feat(combos): initial implementation

[okke-formsma]

An implementation of combos for #45

This has been tested by TJ and others for a while, so I think it's pretty good.

example of a keymap using combos:

/ {
	combos {
		compatible = "zmk,combo";
		combo_one {
			timeout-ms = <30>;
			key-positions = <0 1>;
			bindings = <&mt LEFT_CONTROL C>;
		};

		combo_two {
			timeout-ms = <50>;
			key-positions = <0 1 2>;
			bindings = <&kp D>;
		};
	};

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

		default_layer {
			bindings = <
				&kp A &kp B
				&kp Z &kp Y
			>;
		};
	};
};

Docs are still to do.

[okke-formsma]

@joelspadin thanks for your comments! I've addressed each of them.

[okke-formsma]

rebased on 2.4.0

[okke-formsma]

I've identified a minor issue with the combo keys in the ticket: #45 (comment)

I think we should wait merging until this is fixed. Reviews of the code are very welcome in the meantime.

[okke-formsma]

The issue between hold-taps and combos has been fixed, I'll merge in that commit after review.

[okke-formsma]

@petejohanson Can you review soon? I know quite a few people are really looking forward to combos. The branch has been tested by various people (@tominabox1, myself, various others in #testing).

[petejohanson]

/ {
behaviors {
combo_one {
compatible = "zmk,behavior-combo";
label = "COMBO_ONE";
timeout-ms = <30>;
key-positions = <0 1>;
bindings = <&mt LEFT_CONTROL C>;
};

  combo_two {
  	compatible = "zmk,behavior-combo";
  	label = "COMBO_TWO";
  	timeout-ms = <50>;
  	key-positions = <0 1 2>;
  	bindings = <&kp D>;
  };

};

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

  default_layer {
  	bindings = <
  		&kp A &kp B
  		&kp Z &kp Y
  	>;
  };

};
};

@okke-formsma A comment on the DT format: This is a scenario where I I would likely use the DT bindings child-binding approach, and end up with something like:

/ {
	combos {
		compatible = "zmk,behavior-combos";

		combo_one {
			timeout-ms = <30>;
			key-positions = <0 1>;
			bindings = <&mt LEFT_CONTROL C>;
		};

		combo_two {
			timeout-ms = <50>;
			key-positions = <0 1 2>;
			bindings = <&kp D>;
		};
	};

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

		default_layer {
			bindings = <
				&kp A &kp B
				&kp Z &kp Y
			>;
		};
	};
};

It avoids duplication, and leaves the DT more focused. Will review the code soon, but this stuck out as a user experience issue.

[petejohanson]

A few cursory thoughts. Thanks!

[petejohanson]

Instead, can we fill the rest with MAX to avoid extra storage per combo?

[okke-formsma]

This prevents looping over the items to count in other places, so I think it's worth it.

[petejohanson]

Let's do this! Plenty of end user testing on this, code is reasonable architecture and self contained, and can easily be put behind one Kconfig flag later as needed.