[Docs] Update ISP Flashing guide (#8149)

* [Docs] Update ISP Flashing guide

* Apply suggestions from code review

AKA why you shouldn't write docs at 2am

Co-Authored-By: fauxpark <fauxpark@gmail.com>
Co-Authored-By: James Young <18669334+noroadsleft@users.noreply.github.com>

* Update workding for planck-qmk-dfu

Co-authored-by: Ryan <fauxpark@gmail.com>
Co-authored-by: James Young <18669334+noroadsleft@users.noreply.github.com>

docs/isp_flashing_guide.md

@@ -1,6 +1,14 @@
 # ISP Flashing Guide
 
-If you're having trouble flashing/erasing your board, and running into cryptic error messages like any of the following:
+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:
 
     libusb: warning [darwin_transfer_status] transfer error: timed out
     dfu.c:844: -ETIMEDOUT: Transfer timed out, NAK 0xffffffc4 (-60)
@@ -19,16 +27,60 @@ If you're having trouble flashing/erasing your board, and running into cryptic e
     Memory write error, use debug for more info.
     commands.c:360: Error writing memory data. (err -4)
 
-You're likely going to need to ISP flash your board/device to get it working again. Luckily, this process is pretty straight-forward, provided you have any extra programmable keyboard, Pro Micro, or Teensy 2.0/Teensy 2.0++. There are also dedicated ISP flashers available for this, but most cost >$15, and it's assumed that if you are googling this error, this is the first you've heard about ISP flashing, and don't have one readily available (whereas you might have some other AVR board). __We'll be using a Teensy 2.0 or Pro Micro with Windows 10 in this guide__ - if you are comfortable doing this on another system, please consider editing this guide and contributing those instructions!   
+Or, if you see this sort of message for a Pro Micro based controller:
+
+    avrdude: butterfly_recv(): programmer is not responding
+    avrdude: butterfly_recv(): programmer is not responding
+    avrdude: verification error, first mismatch at byte 0x002a
+            0x2b != 0x75
+    avrdude: verification error; content mismatch
+    avrdude: verification error; content mismatch
+
+
+You're likely going to need to ISP flash your board/device to get it working again. 
+
+## Hardware Needed
+
+You'll need one of the following to actually perform the ISP flashing (followed by the protocol they use):
+
+* [SparkFun PocketAVR](https://www.sparkfun.com/products/9825) - (USB Tiny)
+* [USBtinyISP AVR Programmer Kit](https://www.adafruit.com/product/46) - (USB Tiny)
+* [Teensy 2.0](https://www.pjrc.com/store/teensy.html) - (avrisp)
+* [Pro Micro](https://www.sparkfun.com/products/12640)  - (avrisp)
+* [Bus Pirate](https://www.adafruit.com/product/237) - (buspirate)
+
+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. 
+
+* Teensy 2.0: [`util/teensy_2.0_ISP_B0.hex`](https://github.com/qmk/qmk_firmware/blob/master/util/teensy_2.0_ISP_B0.hex) (`B0`)
+* Pro Micro: [`util/pro_micro_ISP_B6_10.hex`](https://github.com/qmk/qmk_firmware/blob/master/util/pro_micro_ISP_B6_10.hex) (`10/B6`)
+
+Once you've flashed your controller, you won't need this hex file anymore. 
 
 ## Software Needed
 
-* [Teensy Loader](https://www.pjrc.com/teensy/loader.html) (if using a Teensy)
+The QMK Toolbox can be used for most (all) of this.  
-* QMK Toolbox (flash as usual - be sure to select the correct MCU) or `avrdude` via [WinAVR](http://www.ladyada.net/learn/avr/setup-win.html) (for Teensy & Pro Micro)
+
+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. 
+
 
 ## Wiring
 
-This is pretty straight-forward - we'll be connecting like-things to like-things in the following manner:
+This is pretty straight-forward - we'll be connecting like-things to like-things in the following manner.
+
+### SparkFun Pocket AVR
+
+    PocketAVR RST  <-> Keyboard RESET
+    PocketAVR SCLK <-> Keyboard B1 (SCLK)
+    PocketAVR MOSI <-> Keyboard B2 (MOSI)
+    PocketAVR MISO <-> Keyboard B3 (MISO)
+    PocketAVR VCC  <-> Keyboard VCC
+    PocketAVR GND  <-> Keyboard GND
 
 ### Teensy 2.0
 
@@ -39,6 +91,8 @@ This is pretty straight-forward - we'll be connecting like-things to like-things
     Teensy VCC <-> Keyboard VCC
     Teensy GND <-> Keyboard GND
     
+!> 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. 
+
 ### Pro Micro
 
     Pro Micro 10 (B6)  <-> Keyboard RESET
@@ -48,45 +102,61 @@ This is pretty straight-forward - we'll be connecting like-things to like-things
     Pro Micro VCC      <-> Keyboard VCC
     Pro Micro GND      <-> Keyboard GND
 
-## The ISP Firmware (now pre-compiled)
+!> 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 only difference between the .hex files below is which pin is connected to RESET. You can use them on other boards as well, as long as you're aware of the pins being used. If for some reason neither of these pins are available, [create an issue](https://github.com/qmk/qmk_firmware/issues/new), and we can generate one for you!
 
