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.
The following KConfig values need 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 various settings in that UI.
After flashing the updated ZMK image, the board should expose a USB CDC ACM device that you can connect to and view the logs.
On Linux, this should be a device like
/dev/ttyACM0 and you can connect with
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.