NVIDIA Jetson - Device Tree Overlay: Difference between revisions
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Revision as of 23:59, 16 February 2022
Introduction
This wiki is intended to be used as a reference If you want to create a Device Tree (DT) overlay for a custom hardware module. DT overlay is used to configure various hardware devices that may be attached to the system.
Nvidia Jetson kernels use a Device Tree (DT) to describe the hardware present in the Nvidia Jetson board. You can use Jetson‑IO to support a custom hardware module by creating a device tree overlay for the hardware module to allow optional external hardware to be described and configured.
Create a device tree overlay
Jetson‑IO
NVIDIA provides the Jetson Expansion Header Tool (also known as Jetson‑IO), a Python script that runs on a Jetson developer kit and lets you apply a DT overlay configuration through a graphic user interface. Jetson‑IO finds the overlay file and allows you to apply it.
Device tree overlay structure
A device tree overlay for a hardware module must define the property:
- fragment: A DT overlay comprises a number of fragments, each of which targets one node and its subnodes.
- overlay-name: which specifies a name for the hardware module.
- jetson-header-name: which specifies the expansion header with which the hardware module is associated; must specify one of the values described in the table jetson-header-name property values.
- compatible: which indicates which combination of Jetson module and carrier board the overlay supports; must specify one or more of the values described in the table compatible property values.
Creating a Simple Device Tree Overlay
To create a simple device tree overlay to add a new custom property for Jetson Xavier NX Developer Kit and attach it to the 40‑pin expansion header, create a file named my-overlay.dts on the target platform with the following contents:
/dts-v1/; /plugin/; / { overlay-name = "My Jetson Overlay Example"; jetson-header-name = "Jetson 40pin Header"; compatible = "nvidia,p3509-0000+p3668-0001"; fragment@0 { target-path = "/"; __overlay__ { my-custom-property = "This Is My Overlay"; }; }; };
Enter the following command to compile the DTS source file into an overlay file:
dtc -O dtb -o my-overlay.dtbo -@ my-overlay.dts
After you copy the new overlay file to the /boot directory, Jetson‑IO finds the overlay file and allows you to apply it, If you use an incorrect compatible value, the files is not listed
sudo cp my-overlay.dtbo /boot sudo /opt/nvidia/jetson-io/config-by-hardware.py -l
Configuration listed from Xavier NX
Configurations for the following hardware modules are available: 1. Adafruit SPH0645LM4H 2. FE-PI Audio V1 and Z V2 3. My Jetson Overlay example 4. ReSpeaker 4 Mic Array
Apply the device tree overlay created
sudo /opt/nvidia/jetson-io/config-by-hardware.py -n "My Jetson Overlay example"
To apply the changes is required to reboot the board. after reboot the board you can read the new property defined in the device tree using the DT overlay.
cat /proc/device-tree/my-custom-property
Output:
This Is My Overlay
Remove overlay changes applied
The changes of the DT overlay are applied in the DT original and are created a new device tree
/boot/kernel_tegra194-p3668-all-p3509-0000-my-jetson-overlay-example.dtb