Keyboard Scan Configuration

See Configuration Overview for instructions on how to change these settings.

Common

Kconfig

Definition files:

Config	Type	Description	Default
`CONFIG_ZMK_KSCAN_EVENT_QUEUE_SIZE`	int	Size of the event queue for kscan events	4
`CONFIG_ZMK_KSCAN_INIT_PRIORITY`	int	Keyboard scan device driver initialization priority	40
`CONFIG_ZMK_KSCAN_DEBOUNCE_PRESS_MS`	int	Global debounce time for key press in milliseconds	-1
`CONFIG_ZMK_KSCAN_DEBOUNCE_RELEASE_MS`	int	Global debounce time for key release in milliseconds	-1

If the debounce press/release values are set to any value other than -1, they override the debounce-press-ms and debounce-release-ms devicetree properties for all keyboard scan drivers which support them. See the debouncing documentation for more details.

Devicetree

Applies to: /chosen node

Property	Type	Description
`zmk,kscan`	path	The node for the keyboard scan driver to use
`zmk,matrix_transform`	path	The node for the matrix transform to use

Demux Driver

Keyboard scan driver which works like a regular matrix but uses a demultiplexer to drive the rows or columns. This allows N GPIOs to drive N² rows or columns instead of just N like with a regular matrix.

note

Currently this driver does not honor the CONFIG_ZMK_KSCAN_DEBOUNCE_* settings.

Devicetree

Applies to: compatible = "zmk,kscan-gpio-demux"

Definition file: zmk/app/drivers/zephyr/dts/bindings/kscan/zmk,kscan-gpio-demux.yaml

Property	Type	Description	Default
`label`	string	Unique label for the node
`input-gpios`	GPIO array	Input GPIOs
`output-gpios`	GPIO array	Demultiplexer address GPIOs
`debounce-period`	int	Debounce period in milliseconds	5
`polling-interval-msec`	int	Polling interval in milliseconds	25

Direct GPIO Driver

Keyboard scan driver where each key has a dedicated GPIO.

Kconfig

Definition file: zmk/app/drivers/kscan/Kconfig

Config	Type	Description	Default
`CONFIG_ZMK_KSCAN_DIRECT_POLLING`	bool	Poll for key presses instead of using interrupts	n

Devicetree

Applies to: compatible = "zmk,kscan-gpio-direct"

Definition file: zmk/app/drivers/zephyr/dts/bindings/kscan/zmk,kscan-gpio-direct.yaml

Property	Type	Description	Default
`label`	string	Unique label for the node
`input-gpios`	GPIO array	Input GPIOs (one per key)
`debounce-press-ms`	int	Debounce time for key press in milliseconds. Use 0 for eager debouncing.	5
`debounce-release-ms`	int	Debounce time for key release in milliseconds.	5
`debounce-scan-period-ms`	int	Time between reads in milliseconds when any key is pressed.	1
`diode-direction`	string	The direction of the matrix diodes	`"row2col"`
`poll-period-ms`	int	Time between reads in milliseconds when no key is pressed and `CONFIG_ZMK_KSCAN_DIRECT_POLLING` is enabled.	10
`toggle-mode`	bool	Use toggle switch mode.	n

By default, a switch will drain current through the internal pull up/down resistor whenever it is pressed. This is not ideal for a toggle switch, where the switch may be left in the "pressed" state for a long time. Enabling toggle-mode will make the driver flip between pull up and down as the switch is toggled to optimize for power.

toggle-mode applies to all switches handled by the instance of the driver. To use a toggle switch with other, non-toggle, direct GPIO switches, create two instances of the direct GPIO driver, one with toggle-mode and the other without. Then, use a composite driver to combine them.

Matrix Driver

Keyboard scan driver where keys are arranged on a matrix with one GPIO per row and column.

Definition file: zmk/app/drivers/kscan/Kconfig

Config	Type	Description	Default
`CONFIG_ZMK_KSCAN_MATRIX_POLLING`	bool	Poll for key presses instead of using interrupts	n
`CONFIG_ZMK_KSCAN_MATRIX_WAIT_BEFORE_INPUTS`	int (ticks)	How long to wait before reading input pins after setting output active	0
`CONFIG_ZMK_KSCAN_MATRIX_WAIT_BETWEEN_OUTPUTS`	int (ticks)	How long to wait between each output to allow previous output to "settle"	0

Devicetree

Applies to: compatible = "zmk,kscan-gpio-matrix"

Definition file: zmk/app/drivers/zephyr/dts/bindings/kscan/zmk,kscan-gpio-matrix.yaml

