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/arm64/boot/dts/digi/ 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 8M Nano system-on-module

The ConnectCore 8M Nano is a system-on-module (SOM) solution that integrates:

  • NXP i.MX8M Nano system-on-chip featuring many interfaces such as UART, CAN, SPI, and I2C

  • LPDDR4 memory

  • eMMC memory

  • PMIC chip

  • Crypto-authentication chip

  • Optional Wi-Fi + Bluetooth chip

  • Micro Controller Assist (MCA) chip

The ConnectCore 8M Nano 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 8M Nano system-on-module is offered in different variants, multiple .dtsi files have been defined to describe the hardware inside:

File Description

ccimx8mn.dtsi

Common hardware for ConnectCore 8M Nano system-on-module (SOM) variants

ccimx8mn-wb.dtsi

ConnectCore 8M Nano system-on-module variant with Wi-Fi and Bluetooth

Depending on your ConnectCore 8M Nano variant, your final platform .dts file will need to include one of these files.

ConnectCore 8M Nano Development Kit

The ConnectCore 8M Nano Development Kit is a carrier board assembling the ConnectCore 8M Nano system-on-module. The carrier board assembles additional hardware like a video port, Ethernet PHY, audio chip, PCIe minicard, microSD card holder, user LEDs, and so on.

As a final platform, the carrier board has a .dts file that includes one of the ConnectCore 8M Nano system-on-module .dtsi files.

Final platform files

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

File Digi product smart part number Wi-Fi Bluetooth

ccimx8mn-dvk-wb.dts

CC-WMX8MN-KIT

✓

✓

Graphical representation

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

ConnectCore 8M Nano Development Kit 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.