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      • Joysticks

      A joystick controls the mouse pointer through analog inputs. Configuration through keyboard.toml supports nRF52 chips with an SAADC peripheral. Use a debug probe to calibrate the joystick for your hardware.

      TOML configuration

      Add one entry per joystick to keyboard.toml:

      [[input_device.joystick]]
name = "default"
# id = 0
pin_x = "P0_31"
pin_y = "P0_29"
pin_z = "_"
transform = [[80, 0], [0, 80]]
bias = [29130, 29365]
resolution = 6
      FieldDescription
      nameUnique joystick name.
      idDevice ID matched by JoystickProcessor. Defaults to sequential IDs starting at 0.
      pin_x, pin_y, pin_zADC pins in axis order. Use _ for an unused Z axis.
      biasOffset added to each axis to center its resting value at zero.
      transformDivisors mapping input axes (columns) to output axes (rows). A zero entry ignores that contribution.
      resolutionPositive movement step used to reduce small fluctuations. Values are rounded toward zero to multiples of this step.

      Match the dimensions of bias and transform to the number of configured axes. The example uses two axes; larger positive diagonal divisors reduce pointer speed.

      Calibration

      1. For the two-axis example, start with bias = [0, 0], transform = [[1, 0], [0, 1]], and resolution = 1.
      2. Enable debug logging and read JoystickProcessor::generate_report: record = [...] with the joystick released. Set each bias to the negative of that axis's resting value.
      3. Increase the diagonal transform values to reduce pointer speed.
      4. Increase resolution if the pointer jitters at rest.

      Sampling

      RMK reads the configured axes in one ADC scan. After 1.2 seconds without significant changes between consecutive joystick samples, it uses the idle interval. Battery voltage changes do not trigger fast joystick sampling. When battery measurement shares the ADC with a joystick, battery voltage is reported at most once every 30 seconds.

      Rust configuration

      Use one NrfAdc for the joystick and battery channels. In your firmware initialization, list events in ADC channel order and match the joystick device ID to its processor. This example assumes p, matrix, and keymap are already initialized.

      polling_interval sets the active scan interval. light_sleep sets the initial and idle interval; None uses polling_interval throughout.

      use embassy_nrf::saadc::{self, Input as _};
use embassy_time::Duration;
use rmk::input_device::{
    adc::{AnalogEventType, NrfAdc},
    battery::BatteryProcessor,
    joystick::JoystickProcessor,
};

embassy_nrf::bind_interrupts!(struct AdcIrqs {
    SAADC => saadc::InterruptHandler;
});

let saadc_config = saadc::Config::default();
let adc = saadc::Saadc::new(p.SAADC, AdcIrqs, saadc_config,
    [
        saadc::ChannelConfig::single_ended(saadc::VddhDiv5Input.degrade_saadc()),
        saadc::ChannelConfig::single_ended(p.P0_31.degrade_saadc()),
        saadc::ChannelConfig::single_ended(p.P0_29.degrade_saadc())
    ],
);
adc.calibrate().await;
let mut adc_dev = NrfAdc::new(
    adc,
    [AnalogEventType::Battery, AnalogEventType::Joystick(2)],
    [0, 0], // device id per event; unused for battery events
    Duration::from_millis(20), // polling interval
    Some(Duration::from_millis(350)), // light sleep interval
);
let mut batt_proc = BatteryProcessor::new(1, 5);
let mut joy_proc = JoystickProcessor::new(0, [[80, 0], [0, 80]], [29130, 29365], 6, &keymap);
rmk::run_all!(matrix, adc_dev, joy_proc, batt_proc).await;