System Configuration
These are general settings that control how the keyboard behaves and which features it supports. Several of these settings come from Zephyr and are not specific to ZMK, but they are listed here because they are relevant to how a keyboard functions.
See Configuration Overview for instructions on how to change these settings.
Kconfig
Definition file: zmk/app/Kconfig
General
| Config | Type | Description | Default |
|---|---|---|---|
CONFIG_ZMK_KEYBOARD_NAME | string | The name of the keyboard (max 16 characters) | |
CONFIG_ZMK_SETTINGS_RESET_ON_START | bool | Clears all persistent settings from the keyboard at startup | n |
CONFIG_ZMK_SETTINGS_SAVE_DEBOUNCE | int | Milliseconds to wait after a setting change before writing it to flash memory | 60000 |
CONFIG_ZMK_WPM | bool | Enable calculating words per minute | n |
CONFIG_HEAP_MEM_POOL_SIZE | int | Size of the heap memory pool | 8192 |
HID
Making changes to any of the settings in this section modifies the HID report descriptor and requires it to be refreshed.
| Config | Type | Description | Default |
|---|---|---|---|
CONFIG_ZMK_HID_INDICATORS | bool | Enable receipt of HID/LED indicator state from connected hosts | n |
CONFIG_ZMK_HID_CONSUMER_REPORT_SIZE | int | Number of consumer keys simultaneously reportable | 6 |
CONFIG_ZMK_HID_SEPARATE_MOD_RELEASE_REPORT | bool | Send modifier release event after non-modifier release event | n |
Exactly zero or one of the following options may be set to y. The first is used if none are set.
| Config | Description |
|---|---|
CONFIG_ZMK_HID_REPORT_TYPE_HKRO | Enable CONFIG_ZMK_HID_KEYBOARD_REPORT_SIZE key roll over. |
CONFIG_ZMK_HID_REPORT_TYPE_NKRO | Enable full N-key roll over. This may prevent the keyboard from working with some BIOS/UEFI versions. |
By default the NKRO max usage is set so as to maximize compatibility, however certain less frequently used keys (F13-F24 and INTL1-8) will not work with it. One solution is to set CONFIG_ZMK_HID_KEYBOARD_NKRO_EXTENDED_REPORT=y, however this is known to break compatibility with Android and thus not enabled by default.
If CONFIG_ZMK_HID_REPORT_TYPE_HKRO is enabled, it may be configured with the following options:
| Config | Type | Description | Default |
|---|---|---|---|
CONFIG_ZMK_HID_KEYBOARD_REPORT_SIZE | int | Number of keyboard keys simultaneously reportable | 6 |
If CONFIG_ZMK_HID_REPORT_TYPE_NKRO is enabled, it may be configured with the following options:
| Config | Type | Description | Default |
|---|---|---|---|
CONFIG_ZMK_HID_KEYBOARD_NKRO_EXTENDED_REPORT | bool | Enable less frequently used key usages, at the cost of compatibility | n |
Exactly zero or one of the following options may be set to y. The first is used if none are set.
| Config | Description |
|---|---|
CONFIG_ZMK_HID_CONSUMER_REPORT_USAGES_FULL | Enable all consumer key codes, but may have compatibility issues with some host OSes |
CONFIG_ZMK_HID_CONSUMER_REPORT_USAGES_BASIC | Prevents using some consumer key codes, but allows compatibility with more host OSes |
USB
| Config | Type | Description | Default |
|---|---|---|---|
CONFIG_USB | bool | Enable USB drivers | |
CONFIG_USB_DEVICE_VID | int | The vendor ID advertised to USB | 0x1D50 |
CONFIG_USB_DEVICE_PID | int | The product ID advertised to USB | 0x615E |
CONFIG_USB_DEVICE_MANUFACTURER | string | The manufacturer name advertised to USB | "ZMK Project" |
CONFIG_USB_HID_POLL_INTERVAL_MS | int | USB polling interval in milliseconds | 1 |
CONFIG_ZMK_USB | bool | Enable ZMK as a USB keyboard | |
CONFIG_ZMK_USB_BOOT | bool | Enable USB Boot protocol support | n |
CONFIG_ZMK_USB_INIT_PRIORITY | int | USB init priority | 50 |
By default USB Boot protocol support is disabled, however certain situations such as the input of Bitlocker pins or FileVault passwords may require it to be enabled.
Bluetooth
See Zephyr's Bluetooth stack architecture documentation for more information on configuring Bluetooth.
