Kernel driver for AR0234

Raspberry Pi kernel driver for Onsemi AR0234, a 2.3 MP global shutter 1/2.6" CMOS sensor.

• 2-lane and 4-lane MIPI CSI-2 (up to 900 Mbps/lane)
• 8-bit and 10-bit RAW output
• 1920×1200 @ 120 fps (full resolution)
• 960×600 @ 237 fps (2×2 binning)
• External trigger modes (pulsed, automatic, sync-sink)
• Flash output with programmable lead/lag delay

Setup

Install required tools:

sudo apt install -y git
sudo apt install -y --no-install-recommends dkms

Clone this repository:

cd ~
git clone https://github.com/Kurokesu/ar0234-v4l2-driver.git
cd ar0234-v4l2-driver/

Run setup script:

sudo ./setup.sh

Edit boot configuration:

sudo nano /boot/firmware/config.txt

Make two changes:

1. Find camera_auto_detect near the top and set it to 0:

camera_auto_detect=0

2. Add dtoverlay=ar0234 under the [all] section at the bottom of the file:

[all]
dtoverlay=ar0234

Save and exit. Reboot for changes to take effect.

Important

Stock libcamera does not support AR0234. You must build a patched version for camera to function. See Build libcamera below.

dtoverlay options

ar0234 overlay supports comma-separated options to override defaults:

option	description	default
cam0	Use cam0 port instead of cam1	cam1
4lane	Use 4-lane MIPI CSI-2 (if wired)	2 lanes
link-frequency=<Hz>	Set MIPI CSI-2 link frequency (Hz)	450000000
external-trigger	Pulse/automatic trigger mode via TRIG pin	off
sync-sink	Multi-sensor sync mode (frame timing locked to TRIG pin)	off
always-on	Keep regulator powered (prevents runtime PM power-off)	off
flash	Enable FLASH output pin (HIGH during exposure)	off
flash-lead=<n>	Flash lead delay (~3.4 µs/unit 4-lane, ~6.8 µs/unit 2-lane)	0
flash-lag=<n>	Flash lag delay (~3.4 µs/unit 4-lane, ~6.8 µs/unit 2-lane)	0

cam0

If camera is connected to cam0 port, append ,cam0:

dtoverlay=ar0234,cam0

4lane

To enable 4-lane MIPI CSI-2, append ,4lane:

dtoverlay=ar0234,4lane

Warning

Before using 4lane, confirm your camera port actually supports 4-lane MIPI CSI. Not all Raspberry Pi models and carrier boards provide 4-lane MIPI CSI on both ports.

link-frequency

Supported link frequencies: 450 MHz (default, 10-bit only) and 360 MHz (8-bit only). Sensor PLL constraints tie bit depth to link frequency, switch to 360 MHz if you need 8-bit output.

To set link frequency to 360 MHz, append ,link-frequency=360000000:

dtoverlay=ar0234,link-frequency=360000000

Output formats

Link frequency	Data rate / lane	Lanes	Bit depth	Width	Height	Max FPS
960×600 (2×2 binned)
360 MHz	720 Mbps	2	8	960	600	119 fps
450 MHz	900 Mbps	2	10	960	600	119 fps
360 MHz	720 Mbps	4	8	960	600	237 fps
450 MHz	900 Mbps	4	10	960	600	237 fps
HD 720p (sensor crop)
360 MHz	720 Mbps	2	8	1280	720	100 fps
450 MHz	900 Mbps	2	10	1280	720	100 fps
360 MHz	720 Mbps	4	8	1280	720	200 fps
450 MHz	900 Mbps	4	10	1280	720	200 fps
Full HD 1080p (sensor crop)
360 MHz	720 Mbps	2	8	1920	1080	67 fps
450 MHz	900 Mbps	2	10	1920	1080	67 fps
360 MHz	720 Mbps	4	8	1920	1080	134 fps
450 MHz	900 Mbps	4	10	1920	1080	134 fps
1920×1200 (full resolution)
360 MHz	720 Mbps	2	8	1920	1200	60 fps
450 MHz	900 Mbps	2	10	1920	1200	60 fps
360 MHz	720 Mbps	4	8	1920	1200	120 fps
450 MHz	900 Mbps	4	10	1920	1200	120 fps

Note

These framerates do not apply to pulsed trigger mode. See external-trigger.

