24 KiB
Configuring QMK
QMK is nearly infinitely configurable. Wherever possible we err on the side of allowing users to customize their keyboard, even at the expense of code size. That level of flexibility makes for a daunting configuration experience, however.
There are three main types of configuration files in QMK:
config.h
, which contains various preprocessor directives (#define
,#ifdef
)rules.mk
, which contains additional variablesinfo.json
, which is utilized for data-driven configuration
This page will only discuss the first two types, config.h
and rules.mk
.
?> While not all settings have data-driven equivalents yet, keyboard makers are encouraged to utilize the info.json
file to set the metadata for their boards when possible. See the info.json
Format page for more details.
These files exist at various levels in QMK and all files of the same type are combined to build the final configuration. The levels, from lowest priority to highest priority, are:
- QMK Default
- Keyboard
- Folders (Up to 5 levels deep)
- Keymap
QMK Default
Every available setting in QMK has a default. If that setting is not set at the Keyboard, Folder, or Keymap level this is the setting that will be used.
Keyboard
This level contains config options that should apply to the whole keyboard. Some settings won't change in revisions, or most keymaps. Other settings are merely defaults for this keyboard and can be overridden by folders and/or keymaps.
Folders
Some keyboards have folders and sub-folders to allow for different hardware configurations. Most keyboards only go 1 folder deep, but QMK supports structures up to 5 folders deep. Each folder can have its own config.h
and rules.mk
files that are incorporated into the final configuration.
Keymap
This level contains all of the options for that particular keymap. If you wish to override a previous declaration, you can use #undef <variable>
to undefine it, where you can then redefine it without an error.
The config.h
File
This is a C header file that is one of the first things included, and will persist over the whole project (if included). Lots of variables can be set here and accessed elsewhere. The config.h
file shouldn't be including other config.h
files, or anything besides this:
#include "config_common.h"
Hardware Options
#define VENDOR_ID 0x1234
- defines your VID, and for most DIY projects, can be whatever you want
#define PRODUCT_ID 0x5678
- defines your PID, and for most DIY projects, can be whatever you want
#define DEVICE_VER 0x0100
- defines the device version (often used for revisions)
#define MANUFACTURER "Me"
- generally who/whatever brand produced the board
#define PRODUCT "Board"
- the name of the keyboard
#define MATRIX_ROWS 5
- the number of rows in your keyboard's matrix
#define MATRIX_COLS 15
- the number of columns in your keyboard's matrix
#define MATRIX_ROW_PINS { D0, D5, B5, B6 }
- pins of the rows, from top to bottom
- may be omitted by the keyboard designer if matrix reads are handled in an alternate manner. See low-level matrix overrides for more information.
#define MATRIX_COL_PINS { F1, F0, B0, C7, F4, F5, F6, F7, D4, D6, B4, D7 }
- pins of the columns, from left to right
- may be omitted by the keyboard designer if matrix reads are handled in an alternate manner. See low-level matrix overrides for more information.
#define MATRIX_IO_DELAY 30
- the delay in microseconds when between changing matrix pin state and reading values
#define MATRIX_HAS_GHOST
- define is matrix has ghost (unlikely)
#define MATRIX_UNSELECT_DRIVE_HIGH
- On un-select of matrix pins, rather than setting pins to input-high, sets them to output-high.
#define DIODE_DIRECTION COL2ROW
- COL2ROW or ROW2COL - how your matrix is configured. COL2ROW means the black mark on your diode is facing to the rows, and between the switch and the rows.
#define DIRECT_PINS { { F1, F0, B0, C7 }, { F4, F5, F6, F7 } }
- pins mapped to rows and columns, from left to right. Defines a matrix where each switch is connected to a separate pin and ground.
