See [build environment setup](https://docs.qmk.fm/#/getting_started_build_tools) then the [make instructions](https://docs.qmk.fm/#/getting_started_make_guide) for more information.
If you prefer (or are having issues with a `program` flash), you can just build it (`make jj40:<keymap-name>` and flash the firmware (`.hex` file) directly with
Windows sometimes doesn't recognize the jj40. The easiest way of flashing a new layout is probably using [HIDBootFlash](http://vusb.wikidot.com/project:hidbootflash).
1. Go to Windows Device Manager and find the keyboard (plug it in while holding down `Backspace` (`Top Right Key`)). It can be found under Human Interface Devices or under Keyboards.
2. Go to properties and the Details tab to find the hardware ID. You want the VID and the PID (code after the underscore). Plug them into HIDBootFlash and hit Find Device.
3. Use `make jj40:<keymap-name>` to generate the .hex file in the qmk basis folder. Select the .hex file in HIDBootFlash and press Flash Device.
If you flash a bad hex (e.g. you have a V1 board without RGB and compile/flash blindly without editing your rules.mk), your jj40 is now semi-bricked and you're stuck unless you have access to an ISP. The [ISP Flashing Guide](https://docs.qmk.fm/#/isp_flashing_guide) contains very good (but somewhat generalized) information. However, the instructions below should get you up and running provided you have an Arduino or clone.
### Arduino Setup
1. Upload the ArduinoISP sketch onto your Arduino board (https://www.arduino.cc/en/Tutorial/ArduinoISP).
2. Wire the Arduino to the jj40. Match the data pins on the Arduino to those on the jj40. "RST" usually goes to D10 on the Arduino. I didn't need a capacitor when using my Uno.
![Imgur](https://i.imgur.com/oLWJOkQ.jpg)
3. Get a working bootloader from https://blog.winkeyless.kr/m/152. The file is called "main.hex" from the archive called "ps2avrGB_bootloader_161215.zip" Copy "main.hex" to your qmk folder.
Change `comPORT` to whatever port is used by the Arduino (e.g. `com11` in Windows or `/dev/ttyACM0` in Linux). Use Device Manager in Windows to find the port being used. Use `ls /dev/tty*` in Linux.
5. If this process is successful, you should now be able to upload normally.