Gherkin Wanleg Layout

This is the layout I came up with to preserve a standard QWERTY 104 key ANSI layout as much as possible, in as few layers as possible for a 30 key board. I originally set up a few Tap Dance keys, but dropped half of them in favor of chorded versions since in actual use, they tended to impede typing speed more than their current two-key versions. I've left them in my keymap.c ready for use if anyone wants to try them out:

Legend Name	Single Tap	Double Tap	Hold
null	space	enter	shift
null	backspace	delete	control
Sft//Cp	shift	caps lock	null
Q//Esc	KC_Q	escape	null

Gherkin Flashing

Windows

The standard Gherkin uses a ProMicro (or clone) microcontroller, which has the Caterina bootloader by default.
If you have never flashed your ProMicro with QMK before, you will need to short the RST pin to GND to put it into bootloader mode (you only have 7 seconds to flash once it enters bootloader mode). You may need to touch the RST pin to GND TWICE in quick succession if it doesn't flash with just one touch.
Once connected to your computer, you should be able to flash using
make gherkin:wanleg:avrdude
Once you've been able to successfully flash the ProMicro, you should be able to use the RESET key for future flashes instead of shorting the RST pin.

Linux

First Flash with QMK

The built-in :avrdude QMK target in Linux doesn't work with the default Caterina bootloader on the ProMicro, so we have to use avrdude separately. The instructions below are adapted from https://deskthority.net/workshop-f7/how-to-use-a-pro-micro-as-a-cheap-controller-converter-like-soarer-s-t8448.html

To flash the device, you need to have AVRdude installed. You can do this via your distro's package manager (or compile from source if needed).
Once avrdude has been installed, open a terminal and run ls /dev/tty*
Next, plug in your device and re-run ls /dev/tty* There should be one more device than was seen previously. Make a note of it. For me, it's /dev/ttyACM0.
Navigate to the directory with your .hex file in it. Touch the RST pin to GND TWICE in quick succession, then run the following within 7 seconds:
sudo avrdude -p m32u4 -P YOUR_SERIAL_PORT -c avr109 -U flash:w:YOUR_FILENAME.hex
Replace YOUR_SERIAL_PORT with your serial port's device name, and YOUR_FILENAME.hex with the appropriate filename. For me, it looks like this:
sudo avrdude -p m32u4 -P /dev/ttyACM0 -c avr109 -U flash:w:gherkin_wanleg.hex
If you miss the 7 second window, the ProMicro will leave bootloader mode and the flash will fail. Hit Control + C to exit the avrdude command, connect RST to GND twice quickly, and try the avrdude command again.

Subsequent Flashes with QMK

Re-flashing is similar to the initial flash procedure. Plug in your keyboard, open a terminal and run ls /dev/tty*
Next, hit the RESET key on your keyboard and re-run the ls /dev/tty* command to find your keyboard's serial port.
Flash your keyboard with the avrdude command you used for the initial flash within 7 seconds after hitting RESET.

ProMicro Bootloader Replacement (Caterina to QMK DFU)

If you have an Arduino (or clone), you can replace the bootloader for a few extra features (e.g. no more 7 second "flash window", simplified Linux flashing, blinking LED when the ProMicro is in bootloader mode, ability to exit bootloader mode without unplugging your keyboard, among others). The instructions below have been adapted from https://www.reddit.com/r/olkb/comments/8sxgzb/replace_pro_micro_bootloader_with_qmk_dfu/)

Arduino Setup

Upload the ArduinoISP sketch onto your Arduino board (https://www.arduino.cc/en/Tutorial/ArduinoISP).
Wire the Arduino to the ProMicro

Arduino	ProMicro
10	RST
11	16
12	14
13	15
GND	GND
5V	VCC

Make the QMK DFU .hex

In config.h add the following. This is already set up in qmk_firmware/keyboards/gherkin/wanleg. You only need to do this on other keymaps.

#define QMK_ESC_OUTPUT B4
#define QMK_ESC_INPUT F7
#define QMK_LED B0

The QMK_ESC_ lines define where the bootloader escape key is. Refer to the MATRIX_ROW_PINS and MATRIX_COL_PINS lines in your keyboard's config.h to choose your preferred key.
You hit the bootloader escape key to exit bootloader mode after you've hit the RESET key to enter bootloader mode (e.g. if you change your mind and don't want to flash just then).
On a Gherkin, B4/F7 corresponds to the top-left corner key.
B0 is an indicator light on one of the ProMicro's onboard LEDs. With QMK DFU, it will flash to indicate the ProMicro is in bootloader mode.
You can add #define QMK_SPEAKER C6 if you have a speaker hooked up to pin C6. The Gherkin PCB already uses pin C6 in its switch layout, so you cannot use a speaker on a standard Gherkin.
4. Also, you should add BOOTLOADER = qmk-dfu to your rules.mk file, so it is flagged properly. Again, this is already set up in qmk_firmware/keyboards/gherkin/wanleg.
5. Once you've made the required edits, it's time to compile the firmware. If you use the :production target when compiling, it will produce the usual .hex file as well as _bootloader.hex and _production.hex files. The _production.hex will be what we want. This contains the bootloader and the firmware, so we only have to flash once (rather than flash the bootloader, and THEN flash the firmware). For example
make <keyboard>:<keymap>:production
For my particular keymap, for reasons listed in the Using QMK DFU section, you should use the following to ensure the bootloader is set properly
make gherkin:wanleg:production dfu=qmk

Burn QMK DFU

Navigate to the directory with your _production.hex file, and burn it with the following command
avrdude -b 19200 -c avrisp -p m32u4 -v -e -U lock:w:0x3F:m -U efuse:w:0xC3:m -U hfuse:w:0xD9:m -U lfuse:w:0x5E:m -U YOUR_production.hex -P comPORT
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. Change YOUR_production.hex to whatever you've created in the previous step.

Using QMK DFU

Once QMK DFU is burned to your ProMicro, you can then flash subsequent hex files with make gherkin:<keymap>:dfu dfu=qmk
The dfu=qmk conditional will set BOOTLOADER = qmk-dfu instead of BOOTLOADER = caterina

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