#define AUDIO_VOICES
- turns on the alternate audio voices (to cycle through)
#define C4_AUDIO
- enables audio on pin C4
- Deprecated. Use
#define AUDIO_PIN C4
#define C5_AUDIO
- enables audio on pin C5
- Deprecated. Use
#define AUDIO_PIN C5
#define C6_AUDIO
- enables audio on pin C6
- Deprecated. Use
#define AUDIO_PIN C6
#define B5_AUDIO
- enables audio on pin B5 (duophony is enabled if one of B pins is enabled along with one of C pins)
- Deprecated. Use
#define AUDIO_PIN B5
, or use#define AUDIO_PIN_ALT B5
if aC
pin is enabled withAUDIO_PIN
#define B6_AUDIO
- enables audio on pin B6 (duophony is enabled if one of B pins is enabled along with one of C pins)
- Deprecated. Use
#define AUDIO_PIN B6
, or use#define AUDIO_PIN_ALT B6
if aC
pin is enabled withAUDIO_PIN
#define B7_AUDIO
- enables audio on pin B7 (duophony is enabled if one of B pins is enabled along with one of C pins)
- Deprecated. Use
#define AUDIO_PIN B7
, or use#define AUDIO_PIN_ALT B7
if aC
pin is enabled withAUDIO_PIN
#define BACKLIGHT_PIN B7
- pin of the backlight
#define BACKLIGHT_LEVELS 3
- number of levels your backlight will have (maximum 31 excluding off)
#define BACKLIGHT_BREATHING
- enables backlight breathing
#define BREATHING_PERIOD 6
- the length of one backlight "breath" in seconds
#define DEBOUNCE 5
- the delay when reading the value of the pin (5 is default)
#define LOCKING_SUPPORT_ENABLE
- mechanical locking support. Use KC_LCAP, KC_LNUM or KC_LSCR instead in keymap
#define LOCKING_RESYNC_ENABLE
- tries to keep switch state consistent with keyboard LED state
#define IS_COMMAND() (get_mods() == MOD_MASK_SHIFT)
- key combination that allows the use of magic commands (useful for debugging)
#define USB_MAX_POWER_CONSUMPTION 500
- sets the maximum power (in mA) over USB for the device (default: 500)
#define USB_POLLING_INTERVAL_MS 10
- sets the USB polling rate in milliseconds for the keyboard, mouse, and shared (NKRO/media keys) interfaces
#define USB_SUSPEND_WAKEUP_DELAY 0
- sets the number of milliseconds to pause after sending a wakeup packet. Disabled by default, you might want to set this to 200 (or higher) if the keyboard does not wake up properly after suspending.
#define F_SCL 100000L
- sets the I2C clock rate speed for keyboards using I2C. The default is
400000L
, except for keyboards usingsplit_common
, where the default is100000L
.
- sets the I2C clock rate speed for keyboards using I2C. The default is
Features That Can Be Disabled
If you define these options you will disable the associated feature, which can save on code size.
#define NO_DEBUG
- disable debugging
#define NO_PRINT
- disable printing/debugging using hid_listen
#define NO_ACTION_LAYER
- disable layers
#define NO_ACTION_TAPPING
- disable tap dance and other tapping features
#define NO_ACTION_ONESHOT
- disable one-shot modifiers
Features That Can Be Enabled
If you define these options you will enable the associated feature, which may increase your code size.
#define ENABLE_COMPILE_KEYCODE
- Enables the
QK_MAKE
keycode
- Enables the
#define FORCE_NKRO
- NKRO by default requires to be turned on, this forces it on during keyboard startup regardless of EEPROM setting. NKRO can still be turned off but will be turned on again if the keyboard reboots.
#define STRICT_LAYER_RELEASE
- force a key release to be evaluated using the current layer stack instead of remembering which layer it came from (used for advanced cases)
Behaviors That Can Be Configured
#define TAPPING_TERM 200
- how long before a key press becomes a hold
#define TAPPING_TERM_PER_KEY
- enables handling for per key
TAPPING_TERM
settings
- enables handling for per key
#define RETRO_TAPPING
- tap anyway, even after TAPPING_TERM, if there was no other key interruption between press and release
- See Retro Tapping for details
#define RETRO_TAPPING_PER_KEY
- enables handling for per key
RETRO_TAPPING
settings
- enables handling for per key
#define TAPPING_TOGGLE 2
- how many taps before triggering the toggle
#define PERMISSIVE_HOLD
- makes tap and hold keys trigger the hold if another key is pressed before releasing, even if it hasn't hit the
TAPPING_TERM
- See Permissive Hold for details
- makes tap and hold keys trigger the hold if another key is pressed before releasing, even if it hasn't hit the
#define PERMISSIVE_HOLD_PER_KEY
- enabled handling for per key
PERMISSIVE_HOLD
settings
- enabled handling for per key
#define IGNORE_MOD_TAP_INTERRUPT
- makes it possible to do rolling combos (zx) with keys that convert to other keys on hold, by enforcing the
TAPPING_TERM
for both keys. - See Ignore Mod Tap Interrupt for details
- makes it possible to do rolling combos (zx) with keys that convert to other keys on hold, by enforcing the
#define IGNORE_MOD_TAP_INTERRUPT_PER_KEY
- enables handling for per key
IGNORE_MOD_TAP_INTERRUPT
settings
- enables handling for per key
#define TAPPING_FORCE_HOLD
- makes it possible to use a dual role key as modifier shortly after having been tapped
- See Tapping Force Hold
- Breaks any Tap Toggle functionality (
TT
or the One Shot Tap Toggle)
#define TAPPING_FORCE_HOLD_PER_KEY
- enables handling for per key
TAPPING_FORCE_HOLD
settings
- enables handling for per key
#define LEADER_TIMEOUT 300
- how long before the leader key times out
- If you're having issues finishing the sequence before it times out, you may need to increase the timeout setting. Or you may want to enable the
LEADER_PER_KEY_TIMING
option, which resets the timeout after each key is tapped.
