The following page provides suggestions for common errors that may occur during firmware compilation or other issues with keyboard usage. If the information provided is insufficient to resolve the issue, feel free to seek out help from the [ZMK Discord](https://zmk.dev/community/discord/invite).
Variations of the warnings shown below occur when flashing the `<firmware>.uf2` onto the microcontroller. This is because the microcontroller resets itself before the OS receives confirmation that the file transfer is complete. Errors like this are normal and can generally be ignored. Verification of a functional board can be done by attempting to pair your newly flashed keyboard to your computer via Bluetooth or plugging in a USB cable if `ZMK_USB` is enabled in your Kconfig.defconfig.
An error along the lines of `CMake Error at (zmk directory)/zephyr/cmake/generic_toolchain.cmake:64 (include): include could not find load file:` during firmware compilation indicates that the Zephyr Environment Variables are not properly defined.
An error along the lines of `dtlib.DTError: <board>.dts.pre.tmp:<line number>` during firmware compilation indicates an issue within the `<shield>.keymap` file.
This can be verified by checking the file in question, found in `mkdir/app/build`.
After opening the `<board>.dts.pre.tmp:<line number>` and scrolling down to the referenced line, one can locate errors within their shield's keymap by checking if the referenced keycodes were properly converted into the correct [USB HID Usage ID](https://www.usb.org/document-library/hid-usage-tables-12).
| An incorrectly defined keymap unable to compile. As shown in red, `&kp SPAC` is not a valid reference to the [USB HID Usage ID](https://www.usb.org/document-library/hid-usage-tables-12) used for "Keyboard Spacebar" |
| A properly defined keymap with successful compilation. As shown in red, the corrected keycode (`&kp SPACE`) references the proper Usage ID defined in the [USB HID Usage Tables](https://www.usb.org/document-library/hid-usage-tables-12) |
Previously, pairing split keyboard halves involved a **BLE Reset** via a combination of held keys that removed all bluetooth profile information from the keyboard.
1. [Open the GitHub `Actions` tab and select the `Build` workflow](https://github.com/zmkfirmware/zmk/actions?query=workflow%3ABuild+branch%3Amain+event%3Apush).
1. Put each half of the split keyboard into bootloader mode
1. Flash one of the halves of the split with the "settings clear" UF2 image from step 1. Immediately after flashing "settings clear" to the chosen half, immediately put it into bootloader mode
After completing these steps, pair the halves of the split keyboard together by resetting them at the same time. Most commonly, this is done by grounding the reset pins
Some users may experience a poor connection between the keyboard and the host. This might be due to poor quality BLE hardware, a metal enclosure on the keyboard or host, or the distance between them. Increasing the transmit power of the keyboard's BLE radio may reduce the severity of this problem. To do this, set the `CONFIG_BT_CTLR_TX_PWR_PLUS_8` configuration value in the `.conf` file of your user config directory as such:
For the `nRF52840`, the value `PLUS_8` can be set to any multiple of four between `MINUS_20` and `PLUS_8`. The default value for this config is `0`, but if you are having connection issues it is recommended to set it to `PLUS_8` because the power consumption difference is negligible. For more information on changing the transmit power of your BLE device, please refer to [the Zephyr docs.](https://docs.zephyrproject.org/latest/reference/kconfig/CONFIG_BT_CTLR_TX_PWR_PLUS_8.html)
- If you want to test bluetooth output on your keyboard and are powering it through the USB connection rather than a battery, you will be able to pair with a host device but may not see keystrokes sent. In this case you need to use the [output selection behavior](../docs/behaviors/outputs.md) to prefer sending keystrokes over bluetooth rather than USB. This might be necessary even if you are not powering from a device capable of receiving USB inputs, such as a USB charger.
