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 firmware 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.
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`.
If you are using a TeensyUSB, there is a [known bug](https://github.com/qmk/qmk_firmware/issues/164) in which the hardware reset button prevents the RESET key from working. Unplugging the keyboard and plugging it back in should resolve the problem.
## Special Extra key doesn't work(System, Audio control keys)
You need to define `EXTRAKEY_ENABLE` in `rules.mk` 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 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.