- If you're having issues finishing the sequence before it times out, you may need to increase the timeout setting. Or you may want to enable the
- how long before the leader key times out
#define LEADER_PER_KEY_TIMING
- sets the timer for leader key chords to run on each key press rather than overall
#define LEADER_KEY_STRICT_KEY_PROCESSING
- Disables keycode filtering for Mod-Tap and Layer-Tap keycodes. Eg, if you enable this, you would need to specify
MT(MOD_CTL, KC_A)
if you want to useKC_A
.
- Disables keycode filtering for Mod-Tap and Layer-Tap keycodes. Eg, if you enable this, you would need to specify
#define MOUSE_EXTENDED_REPORT
- Enables support for extended reports (-32767 to 32767, instead of -127 to 127), which may allow for smoother reporting, and prevent maxing out of the reports. Applies to both Pointing Device and Mousekeys.
#define ONESHOT_TIMEOUT 300
- how long before oneshot times out
#define ONESHOT_TAP_TOGGLE 2
- how many taps before oneshot toggle is triggered
#define COMBO_COUNT 2
- Set this to the number of combos that you're using in the Combo feature. Or leave it undefined and programmatically set the count.
#define COMBO_TERM 200
- how long for the Combo keys to be detected. Defaults to
TAPPING_TERM
if not defined.
- how long for the Combo keys to be detected. Defaults to
#define COMBO_MUST_HOLD_MODS
- Flag for enabling extending timeout on Combos containing modifiers
#define COMBO_MOD_TERM 200
- Allows for extending COMBO_TERM for mod keys while mid-combo.
#define COMBO_MUST_HOLD_PER_COMBO
- Flag to enable per-combo COMBO_TERM extension and
get_combo_must_hold()
function
- Flag to enable per-combo COMBO_TERM extension and
#define COMBO_TERM_PER_COMBO
- Flag to enable per-combo COMBO_TERM extension and
get_combo_term()
function
- Flag to enable per-combo COMBO_TERM extension and
#define COMBO_STRICT_TIMER
- Only start the combo timer on the first key press instead of on all key presses.
#define COMBO_NO_TIMER
- Disable the combo timer completely for relaxed combos.
#define TAP_CODE_DELAY 100
- Sets the delay between
register_code
andunregister_code
, if you're having issues with it registering properly (common on VUSB boards). The value is in milliseconds.
- Sets the delay between
#define TAP_HOLD_CAPS_DELAY 80
- Sets the delay for Tap Hold keys (
LT
,MT
) when usingKC_CAPS_LOCK
keycode, as this has some special handling on MacOS. The value is in milliseconds, and defaults to 80 ms if not defined. For macOS, you may want to set this to 200 or higher.
- Sets the delay for Tap Hold keys (
#define KEY_OVERRIDE_REPEAT_DELAY 500
- Sets the key repeat interval for key overrides.
RGB Light Configuration
#define RGB_DI_PIN D7
- pin the DI on the WS2812 is hooked-up to
#define RGBLIGHT_LAYERS
- Lets you define lighting layers that can be toggled on or off. Great for showing the current keyboard layer or caps lock state.
#define RGBLIGHT_MAX_LAYERS
- Defaults to 8. Can be expanded up to 32 if more lighting layers are needed.
