Now that you've built a custom firmware file you'll want to flash your keyboard.
## Put Your Keyboard into DFU (Bootloader) Mode
In order to flash your custom firmware you must first put your keyboard into a special flashing mode. While it is in this mode you will not be able to type or otherwise use your keyboard. It is very important that you do not unplug the keyboard or otherwise interrupt the flashing process while the firmware is being written.
Different keyboards have different ways to enter this special mode. If your PCB currently runs QMK, TMK, or PS2AVRGB (Bootmapper Client) and you have not been given specific instructions, try the following, in order:
* Hold down both shift keys and press `Pause`
* Hold down both shift keys and press `B`
* Unplug your keyboard, hold down the Spacebar and `B` at the same time, plug in your keyboard and wait a second before releasing the keys
* Unplug your keyboard, hold down the top or bottom left key (usually Escape or Left Control) and plug in your keyboard
* Press the physical `RESET` button, usually located on the underside of the PCB
* Locate header pins on the PCB labeled `RESET` and `GND`, and short them together while plugging your PCB in
If you've attempted all of the above to no avail, and the main chip on the board says `STM32` or `RP2-B1` on it, this may be a bit more complicated. Generally your best bet is to ask on [Discord](https://discord.gg/qmk) for assistance. It's likely some photos of the board will be asked for -- if you can get them ready beforehand it'll help move things along!
However, the Toolbox is currently only available for Windows and macOS. If you're using Linux (or just wish to flash the firmware from the command line), skip to the [Flash your Keyboard from the Command Line](#flash-your-keyboard-from-the-command-line) section.
Begin by opening the QMK Toolbox application. You'll want to locate the firmware file in Finder or Explorer. Your keyboard firmware may be in one of two formats- `.hex` or `.bin`. QMK tries to copy the appropriate one for your keyboard into the root `qmk_firmware` directory.
Once you have located your firmware file, drag it into the "Local file" box in QMK Toolbox, or click "Open" and navigate to where your firmware file is stored.
This has been made pretty simple compared to what it used to be. When you are ready to compile and flash your firmware, open up your terminal window and run the flash command:
If you did not configure your keyboard/keymap name in the CLI according to the [Configure your build environment](newbs_getting_started) section, or you have multiple keyboards, you can specify the keyboard and keymap:
This will check the keyboard's configuration, and then attempt to flash it based on the specified bootloader. This means that you don't need to know which bootloader that your keyboard uses. Just run the command, and let the command do the heavy lifting.
However, this does rely on the bootloader being set by the keyboard. If this information is not configured, or you're using a board that doesn't have a supported target to flash it, you will see this error:
Congrats! Your custom firmware has been programmed to your keyboard and you're ready to test it out!
With a little bit of luck everything will work perfectly, but if not there are steps that will help you figure out what's wrong.
Testing your keyboard is usually pretty straightforward. Press every single key and make sure it sends the keys you expect. You can use [QMK Configurator](https://config.qmk.fm/#/test/)'s test mode to check your keyboard, even if it doesn't run QMK.
