Frequently Asked Questions

What is QMK?

QMK, short for Quantum Mechanical Keyboard, is a group of people building tools for custom keyboards. We started with the QMK firmware, a heavily modified fork of TMK.

What Differences Are There Between QMK and TMK?

TMK was originally designed and implemented by Jun Wako. QMK started as Jack Humbert's fork of TMK for the Planck. After a while Jack's fork had diverged quite a bit from TMK, and in 2015 Jack decided to rename his fork to QMK.

From a technical standpoint QMK builds upon TMK by adding several new features. Most notably QMK has expanded the number of available keycodes and uses these to implement advanced features like S(), LCTL(), and MO(). You can see a complete list of these keycodes in Quantum Keycodes.

From a project and community management standpoint TMK maintains all the officially supported keyboards by himself, with a bit of community support. Separate community maintained forks exist or can be created for other keyboards. Only a few keymaps are provided by default, so users typically don't share keymaps with each other. QMK encourages sharing of both keyboards and keymaps through a centrally managed repository, accepting all pull requests that follows the quality standards. These are mostly community maintained, but the QMK team also helps when necessary.

Both approaches have their merits and their drawbacks, and code flows freely between TMK and QMK when it makes sense.

Debug Console

hid_listen can't recognize device

When debug console of your device is not ready you will see like this:

Waiting for device:.........

once the device is pluged in then hid_listen finds it you will get this message:

Waiting for new device:.........................

If you can't get this 'Listening:' message try building with CONSOLE_ENABLE=yes in [Makefile]

You may need privilege to access the device on OS like Linux.

  • try sudo hid_listen

Can't get message on console


  • hid_listen finds your device. See above.
  • Enable debug with pressing Magic+d. See Magic Commands.
  • set debug_enable=true usually in matrix_init() in matrix.c.
  • try using 'print' function instead of debug print. See common/print.h.
  • disconnect other devices with console function. See Issue #97.

Linux or UNIX like system requires Super User privilege

Just use 'sudo' to execute hid_listen with privilege.

$ sudo hid_listen

Or add an udev rule for TMK devices with placing a file in rules directory. The directory may vary on each system.

File: /etc/udev/rules.d/52-tmk-keyboard.rules(in case of Ubuntu)

# tmk keyboard products
SUBSYSTEMS=="usb", ATTRS{idVendor}=="feed", MODE:="0666"


NKRO Doesn't work

First you have to compile frimware with this build option NKRO_ENABLE in Makefile.

Try Magic N command(LShift+RShift+N by default) when NKRO still doesn't work. You can use this command to toggle between NKRO and 6KRO mode temporarily. In some situations NKRO doesn't work you need to switch to 6KRO mode, in particular when you are in BIOS.

If your firmeare built with BOOTMAGIC_ENABLE you need to turn its switch on by BootMagic N command(Space+N by default). This setting is stored in EEPROM and keeped over power cycles.

TrackPoint needs reset circuit(PS/2 mouse support)

Without reset circuit you will have inconsistent reuslt due to improper initialize of the hardware. See circuit schematic of TPM754.

Can't read column of matrix beyond 16

Use 1UL<<16 instead of 1<<16 in read_cols() in [matrix.h] when your columns goes beyond 16.

In C 1 means one of [int] type which is [16bit] in case of AVR so you can't shift left more than 15. You will get unexpected zero when you say 1<<16. You have to use [unsigned long] type with 1UL.

Bootloader jump doesn't work

Properly configure bootloader size in Makefile. With wrong section size bootloader won't probably start with Magic command and Boot Magic.

# Size of Bootloaders in bytes:
#   Atmel DFU loader(ATmega32U4)   4096    
#   Atmel DFU loader(AT90USB128)   8192    
#   LUFA bootloader(ATmega32U4)    4096             
#   Arduino Caterina(ATmega32U4)   4096             
#   USBaspLoader(ATmega***)        2048             
#   Teensy   halfKay(ATmega32U4)   512              
#   Teensy++ halfKay(AT90USB128)   2048

AVR Boot section size are defined by setting BOOTSZ fuse in fact. Consult with your MCU datasheet. Note that Word(2 bytes) size and address are used in datasheet while TMK uses Byte.

AVR Boot section is located at end of Flash memory like the followings.

byte     Atmel/LUFA(ATMega32u4)          byte     Atmel(AT90SUB1286)
0x0000   +---------------+               0x00000  +---------------+
         |               |                        |               |
         |               |                        |               |
         |  Application  |                        |  Application  |
         |               |                        |               | 
         =               =                        =               =
         |               | 32KB-4KB               |               | 128KB-8KB
0x6000   +---------------+               0x1E000  +---------------+
         |  Bootloader   | 4KB                    |  Bootloader   | 8KB
0x7FFF   +---------------+               0x1FFFF  +---------------+

byte     Teensy(ATMega32u4)              byte     Teensy++(AT90SUB1286)
0x0000   +---------------+               0x00000  +---------------+
         |               |                        |               |
         |               |                        |               |
         |  Application  |                        |  Application  |
         |               |                        |               |
         =               =                        =               =
         |               | 32KB-512B              |               | 128KB-2KB
0x7E00   +---------------+               0x1FC00  +---------------+
         |  Bootloader   | 512B                   |  Bootloader   | 2KB
0x7FFF   +---------------+               0x1FFFF  +---------------+

And see this discussion for further reference.

Special Extra key doesn't work(System, Audio control keys)

You need to define EXTRAKEY_ENABLE in to use them in QMK.

EXTRAKEY_ENABLE = yes          # Audio control and System control

Wakeup from sleep doesn't work

In Windows check Allow this device to wake the computer setting in Power Management property tab of Device Manager. Also check BIOS setting.

Pressing any key during sleep should wake host.

Using Arduino?

Note that Arduino pin naming is different from actual chip. For example, Arduino pin D0 is not PD0. Check circuit with its schematics yourself.

Arduino leonardo and micro have ATMega32U4 and can be used for TMK, though Arduino bootloader may be a problem.

Using PF4-7 pins of USB AVR?

You need to set JTD bit of MCUCR yourself to use PF4-7 as GPIO. Those pins are configured to serve JTAG function by default. MCUs like ATMegaU or AT90USB* are affeteced with this.

If you are using Teensy this isn't needed. Teensy is shipped with JTAGEN fuse bit unprogrammed to disable the function.

See this code.

    // JTAG disable for PORT F. write JTD bit twice within four cycles.
    MCUCR |= (1<<JTD);
    MCUCR |= (1<<JTD);

And read 26.5.1 MCU Control Register – MCUCR of ATMega32U4 datasheet.

Adding LED indicators of Lock keys

You need your own LED indicators for CapsLock, ScrollLock and NumLock? See this post.

Program Arduino Micro/Leonardo

Push reset button and then run command like this within 8 seconds.

avrdude -patmega32u4 -cavr109 -b57600 -Uflash:w:adb_usb.hex -P/dev/ttyACM0

Device name will vary depending on your system.

USB 3 compatibility

I heard some people have a problem with USB 3 port, try USB 2 port.

Mac compatibility

OS X 10.11 and Hub

Problem on BIOS(UEFI)/Resume(Sleep&Wake)/Power cycles

Some people reported their keyboard stops working on BIOS and/or after resume(power cycles).

As of now root of its cause is not clear but some build options seem to be related. In Makefile try to disable those options like CONSOLE_ENABLE, NKRO_ENABLE, SLEEP_LED_ENABLE and/or others.

FLIP doesn't work

AtLibUsbDfu.dll not found

Remove current driver and reinstall one FLIP provides from DeviceManager.

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