Small USB HID driver to activate Oculus Rift CV1 as extended display on Raspberry Pi 4

How to compile the driver

• Start RPi 4 and open a terminal
• Execute the following commands

sudo apt-get install libusb-1.0
git clone --recurse-submodules https://github.com/OhioIon/riftDriverPi
cd riftDriverPi
make

How to make Raspbian recognize the Oculus Rift CV1 as screen

Step 1 - Hardware connection

• Connect your normal screen to HDMI0
• Connect the Oculus Rift CV1 to HDMI1 and USB 3.0 port of the RPi 4

Step 2 - Rebuilding the kernel with increased framerate support

• The RPi kernel currently has a limitation of 85 Hz framerate for displays
• The Oculus Rift CV1 requires exactly 90 Hz framerate
• In order to get, patch and build the kernel execute the following commands in a terminal
• This follows the instructions of https://www.raspberrypi.org/documentation/linux/kernel/building.md

sudo apt install git bc bison flex libssl-dev make
cd ~
git clone --depth=1 https://github.com/raspberrypi/linux
cd linux

sed -i 's/if (drm_mode_vrefresh(mode) > 85)/if (drm_mode_vrefresh(mode) > 90)/g' drivers/gpu/drm/vc4/vc4_firmware_kms.c

KERNEL=kernel7l
make bcm2711_defconfig
make -j4 zImage modules dtbs
sudo make modules_install
sudo cp arch/arm/boot/dts/*.dtb /boot/
sudo cp arch/arm/boot/dts/overlays/*.dtb* /boot/overlays/
sudo cp arch/arm/boot/dts/overlays/README /boot/overlays/
sudo cp arch/arm/boot/zImage /boot/$KERNEL.img
sudo reboot

Step 3 - Configure screen resolution manually via RPi config.txt

• The Rift CV1 does not function like a normal screen
• It will only send hotplug over HDMI if it is enabled via a USB driver (which is too late for RPi)
• Also the EDID does not contain a standard timing information but only a single detailed timing descriptor
• In order to make it work, we need to explicitly apply the detailed timing spec in config.txt and force the hotplug
• The following lines need to be set in /boot/config.txt

hdmi_force_hotplug:1=1
hdmi_group:1=2
hdmi_mode:1=87
hdmi_timings:1=2160 1  8  32  40 1200 0  50 2 220 0 0 0 90 0 296750000 3

You can also use the config.txt provided as reference and copy it with:

sudo cp ~/riftDriverPi/config.txt /boot
sudo reboot

Now there is a second screen in the RPi 4 Screen Layout Editor (Preferences -> Screen Configuration) with resolution "FIXEDMODE".

Configure linux to use hidapi via libusb for Oculus Rift

• This will avoid having to run the application as root to access the USB device
• Execute the following commands in a terminal

echo 'SUBSYSTEM=="usb", ATTR{idVendor}=="2833", MODE="0666", GROUP="plugdev"' | sudo tee --append /etc/udev/rules.d/83-hmd.rules
sudo udevadm control --reload-rules
sudo reboot

Enable the Oculus Rift CV1 screen

• If the previous configuration steps have been completed, there is no need to repeat them
• In order to activate the Oculus Rift CV1 screen, just execute the riftDriverPi app
• The driver will enable the screen and send the keep-alive message cyclically

~/riftDriverPi/riftDriverPi

• You should see that the orange LED on the Rift turns white
• You should see the extended desktop through the Rift (but not nice since left and right eye see different parts)
• Test stereo view by watching a side-by-side video in full-screen on YouTube (https://www.youtube.com/results?search_query=3D+side+by+side)

Hint: Hitting return in the terminal will stop the application.