Tip

Options can be combined. Example (cam0, 4-lane, 360 MHz):

dtoverlay=ar0234,cam0,4lane,link-frequency=360000000

Trigger modes

AR0234 supports two external trigger modes. Both use TRIG pin on camera module as external signal input. TRIG is a 1.8V logic level input wired directly to sensor. Trigger pulse only initiates capture, exposure time remains controlled by sensor's integration time register.

external-trigger

Sensor stays in standby and waits for activity on TRIG pin. Exposure and readout happen sequentially: readout does not begin until exposure is complete. Two sub-modes are available:

• Pulsed: each high pulse on TRIG pin captures a single frame (minimum pulse width 125 ns, 3 EXTCLK cycles at 24 MHz). Framerate is determined by pulse frequency.
• Automatic: if TRIG signal stays high, sensor outputs frames continuously at configured framerate.

dtoverlay=ar0234,external-trigger

---

When using rpicam-apps in pulsed trigger mode, start with a fixed shutter duration and gain:

rpicam-hello -t 0 --qt-preview --shutter 10000 --gain 2.0

Important

Always specify a fixed shutter duration and gain, to ensure the AGC does not try to adjust them automatically. With external trigger the AGC tends to go unstable.

Shutter value directly controls sensor exposure time and must satisfy:

exposure_time < trigger_period - (1 / max_fps) - ~1.6 ms

Where max_fps is maximum framerate for your mode from output formats table, and ~1.6 ms accounts for MIPI wakeup and internal sensor overhead. For example, at full resolution 4-lane 10-bit (max 120 fps) triggered at 30 Hz: 1/30 - 1/120 - 1.6 ms ≈ 23.7 ms maximum exposure time.

Maximum trigger frequency for pulsed mode:

Resolution	Lanes	Max trigger frequency
1920×1200 (full resolution)	2	30 Hz
	4	60 Hz
960×600 (2×2 binned)	2	60 Hz
	4	120 Hz

sync-sink

Sensor streams continuously but locks frame timing to external TRIG signal. Unlike external-trigger, exposure and readout overlap (pipelined), so higher framerates are possible. Trigger period must not be shorter than configured frame length.

dtoverlay=ar0234,sync-sink

---

Trigger modes can also be set at runtime via the module parameter:

# 0=off, 1=external-trigger, 2=sync-sink
echo 1 | sudo tee /sys/module/ar0234/parameters/trigger_mode

Note

Module parameter is global: in a multi-camera setup it applies to all AR0234 sensors. To configure each sensor independently, use device tree overlay options instead. Device tree setting takes precedence over module parameter.

always-on

always-on keeps camera regulator permanently enabled, preventing kernel from powering off sensor during runtime PM suspend.

dtoverlay=ar0234,always-on

Flash output

AR0234 has a FLASH output pin (1.8V logic level) that goes HIGH during sensor exposure, useful for synchronizing external illumination such as strobes or LEDs.

To enable flash output:

dtoverlay=ar0234,flash

By default, flash pulse closely follows exposure period (longer by ~8 µs on 4-lane or ~16 µs on 2-lane due to sensor overhead). The flash signal start can be shifted relative to exposure using flash-lead or flash-lag:

• flash-lead: flash starts before exposure, extending total flash time
• flash-lag: flash starts after exposure begins, shortening total flash time

Both accept values in the range 0 to 127, where each unit is approximately 3.4 µs (4-lane) or 6.8 µs (2-lane).

# Flash starts ~34 µs before exposure (4-lane)
dtoverlay=ar0234,4lane,flash,flash-lead=10

# Flash starts ~34 µs after exposure begins (4-lane)
dtoverlay=ar0234,4lane,flash,flash-lag=10

For most use cases, small delay values (single digits) are sufficient. Large delay values combined with short exposure times are not recommended. For short exposures (below ~450 µs on 4-lane or ~900 µs on 2-lane), flash-lead should not be used.

Note

In trigger mode, flash output is suppressed when the trigger pulse is shorter than ~1.5 ms.

Build libcamera

Main libcamera repository does not support AR0234. A fork with necessary modifications is available.

On Raspberry Pi, libcamera and rpicam-apps must be rebuilt together. Detailed instructions are available here, but for convenience, here is a shorter version.