Property	Type	Description	Default
`label`	string	Unique label for the node
`row-gpios`	GPIO array	Matrix row GPIOs in order, starting from the top row
`col-gpios`	GPIO array	Matrix column GPIOs in order, starting from the leftmost row
`debounce-press-ms`	int	Debounce time for key press in milliseconds. Use 0 for eager debouncing.	5
`debounce-release-ms`	int	Debounce time for key release in milliseconds.	5
`debounce-scan-period-ms`	int	Time between reads in milliseconds when any key is pressed.	1
`diode-direction`	string	The direction of the matrix diodes	`"row2col"`
`poll-period-ms`	int	Time between reads in milliseconds when no key is pressed and `CONFIG_ZMK_KSCAN_MATRIX_POLLING` is enabled.	10

The diode-direction property must be one of:

Value	Description
`"row2col"`	Diodes point from rows to columns (cathodes are connected to columns)
`"col2row"`	Diodes point from columns to rows (cathodes are connected to rows)

Composite Driver

Keyboard scan driver which combines multiple other keyboard scan drivers.

Devicetree

Applies to : compatible = "zmk,kscan-composite"

Definition file: zmk/app/dts/bindings/zmk,kscan-composite.yaml

Property	Type	Description
`label`	string	Unique label for the node
`rows`	int	The number of rows in the composite matrix
`cols`	int	The number of columns in the composite matrix

The zmk,kscan-composite node should have one child node per keyboard scan driver that should be composited. Each child node can have the following properties:

Property	Type	Description	Default
`label`	string	Unique label for the node
`kscan`	phandle	Label of the kscan driver to include
`row-offset`	int	Shifts row 0 of the included driver to a new row in the composite matrix	0
`column-offset`	int	Shifts column 0 of the included driver to a new column in the composite matrix	0

Example Configuration

For example, consider a macropad with a 3x3 matrix and two direct GPIO keys:

Matrix:

	Col 0	Col 1	Col 2
Row 0	A0	A1	A2
Row 1	A3	A4	A5
Row 2	A6	A7	A8

Direct GPIO:

	Col 0	Col 1
Row 0	B0	B1

To combine them, we need to create a composite matrix with enough rows and columns to fit both sets of keys without overlapping, then set row and/or columns offsets to shift them so they do not overlap.

One possible way to do this is a 3x4 matrix where the direct GPIO keys are shifted to below the matrix keys...

	Col 0	Col 1	Col 2
Row 0	A0	A1	A2
Row 1	A3	A4	A5
Row 2	A6	A7	A8
Row 3	B0	B1	(none)

...which can be configured with the following Devicetree code:

/ {
    chosen {
        zmk,kscan = &kscan0;
    };

    kscan0: kscan_composite {
        compatible = "zmk,kscan-composite";
        label = "KSCAN0";
        rows = <4>;
        columns = <3>;

        // Include the matrix driver
        matrix {
            kscan = <&kscan1>;
        };

        // Include the direct GPIO driver...
        direct {
            kscan = <&kscan2>;
            row-offset = <3>; // ...and shift it to not overlap
        };
    };

    kscan1: kscan_matrix {
        compatible = "zmk,kscan-gpio-matrix";
        // define 3x3 matrix here...
    };

    kscan2: kscan_direct {
        compatible = "zmk,kscan-gpio-direct";
        // define 2 direct GPIOs here...
    };
}

Mock Driver

Mock keyboard scan driver that simulates key events.

Devicetree

Applies to: compatible = "zmk,kscan-mock"

Definition file: zmk/app/dts/bindings/zmk,kscan-mock.yaml

Property	Type	Description	Default
`label`	string	Unique label for the node
`event-period`	int	Milliseconds between each generated event
`events`	array	List of key events to simulate
`rows`	int	The number of rows in the composite matrix
`cols`	int	The number of columns in the composite matrix
`exit-after`	bool	Exit the program after running all events	false

The events array should be defined using the macros from dt-bindings/zmk/kscan_mock.h.

Matrix Transform

Defines a mapping from keymap logical positions to physical matrix positions.

Transforms should be used any time the physical layout of a keyboard's keys does not match the layout of its electrical matrix and/or when not all positions in the matrix are used. This applies to most non-ortholinear boards.

Transforms can also be used for keyboards with multiple layouts. You can define multiple matrix transform nodes, one for each layout, and users can select which one they want from the /chosen node in their keymaps.

See the new shield guide for more documentation on how to define a matrix transform.

