skylark-qmk/docs/feature_joystick.md

Joystick :id=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 :id=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 :id=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

?> 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 :id=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_AXES_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_IN_OUT(input_pin, output_pin, low, rest, high)
  Same as JOYSTICK_AXIS_IN(), but the provided output_pin will be pulled high before input_pin is read.
• JOYSTICK_AXIS_IN_OUT_GROUND(input_pin, output_pin, ground_pin, low, rest, high)
  Same as JOYSTICK_AXIS_IN_OUT(), but the provided ground_pin will be pulled low before reading from input_pin.
• 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 :id=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_AXES_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 :id=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 :id=api

struct joystick_t :id=api-joystick-t

Contains the state of the joystick.

Members :id=api-joystick-t-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 :id=api-joystick-config-t

Describes a single axis.

Members :id=api-joystick-config-t-members

• pin_t output_pin
  A pin to set as output high when reading the analog value, or JS_VIRTUAL_AXIS.
• pin_t input_pin
  The pin to read the analog value from, or JS_VIRTUAL_AXIS.
• pin_t ground_pin
  A pin to set as output low when reading the analog value, 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) :id=api-joystick-flush

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

---

void register_joystick_button(uint8_t button) :id=api-register-joystick-button

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

Arguments :id=api-register-joystick-button-arguments

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

---

void register_joystick_button(uint8_t button) :id=api-unregister-joystick-button

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

Arguments :id=api-unregister-joystick-button-arguments

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

---

int16_t joystick_read_axis(uint8_t axis) :id=api-joystick-read-axis

Sample and process the analog value of the given axis.

Arguments :id=api-joystick-read-axis-arguments

• uint8_t axis
  The axis to read.

Return Value :id=api-joystick-read-axis-return

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

void joystick_set_axis(uint8_t axis, int16_t value) :id=api-joystick-set-axis

Set the value of the given axis.

Arguments :id=api-joystick-set-axis-arguments

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