Difference between revisions of "Device tree"

Revision as of 19:20, 23 June 2022

2021-08-23 Monday Starting notes for Device Tree, an OS independent framework with its own governance and steering committee, community, web site and on-line documentation. First Device Tree documentation noted here is:

• https://github.com/devicetree-org/devicetree-specification/releases/tag/v0.3

Today Monday studying section 4.0, "Device Bindings" and binding guidelines. May have questions for Jared Wolff of CircuitDojo, relating to his Quality Wing Zephyr driver project and specifically the files in Jared's AQW project.

Latest Zephyr documentation as of 2021-08-23 is here:

• https://docs.zephyrproject.org/latest/guides/dts/bindings.html
• https://docs.zephyrproject.org/latest/guides/dts/intro.html
• https://docs.zephyrproject.org/latest/guides/dts/howtos.html#dt-howtos
• https://docs.zephyrproject.org/latest/guides/dts/intro.html#devicetree-in-out-files

Related to or came up in search result in regards to '_P_label' no such symbol defined errors, when board overlay file not specified or not found:

• https://docs.zephyrproject.org/apidoc/latest/group__devicetree-generic-id.html

^ Some Historical Context

Some device tree historical context given in this Power Point presentation by Thomas Petazzoni of Free Electrons:

• https://elinux.org/images/f/f9/Petazzoni-device-tree-dummies_0.pdf

• https://www.nxp.com/docs/en/application-note/AN5125.pdf

^ Device Tree bindings files are yml format files

Noting that in AQW bindings file for SHCT3 sensor there is an include line:

Code excerpt, full file from Jared Wolff AQW driver:

#
# Copyright (c) 2021 Circuit Dojo LLC
#

description: Sensirion SHTC3 Temp/Humidity Sensor

compatible: "sensirion,shtc3"

include: i2c-device.yaml

The file i2c-device.yaml is found locally in /usr/local/share/ncs/v1.6.1/zephyr/dts/bindings/i2c/i2c-device.yaml, and this file contains:

Code excerpt, full file from Zephyr project:

# Copyright (c) 2017, Linaro Limited
# SPDX-License-Identifier: Apache-2.0

# Common fields for I2C devices

include: [base.yaml, power.yaml]

on-bus: i2c

properties:
    reg:
      required: true
      description: device address on i2c bus
    label:
      required: true

QUESTION: how does a developer know to include i2c-device.yaml?

^ Zephyr Device Tree API - A System Of Macros

• https://docs.zephyrproject.org/2.6.0/reference/devicetree/api.html

== ^ 0408 - Undocumented Device Tree syntax and features . . . Early Google search result when seeking info on `/delete-property/` token in Device Tree Source file, observed specifically in Jared Wolff (Circuit Dojo) nfed release tag v1.7.1, active_sleep sample app board overlay file.

• https://elinux.org/Device_Tree_Source_Undocumented