Remove pre-installed rpicam-apps:

sudo apt remove --purge rpicam-apps

libcamera

Install dependencies:

sudo apt install -y libboost-dev
sudo apt install -y libgnutls28-dev openssl libtiff5-dev pybind11-dev
sudo apt install -y qtbase5-dev libqt5core5a libqt5gui5 libqt5widgets5
sudo apt install -y meson cmake
sudo apt install -y python3-yaml python3-ply
sudo apt install -y libglib2.0-dev libgstreamer-plugins-base1.0-dev

Clone Kurokesu's libcamera fork with AR0234 support:

cd ~
git clone https://github.com/Kurokesu/libcamera.git --branch ar0234
cd libcamera/

Configure with meson:

meson setup build --buildtype=release -Dpipelines=rpi/vc4,rpi/pisp -Dipas=rpi/vc4,rpi/pisp -Dv4l2=enabled -Dgstreamer=enabled -Dtest=false -Dlc-compliance=disabled -Dcam=disabled -Dqcam=disabled -Ddocumentation=disabled -Dpycamera=enabled

Build:

ninja -C build

Install:

sudo ninja -C build install

Tip

On devices with 1 GB of memory or less, build may exceed available memory. Append -j 1 to limit to a single process.

Warning

libcamera does not yet have a stable binary interface. Always build rpicam-apps after building libcamera.

rpicam-apps

Install dependencies:

sudo apt install -y cmake libboost-program-options-dev libdrm-dev libexif-dev
sudo apt install -y libavcodec-dev libavdevice-dev libavformat-dev libswresample-dev
sudo apt install -y libepoxy-dev libpng-dev

Clone Raspberry Pi's rpicam-apps repository:

cd ~
git clone https://github.com/raspberrypi/rpicam-apps.git
cd rpicam-apps

Configure with meson (libav enabled by default):

meson setup build -Denable_libav=enabled -Denable_drm=enabled -Denable_egl=enabled -Denable_qt=enabled -Denable_opencv=disabled -Denable_tflite=disabled -Denable_hailo=disabled

Important

On Raspberry Pi OS Bookworm, packaged libav* is too old for rpicam-apps newer than v1.9.0.

Bookworm libav workaround

Bookworm ships libavcodec 59.x while newer rpicam-apps expects libavcodec >= 60, causing build errors like "libavcodec API version is too old" (see Raspberry Pi forum thread).

• Keep libav by checking out rpicam-apps v1.9.0 before running meson setup:

  git checkout v1.9.0

• Disable libav if building rpicam-apps > v1.9.0:

  meson setup build -Denable_libav=disabled -Denable_drm=enabled -Denable_egl=enabled -Denable_qt=enabled -Denable_opencv=disabled -Denable_tflite=disabled -Denable_hailo=disabled

Build:

meson compile -C build

Install:

sudo meson install -C build

Tip

This should automatically update ldconfig cache. If you have trouble accessing your new build, update manually:

sudo ldconfig

Verify rpicam-apps build

Verify rpicam-apps was rebuilt correctly:

rpicam-hello --version

Expected output (build date will differ):

rpicam-apps build: v1.11.1 8b7be4ebfe18 24-02-2026 (19:30:43)
rpicam-apps capabilites: egl:1 qt:1 drm:1 libav:1
libcamera build: v0.0.0+6157-91924454

Verify that ar0234 is detected

Do not forget to reboot!

sudo reboot

List available cameras:

rpicam-hello --list-cameras

Expected output (varies by link frequency and lane configuration):

Available cameras
-----------------
0 : ar0234 [1920x1200 10-bit GRBG] (/base/axi/pcie@1000120000/rp1/i2c@80000/ar0234@10)
    Modes: 'SGRBG10_CSI2P' : 960x600 [236.85 fps - (0, 0)/1920x1200 crop]
                             1280x720 [198.49 fps - (320, 240)/1280x720 crop]
                             1920x1080 [133.58 fps - (60, 0)/1920x1080 crop]
                             1920x1200 [120.45 fps - (0, 0)/1920x1200 crop]

Special thanks

• 6by9 for sharing modded ar0234 driver and libcamera code.
• Will Whang for imx585-v4l2-driver, used as basis for structuring this driver.