A ZMK implementation of Nick Conway's tri-state behavior for the ZMK Firmware.

This project demonstrates how to implement custom behaviors without maintaining a separate ZMK fork. It's fully compatible with the latest Zephyr 3.5 release.

Add this module to your ZMK config by modifying your config/west.yml file. Add the necessary remotes and projects sections as shown below:

manifest:
  remotes:
    - name: zmkfirmware
      url-base: https://github.com/zmkfirmware
    - name: dhruvinsh
      url-base: https://github.com/dhruvinsh
  projects:
    - name: zmk
      remote: zmkfirmware
      revision: main
      import: app/west.yml
    - name: zmk-tri-state
      remote: dhruvinsh
      revision: main
  self:
    path: config

For a complete example configuration, see my ZMK config.

NOTE: Common use-cases have not yet been defined for this behavior in the DTSI format. See ZMK documentation for more information.

Add the tri-state behavior to your keymap:

#include <dt-bindings/zmk/keys.h>

/ {
  behaviors {
    swapper: swapper {
      compatible = "zmk,behavior-tri-state";
      #binding-cells = <0>;
      bindings = <&kp A>, <&kp B>, <&kt C>;
    };
  };
};

After defining it, you can use &swapper anywhere in your keymap. See the detailed documentation below for more information and check out a working example here.

Tri-States are a way to have something persist while other behaviors occur.

The tri-state key will fire the 'start' behavior when the key is pressed for the first time. Subsequent presses of the same key will output the second, 'continue' behavior, and any key position or layer state change that is not specified (see below) will trigger the 'interrupt behavior'.

The following is a basic definition of a tri-state:

/ {
    behaviors {
        tri-state: tri-state {
            compatible = "zmk,behavior-tri-state";
            label = "TRI-STATE";
            #binding-cells = <0>;
            bindings = <&kp A>, <&kp B>, <&kt C>;
        };
    };

    keymap {
        compatible = "zmk,keymap";
        label ="Default keymap";

        default_layer {
            bindings = <
                &tri-state  &kp D
                &kp E       &kp F>;
        };
    };
};

Pressing tri-state will fire the first behavior, and output A, as well as the second behavior, outputting B. Subsequent presses of tri-state will output B. When another key is pressed or a layer change occurs, the third, 'interrupt' behavior will fire.

Setting timeout-ms will cause the deactivation behavior to fire when the time has elapsed after releasing the Tri-State or a ignored key.

• Including ignored-key-positions in your tri-state definition will let the key positions specified NOT trigger the interrupt behavior when a tri-state is active.
• Pressing any key NOT listed in ignored-key-positions will cause the interrupt behavior to fire.
• Note that ignored-key-positions is an array of key position indexes. Key positions are numbered according to your keymap, starting with 0. So if the first key in your keymap is Q, this key is in position 0. The next key (probably W) will be in position 1, et cetera.
• See the following example, which is an implementation of the popular Swapper from Callum Oakley:

/ {
    behaviors {
        swap: swapper {
            compatible = "zmk,behavior-tri-state";
            label = "SWAPPER";
            #binding-cells = <0>;
            bindings = <&kt LALT>, <&kp TAB>, <&kt LALT>;
            ignored-key-positions = <1>;
        };
    };

    keymap {
        compatible = "zmk,keymap";
        label ="Default keymap";

        default_layer {
            bindings = <
                &swap    &kp LS(TAB)
                &kp B    &kp C>;
        };
    };
};

• The sequence (swap, swap, LS(TAB)) produces (LA(TAB), LA(TAB), LA(LS(TAB))). The LS(TAB) behavior does not fire the interrupt behavior, because it is included in ignored-key-positions.
• The sequence (swap, swap, B) produces (LA(TAB), LA(TAB), B). The B behavior does fire the interrupt behavior, because it is not included in ignored-key-positions.

• By default, any layer change will trigger the end behavior.
• Including ignored-layers in your tri-state definition will let the specified layers NOT trigger the end behavior when they become active (include the layer the behavior is on to accommodate for layer toggling).
• Activating any layer NOT listed in ignored-layers will cause the interrupt behavior to fire.
• Note that ignored-layers is an array of layer indexes. Layers are numbered according to your keymap, starting with 0. The first layer in your keymap is layer 0. The next layer will be layer 1, et cetera.
• Looking back at the swapper implementation, we can see how ignored-layers can affect things

/ {
    behaviors {
        swap: swapper {
            compatible = "zmk,behavior-tri-state";
            label = "SWAPPER";
            #binding-cells = <0>;
            bindings = <&kt LALT>, <&kp TAB>, <&kt LALT>;
            ignored-key-positions = <1 2 3>;
            ignored-layers = <1>;
        };
    };

    keymap {
        compatible = "zmk,keymap";
        label ="Default keymap";

        default_layer {
            bindings = <
                &swap    &kp LS(TAB)
                &kp B    &tog 1>;
        };

        layer2 {
            bindings = <
                &kp DOWN    &kp B
                &tog 2    &trans>;
        };

        layer3 {
            bindings = <
                &kp LEFT  &kp N2
                &trans    &kp N3>;
        };
    };
};

• The sequence (swap, tog 1, DOWN) produces (LA(TAB), LA(DOWN)). The change to layer 1 does not fire the interrupt behavior, because it is included in ignored-layers, and DOWN is in the same position as the tri-state, also not firing the interrupt behavior.
• The sequence (swap, tog 1, tog 2, LEFT) produces (LA(TAB), LEFT. The change to layer 2 does fire the interrupt behavior, because it is not included in ignored-layers.

• Pete Johanson
• Nick Conway
• Cem Aksoylar
• ZMK and Zephyr Teams

• ZMK-NUM-WORD