[QMK](https://github.com/qmk), short for Quantum Mechanical Keyboard, is a group of people building tools for custom keyboards. We started with the [QMK firmware](https://github.com/qmk/qmk_firmware), a heavily modified fork of [TMK](https://github.com/tmk/tmk_keyboard).
TMK was originally designed and implemented by [Jun Wako](https://github.com/tmk). QMK started as [Jack Humbert's](https://github.com/jackhumbert) 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](quantum_keycodes.html).
From a project and community management standpoint TMK prefers to have keyboards maintained in separate forks while QMK prefers to have keyboards maintained in one central repository.
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.
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`.
**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 ATMega*U* 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.
## 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.
