---
title: System Configuration
sidebar_label: System
---

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](index.md) for instructions on how to change these settings.

## Kconfig

Definition file: [zmk/app/Kconfig](https://github.com/zmkfirmware/zmk/blob/main/app/Kconfig)

### General

| Config                              | Type   | Description                                                                   | Default |
| ----------------------------------- | ------ | ----------------------------------------------------------------------------- | ------- |
| `CONFIG_ZMK_KEYBOARD_NAME`          | string | The name of the keyboard (max 16 characters)                                  |         |
| `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

| Config                                | Type | Description                                                    | Default |
| ------------------------------------- | ---- | -------------------------------------------------------------- | ------- |
| `CONFIG_ZMK_HID_INDICATORS`           | bool | Enable reciept of HID/LED indicator state from connected hosts | n       |
| `CONFIG_ZMK_HID_CONSUMER_REPORT_SIZE` | int  | Number of consumer keys simultaneously reportable              | 6       |

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. |

:::note NKRO usages

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              |

:::note USB Boot protocol support

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](https://docs.zephyrproject.org/latest/guides/bluetooth/bluetooth-arch.html)
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](https://github.com/zmkfirmware/zmk/blob/main/app/src/split/Kconfig) (generic) and [zmk/app/src/split/Kconfig](https://github.com/zmkfirmware/zmk/blob/main/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_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                                         |
