Device Tree / basic build

On the BBB, there are three essential steps to create and run a Device Tree file:

1. Create a source file (dts).

2. Compile it and make a binary (dtb)—also known as blob—of the file.

3. Ensure that the kernel knows where to find the new blob.

Let's start with a simple recipe, one that turns off one of the onboard LEDs: specifically, USR0, which is the LED that blinks with the "heartbeat" pattern. There are simpler ways to do this, as we did the same thing with BoneScript in Chapter 3, Physical Computing Recipes Using JavaScript, the BoneScript Library, and Python. However, it remains a useful introductory recipe to understand Device Tree's interaction with the kernel.

Getting ready

For the next recipe, simply power up your board via the USB port. Internet connectivity is not required.

How to do it...

You need to perform the following steps:

1. Log in as root with this command:

   $ sudo -i
   #
   

2. Grab the file that we need for this recipe. Going forward in the book, we will more commonly have...