Devicetree

Applies to: compatible = "zmk,matrix-transform"

Definition file: zmk/app/dts/bindings/zmk,matrix-transform.yaml

Property	Type	Description	Default
`rows`	int	Number of rows in the transformed matrix
`columns`	int	Number of columns in the transformed matrix
`row-offset`	int	Adds an offset to all rows before looking them up in the transform	0
`col-offset`	int	Adds an offset to all columns before looking them up in the transform	0
`map`	array	A list of position transforms

The map array should be defined using the RC() macro from dt-bindings/zmk/matrix_transform.h. It should have one item per logical position in the keymap. Each item should list the physical row and column that should trigger the key in that position.

Example: Skipping Unused Positions

Any keyboard which is not a grid of 1 unit keys will likely have some unused positions in the matrix. A matrix transform can be used to skip the unused positions so users don't have to set them to &none in keymaps.

// numpad.overlay
/ {
    chosen {
        zmk,kscan = &kscan0;
        zmk,matrix_transform = &default_transform;
    };

    kscan0: kscan {
        compatible = "zmk,kscan-gpio-matrix";
        rows = <5>;
        columns = <4>;
        // define the matrix...
    };

    default_transform: matrix_transform {
        compatible = "zmk,matrix-transform";
        rows = <5>;
        columns = <4>;
        // ┌───┬───┬───┬───┐
        // │NUM│ / │ * │ - │
        // ├───┼───┼───┼───┤
        // │ 7 │ 8 │ 9 │ + │
        // ├───┼───┼───┤   │
        // │ 4 │ 5 │ 6 │   │
        // ├───┼───┼───┼───┤
        // │ 1 │ 2 │ 3 │RET│
        // ├───┴───┼───┤   │
        // │ 0     │ . │   │
        // └───────┴───┴───┘
        map = <
            RC(0,0) RC(0,1) RC(0,2) RC(0,3)
            RC(1,0) RC(1,1) RC(1,2) RC(1,3)
            RC(2,0) RC(2,1) RC(2,2)
            RC(3,0) RC(3,1) RC(3,2) RC(3,3)
            RC(4,0)         RC(4,1)
        >;
    };
};

// numpad.keymap
/ {
    keymap {
        compatible = "zmk,keymap";
        default {
            bindings = <
                &kp KP_NUM &kp KP_DIV &kp KP_MULT &kp KP_MINUS
                &kp KP_N7  &kp KP_N8  &kp KP_N9   &kp KP_PLUS
                &kp KP_N4  &kp KP_N5  &kp KP_N6
                &kp KP_N1  &kp KP_N2  &kp KP_N3   &kp KP_ENTER
                &kp KP_N0             &kp KP_DOT
            >;
        };
    }
};

Example: Non-standard Matrix

Consider a keyboard with a duplex matrix, where the matrix has twice as many rows and half as many columns as the keyboard has keys. A matrix transform can be used to correct for this so that keymaps can match the layout of the keys, not the layout of the matrix.

/ {
    chosen {
        zmk,kscan = &kscan0;
        zmk,matrix_transform = &default_transform;
    };

    kscan0: kscan {
        compatible = "zmk,kscan-gpio-matrix";
        rows = <12>;
        columns = <8>;
        // define the matrix...
    };

    default_transform: matrix_transform {
        compatible = "zmk,matrix-transform";
        rows = <6>;
        columns = <16>;
        // ESC F1 F2 F3   ...
        // `   1  2  3    ...
        // Tab  Q  W  E   ...
        // Caps  A  S  D  ...
        // Shift  Z  X  C ...
        // Ctrl Alt       ...
        map = <
            RC(0,0) RC(1,0) RC(0,1) RC(1,1)      // ...
            RC(2,0) RC(3,0) RC(2,1) RC(3,1)      // ...
            RC(4,0)   RC(5,0) RC(4,1) RC(5,1)    // ...
            RC(6,0)      RC(7,0) RC(6,1) RC(7,1) // ...
            RC(8,0)         RC(8,1) RC(9,1)      // ...
            RC(10,0) RC(11,0)                    // ...
        >;
    };
};

Common​

Kconfig​

Devicetree​

Demux Driver​

Devicetree​

Direct GPIO Driver​

Kconfig​

Devicetree​

Matrix Driver​

Devicetree​

Composite Driver​

Devicetree​

Example Configuration​

Mock Driver​

Devicetree​

Matrix Transform​

Devicetree​

Example: Skipping Unused Positions​

Example: Non-standard Matrix​

Common

Kconfig

Devicetree

Demux Driver

Devicetree

Direct GPIO Driver

Kconfig

Devicetree

Matrix Driver

Devicetree

Composite Driver

Devicetree

Example Configuration

Mock Driver

Devicetree

Matrix Transform

Devicetree

Example: Skipping Unused Positions

Example: Non-standard Matrix