ISP flashing (also known as ICSP flashing) is the process of programming a microcontroller directly. This allows you to replace the bootloader, or change the "fuses" on the controller, which control a number of hardware- and software-related functions, such as the speed of the controller, how it boots, and other options.
The main use of ISP flashing for QMK is flashing or replacing the bootloader on your AVR-based controller (Pro Micros, or V-USB chips).
?> This is only for programming AVR based boards, such as the Pro Micro or other ATmega controllers. It is not for Arm controllers, such as the Proton C.
## Dealing with Corrupted Bootloaders
If you're having trouble flashing/erasing your board, and running into cryptic error messages like any of the following for a DFU based controller:
There are other devices that can be used to ISP flash, but these are the main ones. Also, all product links are to the official versions. You can source them elsewhere.
You'll also need something to wire your "ISP Programmer" to the device that you're programming. Some PCBs may have ISP headers that you can use directly, but this often isn't the case, so you'll likely need to solder to the controller itself or to different switches or other components.
### The ISP Firmware
The Teensy and Pro Micro controllers will need you to flash the ISP firmware to the controllers before you can use them as an ISP programmer. The rest of the hardware should come preprogrammed. So, for these controllers, download the correct hex file, and flash it first.
The QMK Toolbox can be used for most (all) of this.
However, you can grab the [Teensy Loader](https://www.pjrc.com/teensy/loader.html) to flash your Teensy 2.0 board, if you are using that. Or you can use `avrdude` (installed as part of `qmk_install.sh`), or [AVRDUDESS](https://blog.zakkemble.net/avrdudess-a-gui-for-avrdude/) (for Windows) to flash the Pro Micro, and the ISP flashing.
!> Note that the B0 pin on the Teensy is wired to the RESET/RST pin on the keyboard's controller. ***DO NOT*** wire the RESET pin on the Teensy to the RESET on the keyboard.
!> Note that the 10/B6 pin on the Pro Micro is wired to the RESET/RST pin on the keyboard's controller. ***DO NOT*** wire the RESET pin on the Pro Micro to the RESET on the keyboard.
The simplest and quickest way to get things back to normal is to flash only a bootloader to the keyboard. Once this is done, you can connect the keyboard normally and flash the keyboard like you normally would.
You can find the stock bootloaders in the [`util/` folder](https://github.com/qmk/qmk_firmware/tree/master/util). Be sure to flash the correct bootloader for your chip:
If you're not sure what your board uses, look in the `rules.mk` file for the keyboard in QMK. The `MCU` and `BOOTLOADER` lines will have the value you need. It may differ between different versions of the board.
If you'd like to flash both the bootloader **and** the regular firmware at the same time, there are two options to do so. Manually, or with the `:production` target when compiling.
?> It's possible to use other bootloaders here in the same way, but __you need a bootloader__, otherwise you'll have to use ISP again to write new firmware to your keyboard.
To do this the easy way, you can flash the board using the `:production` target when compiling. This compiles the firmware, then compiles the QMK DFU bootloader, and then creates a combined image. Once this is done, you'll see three files:
*`<keyboard>_<keymap>.hex`
*`<keyboard>_<keymap>_bootloader.hex`
*`<keyboard>_<keymap>_production.hex`
The QMK DFU bootloader has only really been tested on `atmega32u4` controllers (such as the AVR based Planck boards, and the Pro Micro), and hasn't been tested on other controllers. However, it will definitely not work on V-USB controllers, such as the `atmega32a` or `atmega328p`.
You can flash either the bootloader or the production firmware file. The production firmware file will take a lot longer to flash, since it's flashing a lot more data.
?> Note: You should stay with the same bootloader. If you're using DFU already, switching to QMK DFU is fine. But flashing QMK DFU onto a Pro Micro, for instance, has additional steps needed.
5. Wait, as nothing will output for a while, especially with production files
If the verification and fuse checks are ok, you're done! Your board may restart automatically, otherwise, unplug your Teensy and plug in your keyboard - you can leave your Teensy wired to your keyboard while testing things, but it's recommended that you desolder it/remove the wiring once you're sure everything works.
Open a terminal (`cmd` on Windows, for instance) and navigate to your where your modified .hex file is. We'll pretend this file is called `main.hex`, and that your Teensy 2.0 is on the `COM3` port - if you're unsure, you can open your Device Manager, and look for `Ports > USB Serial Device`. Use that COM port here. You can confirm it's the right port with:
Which means everything should be ok! Your board may restart automatically, otherwise, unplug your Teensy and plug in your keyboard - you can leave your Teensy wired to your keyboard while testing things, but it's recommended that you desolder it/remove the wiring once you're sure everything works.
If you're using a SparkFun PocketAVR Programmer, or another USB Tiny based ISP programmer, you will want to use something like this:
avrdude -c usbtiny -P usb -p atmega32u4
#### Advanced: Changing Fuses
If you're switching bootloaders, such as flashing QMK DFU on a Pro Micro, you will need to change the fuses, in additional to flashing the bootloader hex file. This is because `caterina` (the Pro Micro bootloader) and `dfu` handle the startup routines differently, and that behavior is controlled by the fuses.
!> This is one area that it is very important to be careful, as changing fuses is one of the ways that you can permanently brick your controller.
For this, we are assuming the 5V 16MHz versions of the `atmega32u4` (such as the 5V Pro Micro).
For DFU on the `atmega32u4`, these are the fuse settings that you want:
| Fuse | Setting |
|----------|------------------|
| Low | `0x5E` |
| High | `0xD9` or `0x99` |
| Extended | `0xC3` |
The High fuse can be 0xD9 or 0x99. The difference is that 0xD9 disables JTAG, which QMK Firmware disables via software as well, while 0x99 doesn't disable JTAG.
To set this add `-U lfuse:w:0x5E:m -U hfuse:w:0xD9:m -U efuse:w:0xC3:m` to your command. So the final command should look something like:
If you are using a different controller or want different configuration, you can use [this AVR Fuse Calculator](http://www.engbedded.com/fusecalc/) to find a better value for you.
