ksachdeva Zephyr Kconfig Skill
Expert guidance on Zephyr's Kconfig system for build-time configuration, symbol definition, and dependency management.
Table of Contents
Core Concepts
Define vs. Configure (CRITICAL)
| Action | File | Syntax |
|---|---|---|
| Define symbol | Kconfig |
config MY_FEAT (NO prefix) |
| Configure value | prj.conf |
CONFIG_MY_FEAT=y (WITH prefix) |
Symbol Types
- bool:
yorn - int: Integer value
- hex: Hexadecimal value
- string: Quoted text
Key Files After Build
build/zephyr/.config— Final resolved configurationbuild/zephyr/kconfig/Kconfig.modules— Auto-generated module Kconfigs
Common Workflows
1. Defining Symbols in Kconfig
Create new configuration options for drivers, modules, or apps.
- Syntax (types, menus, choices, conditionals): See syntax.md
- Best practices (naming, placement, dependencies): See best_practices.md
Quick Example:
config MY_DRIVER_ENABLE
bool "Enable My Driver"
depends on I2C
help
Enable support for My Driver over I2C.
2. Configuring Applications
Set values in prj.conf or board-specific overlays.
| Type | Example |
|---|---|
| Boolean | CONFIG_LOG=y |
| Integer | CONFIG_MAIN_STACK_SIZE=2048 |
| String | CONFIG_BT_DEVICE_NAME="MyDevice" |
| Hex | CONFIG_FLASH_BASE_ADDRESS=0x08000000 |
3. Using Menuconfig
Interactive configuration exploration and modification.
- Launch and navigate menuconfig: See menuconfig.md
west build -t menuconfig
4. Writing Module Kconfig
Integrate external modules with Zephyr's build system.
- Module integration details: See best_practices.md
Configuration Files
Application Level
| File | Purpose |
|---|---|
prj.conf |
Main app configuration |
boards/<board>.conf |
Board-specific overrides |
app.overlay |
Devicetree + Kconfig overlay |
Module/Driver Level
| File | Purpose |
|---|---|
Kconfig |
Symbol definitions |
zephyr/module.yml |
Module metadata pointing to Kconfig |
Advanced Topics
Kconfig Functions
Integrate Kconfig with devicetree at build time.
- Functions reference (dt_chosen_enabled, dt_nodelabel_enabled, etc.): See functions.md
Practical Examples
Complete Kconfig patterns for common scenarios.
- Driver, subsystem, choice examples: See examples.md
Troubleshooting
For common errors and debugging techniques:
- See debugging.md
Quick Reference
| Error | Likely Cause | Fix |
|---|---|---|
| "X" has unmet dependencies | Missing depends on |
Enable required dependency first |
| Symbol not visible | depends on condition false |
Check what it depends on |
| Unknown symbol "X" | Typo or Kconfig not sourced | Verify spelling, check module.yml |
| warning: Y selected by X but not visible | select bypassing depends on |
Use imply or fix dependencies |
References
- syntax.md — Types, menus, choices, conditionals, sourcing
- best_practices.md — Naming, organization, modules, dependency safety
- menuconfig.md — Interactive configuration workflow
- functions.md — Kconfig functions for devicetree integration
- examples.md — Complete Kconfig patterns
- debugging.md — Error resolution and debugging techniques