- Note: Increasing the maximum will increase the firmware size and slow sync on split keyboards.
#define RGBLIGHT_LAYER_BLINK
- Adds ability to blink a lighting layer for a specified number of milliseconds (e.g. to acknowledge an action).
#define RGBLIGHT_LAYERS_OVERRIDE_RGB_OFF
- If defined, then lighting layers will be shown even if RGB Light is off.
#define RGBLED_NUM 12
- number of LEDs
#define RGBLIGHT_SPLIT
- Needed if both halves of the board have RGB LEDs wired directly to the RGB output pin on the controllers instead of passing the output of the left half to the input of the right half
#define RGBLED_SPLIT { 6, 6 }
- number of LEDs connected that are directly wired to
RGB_DI_PIN
on each half of a split keyboard - First value indicates number of LEDs for left half, second value is for the right half
- When RGBLED_SPLIT is defined, RGBLIGHT_SPLIT is implicitly defined.
- number of LEDs connected that are directly wired to
#define RGBLIGHT_HUE_STEP 12
- units to step when in/decreasing hue
#define RGBLIGHT_SAT_STEP 25
- units to step when in/decreasing saturation
#define RGBLIGHT_VAL_STEP 12
- units to step when in/decreasing value (brightness)
#define RGBW
- Enables RGBW LED support
Mouse Key Options
#define MOUSEKEY_INTERVAL 20
#define MOUSEKEY_DELAY 0
#define MOUSEKEY_TIME_TO_MAX 60
#define MOUSEKEY_MAX_SPEED 7
#define MOUSEKEY_WHEEL_DELAY 0
Split Keyboard Options
Split Keyboard specific options, make sure you have 'SPLIT_KEYBOARD = yes' in your rules.mk
SPLIT_TRANSPORT = custom
- Allows replacing the standard split communication routines with a custom one. ARM based split keyboards must use this at present.
Setting Handedness
One thing to remember, the side that the USB port is plugged into is always the master half. The side not plugged into USB is the slave.
There are a few different ways to set handedness for split keyboards (listed in order of precedence):
- Set
SPLIT_HAND_PIN
: Reads a pin to determine handedness. If pin is high, it's the left side, if low, the half is determined to be the right side - Set
EE_HANDS
and flasheeprom-lefthand.eep
/eeprom-righthand.eep
to each half- For boards with DFU bootloader you can use
:dfu-split-left
/:dfu-split-right
to flash these EEPROM files - For boards with Caterina bootloader (like stock Pro Micros), use
:avrdude-split-left
/:avrdude-split-right
- For boards with ARM DFU bootloader (like Proton C), use
:dfu-util-split-left
/:dfu-util-split-right
- For boards with DFU bootloader you can use
- Set
MASTER_RIGHT
: Half that is plugged into the USB port is determined to be the master and right half (inverse of the default) - Default: The side that is plugged into the USB port is the master half and is assumed to be the left half. The slave side is the right half
Defines for handedness
-
#define SPLIT_HAND_PIN B7
- For using high/low pin to determine handedness, low = right hand, high = left hand. Replace
B7
with the pin you are using. This is optional, and if you leaveSPLIT_HAND_PIN
undefined, then you can still use the EE_HANDS method or MASTER_LEFT / MASTER_RIGHT defines like the stock Let's Split uses.
- For using high/low pin to determine handedness, low = right hand, high = left hand. Replace
-
#define SPLIT_HAND_MATRIX_GRID <out_pin>,<in_pin>
- The handedness is determined by using the intersection of the keyswitches in the key matrix, which does not exist. Normally, when this intersection is shorted (level low), it is considered left. If you define
#define SPLIT_HAND_MATRIX_GRID_LOW_IS_RIGHT
, it is determined to be right when the level is low.
- The handedness is determined by using the intersection of the keyswitches in the key matrix, which does not exist. Normally, when this intersection is shorted (level low), it is considered left. If you define
-
#define EE_HANDS
(only works ifSPLIT_HAND_PIN
andSPLIT_HAND_MATRIX_GRID
are not defined)- Reads the handedness value stored in the EEPROM after
eeprom-lefthand.eep
/eeprom-righthand.eep
has been flashed to their respective halves.
- Reads the handedness value stored in the EEPROM after
-
#define MASTER_RIGHT
- Master half is defined to be the right half.
