Working with Device Tree (DOULOS)

Intro#

• Device tree: for non-discoverable hardware, included in BSP
• Source type
  • Old style: C code BSP, files compiled into the kernel
  • New style: device-tree BSP -> device tree blob (load by boot loader)

Compilation#

In-tree vs. out-of-tree

dtc command

• convert .dts to .dtb, and backwards

Device tree syntax#

• devicetree.org

• Nodes

• Properties

  • Values

• Root node = /

• Values format

  • int, string, list of string, phandle (reference to other node)

• Standard properties

  • compatible
  • model = "vendor,board"
  • status = "okay"
  • For root node, memory map address must be specified
    • #address-cells = <1>
      • define the address length
      • 1 = 32-bit, 2 = 64-bit
    • #size-cells = <1>
      • define the size length
      • 1 = 32-bit, 2 = 64-bit
    • reg = <${base},${size}
      • address map
  • Mapping between device and CPU

• Must have cpus and memory@0 as nodes as well

• Special node

  • chosen
  • aliases
    • Alias to a full path of a device

• Interrupts

  • interrupt-controller empty property

  • #interrupt-cells: # of intps

  • Devices connect to the interrupt controller

    • interrupt-parent
    • interrupts
    • interrupt-names (optional)

Parsing the device tree#

• device_driver defines compatible
• Unified device proerty interface

Device tree overlays#

Other description language#

• Kernel v5.0 support YAML as well