Add A New Entry To The Yocto Device Tree For The Onwire Device

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Introduction

The Yocto Project is an open-source collaboration project that provides a flexible and customizable framework for building embedded Linux systems. One of the key components of the Yocto Project is the device tree, which is a data structure that describes the hardware components of a system. In this article, we will explore how to add a new entry to the Yocto device tree for an onwire device.

What is the Device Tree?

The device tree is a data structure that describes the hardware components of a system. It is a tree-like structure that contains information about the devices on the system, including their properties and relationships. The device tree is used by the Linux kernel to configure the system and provide information to device drivers.

Why Add a New Entry to the Device Tree?

There are several reasons why you might need to add a new entry to the device tree:

  • New Hardware: If you have new hardware that is not already supported by the device tree, you will need to add a new entry to describe it.
  • Customization: If you need to customize the behavior of a device or add new properties to it, you will need to add a new entry to the device tree.
  • Device Driver Development: If you are developing a new device driver, you will need to add a new entry to the device tree to describe the device and its properties.

Adding a Device Tree Overlay to the Yocto Build System

To add a new entry to the device tree, you will need to create a device tree overlay. A device tree overlay is a file that contains a modified version of the device tree that can be applied to the system.

Here are the steps to add a device tree overlay to the Yocto build system:

Step 1: Create a New Directory for the Overlay

Create a new directory in the meta layer of your Yocto build system. This directory will contain the device tree overlay.

mkdir -p meta/mycompany/recipes-devicetree/mydevice

Step 2: Create the Device Tree Overlay File

Create a new file in the mydevice directory. This file will contain the device tree overlay.

touch mydevice.dts

Step 3: Add the Device Tree Overlay to the device-tree.dtsi File

Add the device tree overlay to the device-tree.dtsi file. This file is located in the meta layer of the Yocto build system.

echo "/dts-v1/; /plugin/;/" >> device-tree.dtsi
echo "/ {"; >> device-tree.dtsi
echo "    compatible = \"mycompany,mydevice\";"; >> device-tree.dtsi
echo "    device_type = \"onwire\";"; >> device-tree.dtsi
echo "    reg = <0x10000000 0x10000000>;"; >> device-tree.dtsi
echo "};" >> device-tree.dtsi

Step 4: Add the Device Tree Overlay to the device-tree.dtb File

Add the device tree overlay to the device-tree.dtb file. This is located in the build directory of the Yocto build system.

echo "device-tree.dtsi" >> device-tree.dtb

Step 5: Update the device-tree.dtb File

Update the device-tree.dtb file to include the device tree overlay.

dtc -I dts -O dtb -o device-tree.dtb device-tree.dtsi

Step 6: Add the Device Tree Overlay to the device-tree.conf File

Add the device tree overlay to the device-tree.conf file. This file is located in the meta layer of the Yocto build system.

echo "device-tree-override = \"mydevice\"" >> device-tree.conf

Step 7: Rebuild the Yocto Image

Rebuild the Yocto image to include the device tree overlay.

bitbake -c buildall myimage

Example Use Case

Here is an example use case for adding a new entry to the device tree:

Suppose you have a new device that is an onwire device. You want to add a new entry to the device tree to describe this device.

Here is an example of how you might add a new entry to the device tree:

echo "/dts-v1/; /plugin/;/" >> device-tree.dtsi
echo "/ {"; >> device-tree.dtsi
echo "    compatible = \"mycompany,mydevice\";"; >> device-tree.dtsi
echo "    device_type = \"onwire\";"; >> device-tree.dtsi
echo "    reg = <0x10000000 0x10000000>;"; >> device-tree.dtsi
echo "};" >> device-tree.dtsi

This code adds a new entry to the device tree that describes the onwire device. The entry includes the compatible string, device type, and register information.

Conclusion

In this article, we explored how to add a new entry to the Yocto device tree for an onwire device. We discussed the importance of the device tree and how it is used by the Linux kernel to configure the system and provide information to device drivers. We also walked through the steps to add a device tree overlay to the Yocto build system and provided an example use case for adding a new entry to the device tree.

References

Q: What is the device tree and why is it important?

A: The device tree is a data structure that describes the hardware components of a system. It is a tree-like structure that contains information about the devices on the system, including their properties and relationships. The device tree is used by the Linux kernel to configure the system and provide information to device drivers.

Q: Why do I need to add a new entry to the device tree?

A: You may need to add a new entry to the device tree if you have new hardware that is not already supported by the device tree, if you need to customize the behavior of a device or add new properties to it, or if you are developing a new device driver.

Q: How do I add a new entry to the device tree?

A: To add a new entry to the device tree, you will need to create a device tree overlay. A device tree overlay is a file that contains a modified version of the device tree that can be applied to the system. You can create a device tree overlay by following the steps outlined in the previous article.

Q: What is a device tree overlay and how do I create one?

A: A device tree overlay is a file that contains a modified version of the device tree that can be applied to the system. You can create a device tree overlay by creating a new file in the meta layer of your Yocto build system and adding the necessary information to it.

Q: How do I add a new entry to the device tree overlay?

A: To add a new entry to the device tree overlay, you will need to add the necessary information to the file. This will typically include the compatible string, device type, and register information.

Q: What is the compatible string and why is it important?

A: The compatible string is a string that identifies the device and its properties. It is used by the Linux kernel to determine which device driver to use for the device.

Q: How do I determine the compatible string for my device?

A: You can determine the compatible string for your device by looking at the documentation for the device or by consulting with the manufacturer.

Q: What is the device type and why is it important?

A: The device type is a string that identifies the type of device. It is used by the Linux kernel to determine which device driver to use for the device.

Q: How do I determine the device type for my device?

A: You can determine the device type for your device by looking at the documentation for the device or by consulting with the manufacturer.

Q: What is the register information and why is it important?

A: The register information is a string that identifies the registers for the device. It is used by the Linux kernel to determine which device driver to use for the device.

Q: How do I determine the register information for my device?

A: You can determine the register information for your device by looking at the for the device or by consulting with the manufacturer.

Q: How do I apply the device tree overlay to the system?

A: You can apply the device tree overlay to the system by adding the necessary information to the device-tree.conf file and rebuilding the Yocto image.

Q: What are the benefits of adding a new entry to the device tree?

A: The benefits of adding a new entry to the device tree include:

  • Improved system configuration
  • Improved device driver functionality
  • Improved system performance

Q: What are the potential risks of adding a new entry to the device tree?

A: The potential risks of adding a new entry to the device tree include:

  • System instability
  • Device driver errors
  • System crashes

Q: How do I troubleshoot issues with the device tree?

A: You can troubleshoot issues with the device tree by:

  • Checking the device tree overlay for errors
  • Checking the device tree configuration for errors
  • Consulting with the manufacturer or documentation for the device

Conclusion

In this article, we have answered some of the most frequently asked questions about adding a new entry to the Yocto device tree. We have discussed the importance of the device tree, how to add a new entry to the device tree, and how to troubleshoot issues with the device tree. We hope that this article has been helpful in answering your questions and providing you with the information you need to add a new entry to the device tree.