Minimizing your keyboard layout is a slippery slope. A few
months ago, I built the
[Ferricy](https://github.com/icyphox/ferricy), a
34-key-split-ortho-ergo keyboard. The Ferricy is a fork of
the [Ferris Sweep MX
Bling](https://github.com/davidphilipbarr/Sweep/tree/main/Sweep%20Bling%20MX).

![The Ferricy, designed by [icyphox](https://icyphox.sh)](https://u.peppe.rs/otz.jpg)


My daily use consists of a bit of prose and a lot of
program, my layout has evolved accordingly.

# Base Layer 

![Colemak with no mods](https://u.peppe.rs/base.png)

The base layer contains alphabets, four symbols and four
whitespace keys:

- Alphas: Stock Colemak, with no modifications whatsoever
- Symbols: `. , / ;`
- Whitespace: tab, space, enter, backspace (from left to
  right)

# Layers

Keyboard input is complex and it is impossible to skirt
around it. You can either use a keyboard with enough keys to
supply all possible inputs (a mechanical burden), or you can
use firmware to supply all possible inputs (a cognitive
burden). Layers are a cognitive burden.

I use 3 layers, heavily inspired by
[Miryoku](https://github.com/manna-harbour/miryoku), but
tuned for programming. Excluding the base Colemak layer:

- `NAV`: activated on holding `space` (left thumb)
- `NUM`: activated on holding `tab` (left thumb)
- `SYM`: activated on holding `enter` (right thumb)

## The `NAV` Layer

As the name suggests, this layer is focused on navigation.
Arrow keys and the likes. 

![`NAV`, on holding `space`](https://u.peppe.rs/nav.png)

Using Vim and Colemak means you lose out on HJKL navigation.
However, on activating the `NAV` layer, the right home-row is
converted into arrow keys. In essence, by holding space, I
can navigate Vim with the home-row, or Firefox, or my PDF
reader. I no longer need to look for software that allows
Vim navigation keys, because it is baked into the firmware!
  
My Vim motions are not limited to HJKL. In fact, my Vim
motions are rarely HJKL. I tend to use `}` (next paragraph)
and `)` (next sentence) more often. As a result, these have
found their way into my `NAV` layer, over the likes of
`PgDown` and `End`. Having brackets at my index and middle
fingers is nice for programming too.
  
## The `SYM` Layer

![`SYM`, on holding `enter`](https://u.peppe.rs/sym.png)

This layer contains all the symbols that you would find by
hitting `Shift` and a key on the number row. Probably
noteworthy to Vim users: the symbols are arranged in the
form of a mirrored numpad for exactly one reason: to move
`$` to the left of `^`. It has always annoyed me that `$`
moves the cursor to the end of the line and `^` moves it to
the beginning, but their position on a typical number row
are reversed, 4 comes before 6.

## The `NUM` layer

![`NUM`, on holding `tab`](https://u.peppe.rs/num.png)

Another deviation from Miryoku, the numpad just feels _right_
on my _right_ hand.

# ZMK Combos

If you have been paying close attention, you might have
noticed that `escape` didn't make it to any layer. `escape`
is too crucial to put on a non-base layer, but at the same
time, not as important to deserve a place on the base layer.
That is where ZMK's combos come in. Combos let you tap any
number of keys, and combine them to form a single key. I
have combos set up for underscore, minus, escape and
caps-word (more on caps-word later):

![Combos are almost piano-like](https://u.peppe.rs/combos.png)

# Home-row Mods

Inherited from Miryoku, I have home-row mods for activating
`Super`, `Alt`, `Shift`, `Ctrl` and `Hyper` (`Ctrl + Shift +
Alt + Super`). The idea is to send `T` on tap and `Ctrl` on
hold. Home-row mods are fairly popular, so I'll not go into
the details.

![Super, Alt, Shift, Ctrl, Hyper; on the left half, and
mirrored on the right half](https://u.peppe.rs/homerow.png)

`Hyper` bridges the gap between firmware and software. You
can never configure key combination that, opens Firefox, for
example, through firmware alone. However, with the `Hyper`
key, and some `sxhkd` magic, you can emulate that. Pressing
`Hyper + F` on a keyboard is just two keys, but the key
codes sent are `Ctrl + Shift + Alt + Super + F`. That key
combination is not intercepted by any application as a
shortcut, except for the following `sxhkd` stanza:

```bash
super + alt + shift + ctrl + f
  xdotool search "Mozilla Firefox" windowactivate
```

Alternatively, you can intercept unused `F` keys: `F13`
through `F24`.

Home-row mods are mirrored on each half because it would be
impossible to hit `Ctrl + T` if not; they lie on the same
key.

# Caps-word

Caps-word is a clever caps-lock, built into ZMK. Typing out
constants such as `PORT` with home-row mods would look like
this:

- hold `e` (shift) on left hand, and tap `p` on right hand
- hold `e` (shift) on left hand, and tap `o` on right hand
- hold `s` (shift) on right hand, and tap `r` on left hand
- hold `s` (shift) on right hand, and tap `t` on left hand

This hold-alternate-hold dance gets tiring quickly. With
caps-word, however:

- toggle `caps_word`
- type out `p`, `o`, `r`, `t`
- hit a _break_ character (space, enter will do)
- continue

Caps-word automatically disables capitalization upon
encountering a breaking character, (which are space, enter
or any modifier, by default) right in the firmware!

# Findings

34-keys has been reasonably comfortable to use, for both
prose and program. My palms do not move across the desk at
all, as I reach for keys. I mostly write Rust and Bash, and
my layout has evolved to accomodate special characters from
their grammars (angled brackets and hyphens, specifically).
If you are on a similar journey, I would suggest focusing on
accuracy and comfort over speed. Speed comes with time.