2020-07-08 01:58:12 +10:00
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---
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id: dev-guide-usb-logging
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title: USB Logging
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---
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## Overview
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If you are developing ZMK on a device that does not have a built in UART for debugging and log/console output,
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Zephyr can be configured to create a USB CDC ACM device and the direct all `printk`, console output, and log
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messages to that device instead.
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## Kconfig
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The following KConfig values need to be set, either by copy and paste into the `app/prj.conf` file, or by running
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`west build -t menuconfig` and manually enabling the various settings in that UI.
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```
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# Turn on logging, and set ZMK logging to debug output
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CONFIG_LOG=y
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CONFIG_ZMK_LOG_LEVEL_DBG=y
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# Turn on USB CDC ACM device
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2020-08-06 12:59:58 +10:00
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CONFIG_USB=y
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CONFIG_USB_DEVICE_STACK=y
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2020-07-08 01:58:12 +10:00
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CONFIG_USB_CDC_ACM=y
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CONFIG_USB_CDC_ACM_RINGBUF_SIZE=1024
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CONFIG_USB_CDC_ACM_DEVICE_NAME="CDC_ACM"
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CONFIG_USB_CDC_ACM_DEVICE_COUNT=1
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# Enable serial console
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CONFIG_SERIAL=y
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CONFIG_CONSOLE=y
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CONFIG_UART_INTERRUPT_DRIVEN=y
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CONFIG_UART_LINE_CTRL=y
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# Enable USB UART, and set the console device
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CONFIG_UART_CONSOLE=y
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CONFIG_USB_UART_CONSOLE=y
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CONFIG_UART_CONSOLE_ON_DEV_NAME="CDC_ACM_0"
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CONFIG_USB_UART_DTR_WAIT=n
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```
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## Viewing Logs
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After flashing the updated ZMK image, the board should expose a USB CDC ACM device, that you can connect to and view the logs.
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On Linux, this should be a device like `/dev/ttyACM0` and you can connect with `minicom` or `tio` as usual, e.g.:
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```
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sudo tio /dev/ttyACM0
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```
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From there, you should see the various log messages from ZMK and Zephyr, depending on which systems you have set to what log levels.
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