Other Options
-
#define USE_I2C
- For using I2C instead of Serial (default is serial; serial transport is supported on ARM -- I2C is AVR-only)
-
#define SOFT_SERIAL_PIN D0
- When using serial, define this.
D0
orD1
,D2
,D3
,E6
.
- When using serial, define this.
-
#define MATRIX_ROW_PINS_RIGHT { <row pins> }
-
#define MATRIX_COL_PINS_RIGHT { <col pins> }
- If you want to specify a different pinout for the right half than the left half, you can define
MATRIX_ROW_PINS_RIGHT
/MATRIX_COL_PINS_RIGHT
. Currently, the size ofMATRIX_ROW_PINS
must be the same asMATRIX_ROW_PINS_RIGHT
and likewise for the definition of columns. - may be omitted by the keyboard designer if matrix reads are handled in an alternate manner. See low-level matrix overrides for more information.
- If you want to specify a different pinout for the right half than the left half, you can define
-
#define DIRECT_PINS_RIGHT { { F1, F0, B0, C7 }, { F4, F5, F6, F7 } }
- If you want to specify a different direct pinout for the right half than the left half, you can define
DIRECT_PINS_RIGHT
. Currently, the size ofDIRECT_PINS
must be the same asDIRECT_PINS_RIGHT
.
- If you want to specify a different direct pinout for the right half than the left half, you can define
-
#define RGBLED_SPLIT { 6, 6 }
-
#define SELECT_SOFT_SERIAL_SPEED <speed>
(default speed is 1)- Sets the protocol speed when using serial communication
- Speeds:
- 0: about 189kbps (Experimental only)
- 1: about 137kbps (default)
- 2: about 75kbps
- 3: about 39kbps
- 4: about 26kbps
- 5: about 20kbps
-
#define SPLIT_USB_DETECT
- Detect (with timeout) USB connection when delegating master/slave
- Default behavior for ARM
- Required for AVR Teensy (without hardware mods)
-
#define SPLIT_USB_TIMEOUT 2000
- Maximum timeout when detecting master/slave when using
SPLIT_USB_DETECT
- Maximum timeout when detecting master/slave when using
-
#define SPLIT_USB_TIMEOUT_POLL 10
- Poll frequency when detecting master/slave when using
SPLIT_USB_DETECT
- Poll frequency when detecting master/slave when using
-
#define FORCED_SYNC_THROTTLE_MS 100
- Deadline for synchronizing data from master to slave when using the QMK-provided split transport.
-
#define SPLIT_TRANSPORT_MIRROR
- Mirrors the master-side matrix on the slave when using the QMK-provided split transport.
-
#define SPLIT_LAYER_STATE_ENABLE
- Ensures the current layer state is available on the slave when using the QMK-provided split transport.
-
#define SPLIT_LED_STATE_ENABLE
- Ensures the current host indicator state (caps/num/scroll) is available on the slave when using the QMK-provided split transport.
-
#define SPLIT_MODS_ENABLE
- Ensures the current modifier state (normal, weak, and oneshot) is available on the slave when using the QMK-provided split transport.
-
#define SPLIT_WPM_ENABLE
- Ensures the current WPM is available on the slave when using the QMK-provided split transport.
-
#define SPLIT_OLED_ENABLE
- Syncs the on/off state of the OLED between the halves.
-
#define SPLIT_ST7565_ENABLE
- Syncs the on/off state of the ST7565 screen between the halves.
-
#define SPLIT_TRANSACTION_IDS_KB .....
-
#define SPLIT_TRANSACTION_IDS_USER .....
- Allows for custom data sync with the slave when using the QMK-provided split transport. See custom data sync between sides for more information.
The rules.mk
File
This is a make file that is included by the top-level Makefile
. It is used to set some information about the MCU that we will be compiling for as well as enabling and disabling certain features.
Build Options
DEFAULT_FOLDER
- Used to specify a default folder when a keyboard has more than one sub-folder.
FIRMWARE_FORMAT
- Defines which format (bin, hex) is copied to the root
qmk_firmware
folder after building.
- Defines which format (bin, hex) is copied to the root
SRC
- Used to add files to the compilation/linking list.
LIB_SRC
- Used to add files as a library to the compilation/linking list.
