USB Logging
Overview
If you are developing ZMK on a device that does not have a built in UART for debugging and log/console output,
Zephyr can be configured to create a USB CDC ACM device and the direct all printk, console output, and log
messages to that device instead.
Battery Life Impact
Enabling logging increases the power usage of your keyboard, and can have a non-trivial impact to your time on battery. It is recommended to only enable logging when needed, and not leaving it on by default.
Kconfig
The CONFIG_ZMK_USB_LOGGING KConfig value needs to be set, either by copy and pasting into the app/prj.conf file, or by running
west build -t menuconfig and manually enabling the setting in that UI at ZMK -> Advanced -> USB Logging.
note
If you are debugging your own keyboard in your user config repository, use
config/boards/shields/<your_keyboard>/<your_keyboard>.conf instead of app/prj.conf. In Github
Actions, you can search the Kconfig file build log to verify the options above have been enabled
for you successfully.
Viewing Logs
After flashing the updated ZMK image, the board should expose a USB CDC ACM device that you can connect to and view the logs.
- Linux
- Windows
- MacOS
On Linux, this should be a device like /dev/ttyACM0 and you can connect with minicom or tio as usual, e.g.:
From there, you should see the various log messages from ZMK and Zephyr, depending on which systems you have set to what log levels.