Tuning your mechanical keyboard firmware


In a previous post, I built an awesome mechanical keyboard. The cool thing is that the board I chose supports qmk. That means that building the keyboard is only half the fun, the other half is tuning the software to fit my needs.

Missing keys

The layout I chose doesn’t have function keys. I find them unnecessary most of the time. But in fact, there are a few shortcuts that need them that I actually use sometime:

  • ALT-F4: to close a window in Gnome
  • F2: to rename a file in Gnome file manager
  • CTRL-ALT-F{1,8}: to switch to a virtual console

I also neither have a SUPPR nor an INSERT key. I never toggle in insert mode and I don’t use much the SUPPR key. So that’s OK. But more annoying, that means that these shortcuts don’t work either:

  • CTRL-ALT-SUPPR: reboot the machine
  • SHIFT-INSERT: paste highlighted text in X terminals

And lastly, I don’t really have room for the APP key: the key used to trigger a context menu in most GUI.

qmk to the rescue

qmk is an open source firmware for keyboards. It support a huge number of boards and has plenty of features. In its repository, it has a lot of examples for the different boards it supports. I recommend starting from there by copying an existing firmware source for your board, then tweak it to fit your needs.

Additional layer

First of all, I made all all missing keys available on an additional layer. This is the same feature one can find on laptop keyboards to access special keys such as multimedia keys, multi screen toggle, or WiFi activation. qmk is able to handle up to 16 layers which should be more than enough for any power user.

This is my base layer. It strictly follows the ISO-AZERTY-FR layout I wanted. I only changed CAPSLOCK to ESC as I am a heavy vim user. I also wanted to have an easy access to HOME, END, PAGEUP and PAGEDOWN, so I made these keys available on the right row.

/* Keymap _BL: (Base Layer) Default Layer
 * ,----------------------------------------------------------------.
 * |²  |  &|  é|  "|  '|  (|  -|  è|  _|  ç|  à|  )|  =|Backsp |Home|
 * |----------------------------------------------------------------|
 * |Tab  |  A|  Z|  E|  R|  T|  Y|  U|  I|  O|  P|  ^|  $|     |PgUp|
 * |-------------------------------------------------------    -----|
 * |ESC    |  Q|  S|  D|  F|  G|  H|  J|  K|  L|  M| ù|  *|Entr|PgDn|
 * |----------------------------------------------------------------|
 * |Shift|   <|  W|  X|  C|  V|  B|  N|  ,|  ;|  :| !|Rshift|Up|End |
 * |----------------------------------------------------------------|
 * |Ctrl |Win/App|Alt|         Space       |Agr|Ctrl|Fn|Lef|Dow|Rig |
 * `----------------------------------------------------------------'

And this is my additional layer, temporarily available when holding the FUNCTION key.

/* Keymap _FL1: Function Layer 1
 * ,----------------------------------------------------------------.
 * |ESC| F1| F2| F3| F4| F5| F6| F7| F8| F9|F10|F11|F12| Delete| Ins|
 * |----------------------------------------------------------------|
 * |RESET|   | ↑ |   |   |   |   |   |   |   |   |   |   |     | NXT|
 * |-------------------------------------------------------    -----|
 * |       | ← | ↓ | → |   |   |   |   |   |   |   |  |   |    | PRV|
 * |----------------------------------------------------------------|
 * |HUI |SAI|VAI |RGBMOD| L+|LED| L-|   |   |    |   |  |Play|V+|Mut|
 * |----------------------------------------------------------------|
 * |HUD |SAD |VAD |         RGB_Tog       |   |   |   | << | V-| >> |
 * `----------------------------------------------------------------'

I put the missing keys as close as possible to their original position. Along the missing keys, I also added a few handy multimedia keys.

Combo events

Having these keys available on a separate layer makes the shortcuts that use them even more complicated than they are. For example CTRL-ALT-SUPPR is already a three keys shortcut, can I avoid to make it a four keys shortcut ?

The combo events feature of qmk allows to map a shortcut to a new one. That means that I can make my keyboard send CTRL-ALT-SUPPR when I hit CTRL-ALT-DEL which is pretty close to the original shortcut.

Below is the full list of shortcuts I have remapped with qmk:

From To

App key

One last thing is that missing APP key. It is not that I use it very often but I thought I needed to make it available for completeness. I could have put it on the additional layer on top of the WIN key. But there is already a light control keys their.

So I used another neat qmk feature which is tap dance. When I hit the WIN key twice during a short interval of time, the keyboard sends the APP key to the computer.

Upgrade procedure

This firmware is available on my github like most of my projects. I put here for the record how to setup, compile and flash the firmware to the keyboard.

First, one needs to access the keyboard as an unprivileged user, this udev rule to be put in configuration.nix adds the needed rights to the users group.

# Additional udev rule for qmk
services.udev.extraRules = "SUBSYSTEMS==\"usb\", ATTRS{idVendor}==\"03eb\", ATTRS{idProduct}==\"2ff4\", GROUP+=\"users\"";

Then the initial setup, it writes the default keyboard and keymap in the file ~/.config/qmk/qmk.ini.

$ nix-shell
$ qmk config user.keyboard=xd68
$ qmk config user.keymap=jecaro_iso_azerty

To compile the firmware:

$ qmk compile

To install, one need to put the keyboard in a special mode called DFU mode by pressing RESET with FUNCTION-TAB.

$ qmk flash

And that’s it !


qmk is pretty awesome. Its documentation is great. It requires a bit of reading to find out how the different features work and what is the best for one needs. But after that everything is pretty smoothly. And it feels good to be able to tune just everything about the keyboard that I use everyday.

October 6, 2021