The files specified by
LIB_SRC
is linked after the files specified bySRC
. For example, if you specify:
The link order is as follows.SRC += a.c LIB_SRC += lib_b.c SRC += c.c LIB_SRC += lib_d.c
... a.o c.o ... lib_b.a lib_d.a ...
- Used to add files as a library to the compilation/linking list.
The files specified by
LAYOUTS
- A list of layouts this keyboard supports.
LTO_ENABLE
- Enables Link Time Optimization (LTO) when compiling the keyboard. This makes the process take longer, but it can significantly reduce the compiled size (and since the firmware is small, the added time is not noticeable).
AVR MCU Options
MCU = atmega32u4
F_CPU = 16000000
ARCH = AVR8
F_USB = $(F_CPU)
OPT_DEFS += -DINTERRUPT_CONTROL_ENDPOINT
BOOTLOADER = atmel-dfu
with the following options:atmel-dfu
lufa-dfu
qmk-dfu
halfkay
caterina
bootloadhid
usbasploader
Feature Options :id=feature-options
Use these to enable or disable building certain features. The more you have enabled the bigger your firmware will be, and you run the risk of building a firmware too large for your MCU.
MAGIC_ENABLE
- MAGIC actions (BOOTMAGIC without the boot)
BOOTMAGIC_ENABLE
- Enable Bootmagic Lite
MOUSEKEY_ENABLE
- Mouse keys
EXTRAKEY_ENABLE
- Audio control and System control
CONSOLE_ENABLE
- Console for debug
COMMAND_ENABLE
- Commands for debug and configuration
COMBO_ENABLE
- Key combo feature
NKRO_ENABLE
- USB N-Key Rollover - if this doesn't work, see here: https://github.com/tmk/tmk_keyboard/wiki/FAQ#nkro-doesnt-work
RING_BUFFERED_6KRO_REPORT_ENABLE
- USB 6-Key Rollover - Instead of stopping any new input once 6 keys are pressed, the oldest key is released and the new key is pressed.
AUDIO_ENABLE
- Enable the audio subsystem.
KEY_OVERRIDE_ENABLE
- Enable the key override feature
RGBLIGHT_ENABLE
- Enable keyboard underlight functionality
LEADER_ENABLE
- Enable leader key chording
MIDI_ENABLE
- MIDI controls
UNICODE_ENABLE
- Unicode
BLUETOOTH_ENABLE
- Current options are BluefruitLE, RN42
SPLIT_KEYBOARD
- Enables split keyboard support (dual MCU like the let's split and bakingpy's boards) and includes all necessary files located at quantum/split_common
CUSTOM_MATRIX
- Allows replacing the standard matrix scanning routine with a custom one.
DEBOUNCE_TYPE
- Allows replacing the standard key debouncing routine with an alternative or custom one.
WAIT_FOR_USB
- Forces the keyboard to wait for a USB connection to be established before it starts up
NO_USB_STARTUP_CHECK
- Disables usb suspend check after keyboard startup. Usually the keyboard waits for the host to wake it up before any tasks are performed. This is useful for split keyboards as one half will not get a wakeup call but must send commands to the master.
DEFERRED_EXEC_ENABLE
- Enables deferred executor support -- timed delays before callbacks are invoked. See deferred execution for more information.
DYNAMIC_TAPPING_TERM_ENABLE
- Allows to configure the global tapping term on the fly.
USB Endpoint Limitations
In order to provide services over USB, QMK has to use USB endpoints. These are a finite resource: each microcontroller has only a certain number. This limits what features can be enabled together. If the available endpoints are exceeded, a build error is thrown.
The following features can require separate endpoints:
MOUSEKEY_ENABLE
EXTRAKEY_ENABLE
CONSOLE_ENABLE
NKRO_ENABLE
MIDI_ENABLE
RAW_ENABLE
VIRTSER_ENABLE
In order to improve utilisation of the endpoints, the HID features can be combined to use a single endpoint.
By default, MOUSEKEY
, EXTRAKEY
, and NKRO
are combined into a single endpoint.
The base keyboard functionality can also be combined into the endpoint,
by setting KEYBOARD_SHARED_EP = yes
.
This frees up one more endpoint,
but it can prevent the keyboard working in some BIOSes,
as they do not implement Boot Keyboard protocol switching.
Combining the mouse also breaks Boot Mouse compatibility.
The mouse can be uncombined by setting MOUSE_SHARED_EP = no
if this functionality is required.