText` string is a copy of the file | ||
| [ov5467-overlay.dts][ov5467-overlay.dts] from the Linux kernel source with one | ||
| modification: I changed the `compatible` property from `bcm2835` to `bcm2837`. | ||
| It turns out the OV546 device tree overlay is compatible with both BCM | ||
| chipsets, but I don't understand why overlay's source doesn't reflect this. | ||
|
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||
| I learned about this technique in [a GitHub issue | ||
| comment](https://github.com/NixOS/nixpkgs/issues/125354). It works™, the kernel | ||
| recognizes the image sensor on the I2C bus: | ||
|
|
||
| ``` | ||
| $ cat /sys/bus/i2c/devices/10-0036/name | ||
| ov5647 | ||
| ``` | ||
|
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||
| It was hard to get the device tree overlay working, but I'm not entirely | ||
| satisfied: fiddling with the device tree source files doesn't | ||
| feel right. | ||
|
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| Fortunately, the hardware configuration is done. Next, the software stack. | ||
|
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||
| ## libcamera | ||
|
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||
| The libcamera library drives the Raspberry Pi's camera system directly from | ||
| the Linux kernel, with minimal proprietary running on the Broadcom GPU. | ||
|
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| libcamera is part of [nixpkgs][NixpkgsLibcamera], but it's built without | ||
| support for the Raspberry Pi. I developed a [Nix package | ||
| overlay][HomelabLibcamera], based on the [Raspberry Pi specific libcamera | ||
| instructions][BuildLibcamera], which the compiles libcamera with a few | ||
| additional flags: | ||
|
|
||
| ``` | ||
| mesonFlags = old.mesonFlags ++ [ | ||
| "-Dcam=disabled" | ||
| "-Dgstreamer=disabled" | ||
| "-Dipas=rpi/vc4,rpi/pisp" | ||
| "-Dpipelines=rpi/vc4,rpi/pisp" | ||
| ]; | ||
| ``` | ||
|
|
||
| The upstream libcamera package uses the Meson build system. In the previous | ||
| snippet, `old.mesonFlags` refers to the upstream package's build flags. The | ||
| overlay appends to the original flag list enabling the Raspberry Pi specific | ||
| Image Processing Algorithms (IPAs) and pipelines. | ||
|
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||
| This example shows off the strength of the Nix Packages overlay systems: the | ||
| overlay describes the differences from the upstream package's build | ||
| instructions, like a _patch_ representing the differences between two versions | ||
| of a text file. | ||
|
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| ## rpicam-apps | ||
|
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| rpicam-apps is a set of command line applications, built on top of libcamera, | ||
| to capture images and video from a Raspberry Pi camera. | ||
|
|
||
| Based on a [draft pull-request in nixpkgs][NixpkgsLibcameraPR], I wrote [a Nix | ||
| derivation][HomelabRpicamApps] which builds rpicam-apps using my own libcamera | ||
| build and enabling only a minimal set of features. For example, I deactivate | ||
| support for preview windows and advanced post-processing capabilities. | ||
|
|
||
| # Picture time | ||
|
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||
| I collected the configuration I described in the previous sections in a [NixOS | ||
| module][HomelabCameraModule] which is imported from my [Raspberry Pi 3 host | ||
| configuration][HomelabHostRpi3]. | ||
|
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||
| After the configuration is deployed on the device, I can list the available | ||
| cameras: | ||
|
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| ``` text | ||
| $ rpicam-still --list-cameras | ||
| Available cameras | ||
| ----------------- | ||
| 0 : ov5647 [2592x1944 10-bit GBRG] (/base/soc/i2c0mux/i2c@1/ov5647@36) | ||
| Modes: 'SGBRG10_CSI2P' : 640x480 [58.92 fps - (16, 0)/2560x1920 crop] | ||
| 1296x972 [43.25 fps - (0, 0)/2592x1944 crop] | ||
| 1920x1080 [30.62 fps - (348, 434)/1928x1080 crop] | ||
| 2592x1944 [15.63 fps - (0, 0)/2592x1944 crop] | ||
| ``` | ||
|
|
||
| And, of course, I can take pictures: | ||
|
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||
| ``` | ||
| rpicam-still --output test-image.jpg | ||
| ``` | ||
|
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||
| INSERT IMAGE HERE | ||
|
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||
| I'm trying to to impress you with the image quality. The v1 camera module was | ||
| [released in 2013][v1Release], the modules available today have much better | ||
| sensors and optics. | ||
|
|
||
| # Summary | ||
|
|
||
| I use NixOS because the operating system is described in a declarative | ||
| configuration. The camera specific modifications I described in this article | ||
| are in a [NixOS module][HomelabCameraModule] which is included in my Raspberry | ||
| Pi's [host configuration][HomelabHostRpi3]. | ||
|
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||
| By choosing NixOS over the official Raspberry Pi OS, I set myself up to an | ||
| arduous journey. But, I learned about details of the camera stack, and now I | ||
| appreciate more the integration work done by the Raspberry Pi Foundation. | ||
|
|
||
| [BuildLibcamera]: https://www.raspberrypi.com/documentation/computers/camera_software.html#build-libcamera-and-rpicam-apps | ||
| [CameraNotDetected]: https://forums.raspberrypi.com/viewtopic.php?t=362707 | ||
| [HomelabCameraModule]: https://github.com/wagdav/homelab/blob/master/modules/camera-rpi-v1/default.nix | ||
| [HomelabDeviceTreeOverlay]: https://github.com/wagdav/homelab/blob/master/modules/camera-rpi-v1/default.nix#L34 | ||
| [HomelabHostRpi3]: https://github.com/wagdav/homelab/blob/master/host-rp3.nix | ||
| [Homelab]: https://github.com/wagdav/homelab | ||
| [HomelabRpicamApps]: https://github.com/wagdav/homelab/blob/master/modules/camera-rpi-v1/rpicam-apps.nix | ||
| [HomelabLibcamera]: https://github.com/wagdav/homelab/blob/master/modules/camera-rpi-v1/overlays/libcamera.nix | ||
| [libcameraAnnouncement]: https://www.raspberrypi.com/news/an-open-source-camera-stack-for-raspberry-pi-using-libcamera/ | ||
| [NixOSHardwareRPi3]: https://github.com/NixOS/nixos-hardware/blob/a59f00f5ac65b19382617ba00f360f8bc07ed3ac/raspberry-pi/3/default.nix#L7 | ||
| [NixpkgsLibcamera]: https://github.com/NixOS/nixpkgs/blob/4b616a8ecce7aaceea5360f9724065c182dc016f/pkgs/by-name/li/libcamera/package.nix | ||
| [NixpkgsLibcameraPR]: https://github.com/NixOS/nixpkgs/pull/281803 | ||
| [NixWikiCamera]: https://wiki.nixos.org/wiki/NixOS_on_ARM/Raspberry_Pi#Camera | ||
| [RPi-Camera-Configuration]: https://www.raspberrypi.com/documentation/computers/camera_software.html#configuration | ||
| [ov5467-overlay.dts]: (https://github.com/raspberrypi/linux/blob/rpi-6.1.y/arch/arm/boot/dts/overlays/ov5647-overlay.dts) | ||
| [v1Release]: https://www.raspberrypi.com/news/camera-board-available-for-sale/ |