The device tree is a data structure that describes the hardware components available on a system. The Linux kernel queries the device tree to know what drivers to load during boot.

Device tree file types

Device tree files are located at arch/arm/boot/dts/ and can have two extensions:

  • .dtsi files are device tree source include files. They describe hardware that is common to several platforms which include these files on their .dts files.

  • .dts files are device tree source files. They describe one specific platform.

ConnectCore 6UL system-on-module

The ConnectCore 6UL is a system-on-module (SOM) solution that integrates:

  • NXP i.MX6UL system-on-chip featuring many interfaces such as UART, CAN, SPI, and I2C

  • DDR3 memory

  • NAND memory

  • PMIC chip

  • Crypto-authentication chip

  • Optional Wi-Fi + Bluetooth chip

  • Micro Controller Assist (MCA) chip

The ConnectCore 6UL system-on-module needs to be soldered to a carrier board. For this reason, there is not a single .dts file for it. Instead, its hardware features are collected into .dtsi files that can be included by a final platform .dts. Since the ConnectCore 6UL system-on-module is offered in different variants, multiple .dtsi files have been defined to describe the hardware inside:

File Description

imx6ul-ccimx6ul.dtsi

Common hardware for ConnectCore 6UL system-on-module (SOM) variants

imx6ul-ccimx6ul-wb.dtsi

ConnectCore 6UL system-on-module variant with Wi-Fi and Bluetooth

Depending on your ConnectCore 6UL variant, your final platform .dts file will need to include one of these files.

ConnectCore 6UL SBC Express and ConnectCore 6UL SBC Pro

The ConnectCore 6UL SBC Express and ConnectCore 6UL SBC Pro are carrier boards assembling the ConnectCore 6UL system-on-module. Both boards assemble additional hardware such as Ethernet PHY, microSD card holder, user LEDs and so on.

As final platforms, both boards have .dts files that include one of the ConnectCore 6UL system-on-module .dtsi files.

Include files

Both the SBC Express and the SBC Pro boards can assemble different variants of the ConnectCore 6UL system-on-module, so the common hardware for the carrier boards is described in a board-specific .dtsi file:

File Description

imx6ul-ccimx6ulstarter.dtsi

Common hardware for ConnectCore 6UL SBC Express

imx6ul-ccimx6ulsbc.dtsi

Common hardware for ConnectCore 6UL SBC Pro

Final platform files

The final platforms are described in board-specific .dts files:

File Digi product smart part number Wi-Fi Bluetooth

imx6ul-ccimx6ulstarter-id129.dts

CC-WMX6UL-START

✓

✓

imx6ul-ccimx6ulsbc-id135.dts

CC-WMX6UL-KIT

✓

✓

imx6ul-ccimx6ulsbc-id136.dts

CC-SBP-WMX-JN7A

✓

✓

The device tree files without ID number are not linked to any Digi product. They correspond to:

Graphical representation

The following graphic illustrates the composition of a .dts file.

ConnectCore 6UL SBC Pro device tree files

Device tree selection during boot process

Digi Embedded Yocto builds the different device tree files (.dts) for different boards and SOM variants into binary device tree blobs (.dtb). The device tree blobs are placed inside the linux partition along with the kernel binary.

The bootloader uses the board_id variable to determine which device tree blob to use when booting the system. See Carrier board version and ID.

To learn how to create a device tree for your custom carrier board and using a custom board ID, see Add a new custom machine.