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
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:
Common hardware for ConnectCore 8M Nano system-on-module (SOM) variants
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:
|Digi product smart part number
The following graphic illustrates the composition of a .dts file.
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.