-* Teensy 2.0: [`util/teensy_2.0_ISP_B0.hex`](https://github.com/qmk/qmk_firmware/blob/master/util/teensy_2.0_ISP_B0.hex) (`B0`)
+## Flashing Your Keyboard 
-* Pro Micro: [`util/pro_micro_ISP_B6_10.hex`](https://github.com/qmk/qmk_firmware/blob/master/util/pro_micro_ISP_B6_10.hex) (`B6/10`)
 
-**Flash your Teenys/Pro Micro with one of these and continue - you won't need the file after flashing your ISP device.**
+After you have your ISP programmer set up, and wired to your keyboard, it's time to flash your keyboard.  
 
-## Just the Bootloader File
+### The Bootloader File
 
-If you just want to get things back to normal, you can flash only a bootloader from [`util/` folder](https://github.com/qmk/qmk_firmware/tree/master/util), and use your normal process to flash the firmware afterwards. Be sure to flash the correct bootloader for your chip:
+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:
 
 * [`atmega32u4`](https://github.com/qmk/qmk_firmware/blob/master/util/bootloader_atmega32u4_1_0_0.hex) - Most keyboards, Planck Rev 1-5, Preonic Rev 1-2
+* [`Pro Micro`](https://github.com/sparkfun/Arduino_Boards/blob/master/sparkfun/avr/bootloaders/caterina/Caterina-promicro16.hex) - The default bootloader for Pro Micro controllers
 * [`at90usb1286`](https://github.com/qmk/qmk_firmware/blob/master/util/bootloader_at90usb128x_1_0_1.hex) - Planck Light Rev 1
-* [`atmega32a`](https://github.com/qmk/qmk_firmware/blob/master/util/bootloader_atmega32a_1_0_0.hex) - jj40
+* [`atmega32a`](https://github.com/qmk/qmk_firmware/blob/master/util/bootloader_atmega32a_1_0_0.hex) - jj40, and other V-USB/ps2avrGB keyboards
 
 If you're not sure what your board uses, look in the `rules.mk` file for the keyboard in QMK. The `MCU =` line will have the value you need. It may differ between different versions of the board.
 
-### Advanced/Production Techniques
+### Production Techniques
 
-If you'd like to flash both the bootloader **and** the regular firmware at the same time, you need to combine the files. 
+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. 
+
+To do this manually: 
 
 1. Open the original firmware .hex file in a text editor
 2. Remove the last line (which should be `:00000001FF` - this is an EOF message)
 3. Copy the entire bootloader's contents onto a new line (with no empty lines between) and paste it at the end of the original file
 4. Save it as a new file by naming it `<keyboard>_<keymap>_production.hex`
 
-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.
+?> 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.
 
 ## Flashing Your Bootloader/Production File
 
-Make sure your keyboard is unplugged from any device, and plug in your Teensy.
+Make sure your keyboard is unplugged from any device, and plug in your ISP Programmer.
+
+If you want to change bootloader types, You'll need to use the command line. 
 
 ### QMK Toolbox
 
-1. `AVRISP device connected` will show up in yellow
+1. `AVRISP device connected` or `USB Tiny device connected` will show up in yellow
 2. Select the correct bootloader/production .hex file with the `Open` dialog (spaces can't be in the path)
-3. Be sure the correct `Microcontroller` option is selected
+3. Be sure the correct `Microcontroller` option for the keyboard you're flashing (not the ISP programmer) is selected
 4. Hit `Flash`
 5. Wait, as nothing will output for a while, especially with production files
 
@@ -94,7 +164,7 @@ If the verification and fuse checks are ok, you're done! Your board may restart
 
 ### Command Line
 
-Open `cmd` 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:
+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:
 
     avrdude -c avrisp -P COM3 -p atmega32u4
 
@@ -129,4 +199,47 @@ You should see a couple of progress bars, then you should see:
 
 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: 
+
+    avrdude -c avrisp -P COM3 -p atmega32u4 -U flash:w:main.hex:i -U lfuse:w:0x5E:m -U hfuse:w:0xD9:m -U efuse:w:0xC3:m
+
+For Caterina on the `atmega32u4`, these are the fuse settings that you want: 
+
+| Fuse     | Setting|
+|----------|--------|
+| Low      | `0xFF` |
+| High     | `0xD9` |
+| Extended | `0xC3` |
+
+To set this add `-U lfuse:w:0xFF:m -U hfuse:w:0xD8:m -U efuse:w:0xC3:m` to your command.  So the final command should look something like: 
+
+    avrdude -c avrisp -P COM3 -p atmega32u4 -U flash:w:main.hex:i -U lfuse:w:0xFF:m -U hfuse:w:0xD8:m -U efuse:w:0xC3:m
+
+
+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.
+
+## Help 
+
 If you have any questions/problems, feel free to [open an issue](https://github.com/qmk/qmk_firmware/issues/new)!