| Config | Type | Description | Default |
|---|---|---|---|
CONFIG_BT | bool | Enable Bluetooth support | |
CONFIG_BT_BAS | bool | Enable the Bluetooth BAS (battery reporting service) | y |
CONFIG_BT_MAX_CONN | int | Maximum number of simultaneous Bluetooth connections | 5 |
CONFIG_BT_MAX_PAIRED | int | Maximum number of paired Bluetooth devices | 5 |
CONFIG_ZMK_BLE | bool | Enable ZMK as a Bluetooth keyboard | |
CONFIG_ZMK_BLE_CLEAR_BONDS_ON_START | bool | Clears all bond information from the keyboard on startup | n |
CONFIG_ZMK_BLE_CONSUMER_REPORT_QUEUE_SIZE | int | Max number of consumer HID reports to queue for sending over BLE | 5 |
CONFIG_ZMK_BLE_KEYBOARD_REPORT_QUEUE_SIZE | int | Max number of keyboard HID reports to queue for sending over BLE | 20 |
CONFIG_ZMK_BLE_INIT_PRIORITY | int | BLE init priority | 50 |
CONFIG_ZMK_BLE_THREAD_PRIORITY | int | Priority of the BLE notify thread | 5 |
CONFIG_ZMK_BLE_THREAD_STACK_SIZE | int | Stack size of the BLE notify thread | 512 |
CONFIG_ZMK_BLE_PASSKEY_ENTRY | bool | Experimental: require typing passkey from host to pair BLE connection | n |
Note that CONFIG_BT_MAX_CONN and CONFIG_BT_MAX_PAIRED should be set to the same value. On a split keyboard they should only be set for the central and must be set to one greater than the desired number of bluetooth profiles.
Logging
| Config | Type | Description | Default |
|---|---|---|---|
CONFIG_ZMK_USB_LOGGING | bool | Enable USB CDC ACM logging for debugging | n |
CONFIG_ZMK_LOG_LEVEL | int | Log level for ZMK debug messages | 4 |
Split keyboards
Following split keyboard settings are defined in zmk/app/src/split/Kconfig (generic) and zmk/app/src/split/bluetooth/Kconfig (bluetooth).
| Config | Type | Description | Default |
|---|---|---|---|
CONFIG_ZMK_SPLIT | bool | Enable split keyboard support | n |
CONFIG_ZMK_SPLIT_ROLE_CENTRAL | bool | y for central device, n for peripheral | |
CONFIG_ZMK_SPLIT_PERIPHERAL_HID_INDICATORS | bool | Enable split keyboard support for passing indicator state to peripherals | n |
CONFIG_ZMK_SPLIT_BLE | bool | Use BLE to communicate between split keyboard halves | y |
CONFIG_ZMK_SPLIT_BLE_CENTRAL_PERIPHERALS | int | Number of peripherals that will connect to the central | 1 |
CONFIG_ZMK_SPLIT_BLE_CENTRAL_BATTERY_LEVEL_FETCHING | bool | Enable fetching split peripheral battery levels to the central side | n |
CONFIG_ZMK_SPLIT_BLE_CENTRAL_BATTERY_LEVEL_PROXY | bool | Enable central reporting of split battery levels to hosts | n |
CONFIG_ZMK_SPLIT_BLE_CENTRAL_BATTERY_LEVEL_QUEUE_SIZE | int | Max number of battery level events to queue when received from peripherals | CONFIG_ZMK_SPLIT_BLE_CENTRAL_PERIPHERALS |
CONFIG_ZMK_SPLIT_BLE_CENTRAL_POSITION_QUEUE_SIZE | int | Max number of key state events to queue when received from peripherals | 5 |
CONFIG_ZMK_SPLIT_BLE_CENTRAL_SPLIT_RUN_STACK_SIZE | int | Stack size of the BLE split central write thread | 512 |
CONFIG_ZMK_SPLIT_BLE_CENTRAL_SPLIT_RUN_QUEUE_SIZE | int | Max number of behavior run events to queue to send to the peripheral(s) | 5 |
CONFIG_ZMK_SPLIT_BLE_PERIPHERAL_STACK_SIZE | int | Stack size of the BLE split peripheral notify thread | 650 |
CONFIG_ZMK_SPLIT_BLE_PERIPHERAL_PRIORITY | int | Priority of the BLE split peripheral notify thread | 5 |
CONFIG_ZMK_SPLIT_BLE_PERIPHERAL_POSITION_QUEUE_SIZE | int | Max number of key state events to queue to send to the central | 10 |
Snippets
Using these snippets can erase the SoftDevice on your board. Erasing the SoftDevice will prevent the board from using firmware built without these snippets.
Flashing such firmware will totally brick the board, disabling the USB flashing functionality. The only way to restore functionality after that is to re-flash the bootloader.
Re-flashing a bootloader built without the SoftDevice will require firmware built with these snippets.
Snippets are a way to save common configuration separately when it applies to multiple different applications.
Enable snippets by adding snippet: <snippet> to your build.yaml for the appropriate board:
- board: nrfmicro_13_52833
snippet: nrf52833-nosd
shield: corne_left
For local builds, add -S <snippet> to your build command. For example:
west build -b nrfmicro_13_52833 -S nrf52833-nosd -- -DSHIELD=corne_left
ZMK implements the following system configuration snippets:
nrf52833-nosd
Definition: zmk/app/snippets/nrf52833-nosd
On memory-constrained nRF52833 boards this snippet will extend the code partition to overwrite the Nordic SoftDevice. This gives 428KB for the code partition as opposed to 280KB with the Nordic SoftDevice.
The added memory allows the nRF52833 to fit displays and other memory-intensive features.
nrf52840-nosd
Definition: zmk/app/snippets/nrf52840-nosd
On nRF52840 boards this snippet will overwrite the Nordic SoftDevice, extending both the code and storage partitions. This gives 844KB/128KB for the code/storage partitions as opposed to 792KB/32KB with the Nordic SoftDevice.
Firmware built with this snippet can work on boards after accidentally erasing the SoftDevice. It can also be useful for especially memory-intensive applications.