zmk-config

This is my personal ZMK firmware configuration. It is ported from my QMK configuration, which in turn is heavily inspired by Manna Harbour's Miryoku layout.

Key features

• clean keymap config + unicode support using zmk-nodefree-config
• home-row mods on base layer (with the perfect configuration, sticky mods on Nav and Num layers
• most symbols can be accessed from the base layer via combos
• sticky shift on right thumb, double-tap activates caps-word
• backspace morphs into delete when shifted
• full numpad-layer with arithmetic operators (= via combo) and Esc, Enter, Tab on left hand (can be numlocked via W + P combo, ideal for data entry and right-handed mouse)
• "Greek" layer for mathematical typesetting

Timeless homerow mods

Homerow mods are great. But they can require some finicky timings: In the most naive version, in order to produce a "mod" they must be held longer than tapping-term-ms. While in order to produce a "tap", they must be held less than tapping-term-ms. This requires very consistent typing speeds that, alas, I do not possess. Hence my quest for a "timeless" HRM configuration. Here's what I have ended up with.

Let's suppose for a moment we set tapping-term-ms to something ridiculously large, say 5 seconds. This makes the configuration "timeless". But obviously it creates two undesired side-effects: (1) In order to get a "mod" we now have to hold the HRM keys for something that feels eternity. (2) In normal typing, when tapping keys, there can be long delays between the press of a key and the time it appears on the screen. Enter my two favorite configuration options:

• To alleviate the first side-effect, I use ZMK's balanced flavor, which will produce a "hold" if another key is both pressed and released within the tapping-term. Because that is exactly what I normally do with HRMs, there is virtually never a need to wait past my long tapping term (see below for two exceptions).
• To alleviate the typing delay, I use the global-quick-tap property, which will immediately resolve HRMs as "tap" when they are pressed shortly after another key has been tapped. This all but completely eliminates the delay when typing.

This almost perfect, but there's still a few rough edges:

• While rolling keys quickly, I sometimes unintentionally end up with "nested" key sequences: key 1 down, key 2 down and up, key 1 up. Given the balanced flavor, this would falsely register key 1 as a mod. To prevent this, I use ZMK's "positional hold-tap" feature to force HRMs to always resolved as "tap" when the next key is on the same side of the keyboard. Problem solved.
• In the official ZMK version for positional hold-taps, the check whether the next key is on the same side of the keyboard is done upon key press. This is not ideal, because it prevents combining two modifiers on the same hand. To fix this, I use a small patch that delays the positional-hold-tap decision until key release. This way, multiple mods can be combined, while I still get the benefits of positional-hold-taps when tapping keys. There is no PR yet (I am still in an early testing stage), but if you want to try, this is the testing branch.
• So far, nothing of the configuration depends on the duration of tapping-term-ms. In practice, there are two reasons why I don't set it to eternity:
  1. Sometimes, in rare circumstances, I want to combine a mod with a shortcut-key on the same hand (e.g., when the other hand uses a mouse). Our positional hold-tap configuration prevents this within the tapping term. By setting the tapping term to something large but not crazy large (I use 280ms), I can use same-hand mod + shortcut by by holding the mod just for a a while before pressing the shortcut-key.
  2. Sometimes, I want to press a modifier without another key (e.g., on Windows, tapping the Win key opens the search menu). Since the balanced flavour only kicks in when another key is pressed, this again requires waiting past tapping-term-ms.

Here's my configuration (I use a bunch of helper macros to simplify the syntax, but they are not necessary):

/* use helper macros to define left and right hand keys */
#include "../zmk-nodefree-config/keypos_def/keypos_36keys.h"                // keyposition helpers
#define KEYS_L LT0 LT1 LT2 LT3 LT4 LM0 LM1 LM2 LM3 LM4 LB0 LB1 LB2 LB3 LB4  // left-hand keys
#define KEYS_R RT0 RT1 RT2 RT3 RT4 RM0 RM1 RM2 RM3 RM4 RB0 RB1 RB2 RB3 RB4  // right-hand keys
#define THUMBS LH2 LH1 LH0 RH0 RH1 RH2                                      // thumb keys

/* left-hand HRMs */
ZMK_BEHAVIOR(hml, hold_tap,
    flavor = "balanced";
    tapping-term-ms = <280>;
    quick-tap-ms = <175>;                // double tapping same key allows for repeating
    global-quick-tap-ms = <150>;         // without PR #1387 use global-quick-tap instead
    bindings = <&kp>, <&kp>;
    hold-trigger-key-positions = <KEYS_R THUMBS>;
)

/* right-hand HRMs */
ZMK_BEHAVIOR(hmr, hold_tap,
    flavor = "balanced";
    tapping-term-ms = <280>;
    quick-tap-ms = <175>;                // double tapping same key allows for repeating
    global-quick-tap-ms = <150>;         // without PR #1387 use global-quick-tap instead
    bindings = <&kp>, <&kp>;
    hold-trigger-key-positions = <KEYS_LT THUMBS>;  // include right-hand HRMs for chording
)

One last note, the configuration above uses some syntactic sugar introduced in PR #1387, which decouples the quick-tap-ms timeout from the global-quick-tap-ms timeout. Without the PR, one can replace global-quick-tap-ms = <280> with global-quick-tap for a similar effect (global-quick-tap will use the regular quick-tap-ms timeout in this case).

My personal ZMK fork includes both the global-quick-tap-ms PR as well as the positonal-hold-tap tweak (along with a few other PRs).

A few thoughts on the combo setup

The combo layout is guided by two goals: (1) put all combos in easy-to-access locations, and (2) make them easy to remember. Specifically:

• the top vertical-combo row is almost equivalent to the symbols on standard number rows, making them easy to remember
• the bottom vertical-combo row is set up symmetrically to facilitate memorization (subscript _ aligns with superscript ^; minus - aligns with +; division / aligns with multiplication *; logical-or | aligns with logical-and &; backslash \ aligns horizontally with forward slash /)
• parenthesis, braces and brackets in symmetric positions
• ! and ? are on home-row position for prime access
• a numlock shortcut (on W + P) for one-handed data entry
• shortcuts for cut (on X + D), copy, and paste on the left-hand side for right-handed mouse usage