Joystick

This feature provides game controller input as a joystick device supporting up to 6 axes and 32 buttons. Axes can be read either from an ADC-capable input pin, or can be virtual, so that its value is provided by your code.

An analog device such as a potentiometer found on an analog joystick's axes is based on a voltage divider, where adjusting the movable wiper controls the output voltage which can then be read by the microcontroller's ADC.

Usage

Add the following to your rules.mk:

JOYSTICK_ENABLE = yes

By default the joystick driver is analog, but you can change this with:

JOYSTICK_DRIVER = digital

Configuration

By default, two axes and eight buttons are defined, with a reported resolution of 8 bits (-127 to +127). This can be changed in your config.h:

// Min 0, max 32
#define JOYSTICK_BUTTON_COUNT 16
// Min 0, max 6: X, Y, Z, Rx, Ry, Rz
#define JOYSTICK_AXIS_COUNT 3
// Min 8, max 16
#define JOYSTICK_AXIS_RESOLUTION 10

TIP

You must define at least one button or axis. Also note that the maximum ADC resolution of the supported AVR MCUs is 10-bit, and 12-bit for most STM32 MCUs.

Axes

When defining axes for your joystick, you must provide a definition array typically in your keymap.c.

For instance, the below example configures two axes. The X axis is read from the A4 pin. With the default axis resolution of 8 bits, the range of values between 900 and 575 are scaled to -127 through 0, and values 575 to 285 are scaled to 0 through 127. The Y axis is configured as a virtual axis, and its value is not read from any pin. Instead, the user must update the axis value programmatically.

joystick_config_t joystick_axes[JOYSTICK_AXIS_COUNT] = {
    JOYSTICK_AXIS_IN(A4, 900, 575, 285),
    JOYSTICK_AXIS_VIRTUAL
};

Axes can be configured using one of the following macros:

• JOYSTICK_AXIS_IN(input_pin, low, rest, high)
  The ADC samples the provided pin. low, high and rest correspond to the minimum, maximum, and resting (or centered) analog values of the axis, respectively.
• JOYSTICK_AXIS_VIRTUAL
  No ADC reading is performed. The value should be provided by user code.

The low and high values can be swapped to effectively invert the axis.

Virtual Axes

The following example adjusts two virtual axes (X and Y) based on keypad presses, with KC_P0 as a precision modifier:

joystick_config_t joystick_axes[JOYSTICK_AXIS_COUNT] = {
    JOYSTICK_AXIS_VIRTUAL, // x
    JOYSTICK_AXIS_VIRTUAL  // y
};

static bool precision = false;
static uint16_t precision_mod = 64;
static uint16_t axis_val = 127;

bool process_record_user(uint16_t keycode, keyrecord_t *record) {
    int16_t precision_val = axis_val;
    if (precision) {
        precision_val -= precision_mod;
    }

    switch (keycode) {
        case KC_P8:
            joystick_set_axis(1, record->event.pressed ? -precision_val : 0);
            return false;
        case KC_P2:
            joystick_set_axis(1, record->event.pressed ? precision_val : 0);
            return false;
        case KC_P4:
            joystick_set_axis(0, record->event.pressed ? -precision_val : 0);
            return false;
        case KC_P6:
            joystick_set_axis(0, record->event.pressed ? precision_val : 0);
            return false;
        case KC_P0:
            precision = record->event.pressed;
            return false;
    }
    return true;
}

Keycodes

Key	Aliases	Description
QK_JOYSTICK_BUTTON_0	JS_0	Button 0
QK_JOYSTICK_BUTTON_1	JS_1	Button 1
QK_JOYSTICK_BUTTON_2	JS_2	Button 2
QK_JOYSTICK_BUTTON_3	JS_3	Button 3
QK_JOYSTICK_BUTTON_4	JS_4	Button 4
QK_JOYSTICK_BUTTON_5	JS_5	Button 5
QK_JOYSTICK_BUTTON_6	JS_6	Button 6
QK_JOYSTICK_BUTTON_7	JS_7	Button 7
QK_JOYSTICK_BUTTON_8	JS_8	Button 8
QK_JOYSTICK_BUTTON_9	JS_9	Button 9
QK_JOYSTICK_BUTTON_10	JS_10	Button 10
QK_JOYSTICK_BUTTON_11	JS_11	Button 11
QK_JOYSTICK_BUTTON_12	JS_12	Button 12
QK_JOYSTICK_BUTTON_13	JS_13	Button 13
QK_JOYSTICK_BUTTON_14	JS_14	Button 14
QK_JOYSTICK_BUTTON_15	JS_15	Button 15
QK_JOYSTICK_BUTTON_16	JS_16	Button 16
QK_JOYSTICK_BUTTON_17	JS_17	Button 17
QK_JOYSTICK_BUTTON_18	JS_18	Button 18
QK_JOYSTICK_BUTTON_19	JS_19	Button 19
QK_JOYSTICK_BUTTON_20	JS_20	Button 20
QK_JOYSTICK_BUTTON_21	JS_21	Button 21
QK_JOYSTICK_BUTTON_22	JS_22	Button 22
QK_JOYSTICK_BUTTON_23	JS_23	Button 23
QK_JOYSTICK_BUTTON_24	JS_24	Button 24
QK_JOYSTICK_BUTTON_25	JS_25	Button 25
QK_JOYSTICK_BUTTON_26	JS_26	Button 26
QK_JOYSTICK_BUTTON_27	JS_27	Button 27
QK_JOYSTICK_BUTTON_28	JS_28	Button 28
QK_JOYSTICK_BUTTON_29	JS_29	Button 29
QK_JOYSTICK_BUTTON_30	JS_30	Button 30
QK_JOYSTICK_BUTTON_31	JS_31	Button 31

API

struct joystick_t

Contains the state of the joystick.

Members

• uint8_t buttons[]
  A bit-packed array containing the joystick button states. The size is calculated as (JOYSTICK_BUTTON_COUNT - 1) / 8 + 1.
• int16_t axes[]
  An array of analog values for each defined axis.
• bool dirty
  Whether the current state needs to be sent to the host.

---

struct joystick_config_t

Describes a single axis.

Members

• pin_t input_pin
  The pin to read the analog value from, or JS_VIRTUAL_AXIS.
• uint16_t min_digit
  The minimum analog value.
• uint16_t mid_digit
  The resting or midpoint analog value.
• uint16_t max_digit
  The maximum analog value.

---

void joystick_flush(void)

Send the joystick report to the host, if it has been marked as dirty.

---

void register_joystick_button(uint8_t button)

Set the state of a button, and flush the report.

Arguments

• uint8_t button
  The index of the button to press, from 0 to 31.

---

void unregister_joystick_button(uint8_t button)

Reset the state of a button, and flush the report.

Arguments

• uint8_t button
  The index of the button to release, from 0 to 31.

---

int16_t joystick_read_axis(uint8_t axis)

Sample and process the analog value of the given axis.

Arguments

• uint8_t axis
  The axis to read.

Return Value

A signed 16-bit integer, where 0 is the resting or mid point.

void joystick_set_axis(uint8_t axis, int16_t value)

Set the value of the given axis.

Arguments

• uint8_t axis
  The axis to set the value of.
• int16_t value
  The value to set.