cmdr-keyboard/rp2040/src/button_matrix.rs

//! Button matrix scanner for CMDR Keyboard 42
//!
//! Ported from the joystick firmware for consistent behaviour and structure.
//! Scans a row/column matrix and produces a debounced boolean state for each
//! button using per-button counters and small inter-column delays.

use core::convert::Infallible;
use cortex_m::delay::Delay;
use embedded_hal::digital::{InputPin, OutputPin};

/// Row/column scanned button matrix driver with debounce counters.
pub struct ButtonMatrix<'a, const R: usize, const C: usize, const N: usize> {
    rows: &'a mut [&'a mut dyn InputPin<Error = Infallible>; R],
    cols: &'a mut [&'a mut dyn OutputPin<Error = Infallible>; C],
    pressed: [bool; N],
    press_threshold: u8,
    release_threshold: u8,
    debounce_counter: [u8; N],
    // Additional protection: minimum time between same-key presses
    last_press_scan: [u32; N],
    scan_counter: u32,
}

impl<'a, const R: usize, const C: usize, const N: usize> ButtonMatrix<'a, R, C, N> {
    pub fn new(
        rows: &'a mut [&'a mut dyn InputPin<Error = Infallible>; R],
        cols: &'a mut [&'a mut dyn OutputPin<Error = Infallible>; C],
        press_threshold: u8,
        release_threshold: u8,
    ) -> Self {
        Self {
            rows,
            cols,
            pressed: [false; N],
            press_threshold,
            release_threshold,
            debounce_counter: [0; N],
            last_press_scan: [0; N],
            scan_counter: 0,
        }
    }

    pub fn init_pins(&mut self) {
        for col in self.cols.iter_mut() {
            col.set_high().unwrap();
        }
    }

    pub fn scan_matrix(&mut self, delay: &mut Delay) {
        self.scan_counter = self.scan_counter.wrapping_add(1);
        for col_index in 0..self.cols.len() {
            self.cols[col_index].set_low().unwrap();
            delay.delay_us(1);
            self.process_column(col_index);
            self.cols[col_index].set_high().unwrap();
            delay.delay_us(1);
        }
    }

    fn process_column(&mut self, col_index: usize) {
        for row_index in 0..self.rows.len() {
            let button_index: usize = col_index + (row_index * C);
            let current_state = self.rows[row_index].is_low().unwrap();

            if current_state == self.pressed[button_index] {
                self.debounce_counter[button_index] = 0;
                continue;
            }

            self.debounce_counter[button_index] =
                self.debounce_counter[button_index].saturating_add(1);

            let threshold = if current_state {
                self.press_threshold
            } else {
                self.release_threshold
            };

            if self.debounce_counter[button_index] >= threshold {
                // Additional protection for press events: minimum 20 scans (5ms) between presses
                if current_state { // Pressing
                    let scans_since_last = self.scan_counter.wrapping_sub(self.last_press_scan[button_index]);
                    if scans_since_last >= 20 { // 5ms at 250μs scan rate
                        self.pressed[button_index] = current_state;
                        self.last_press_scan[button_index] = self.scan_counter;
                    }
                } else { // Releasing
                    self.pressed[button_index] = current_state;
                }
                self.debounce_counter[button_index] = 0;
            }
        }
    }

    pub fn buttons_pressed(&mut self) -> [bool; N] {
        self.pressed
    }
}

#[cfg(all(test, feature = "std"))]
mod tests {
    use super::*;
    use core::cell::Cell;
    use embedded_hal::digital::ErrorType;
    use std::rc::Rc;

    struct MockInputPin {
        state: Rc<Cell<bool>>,
    }

    impl MockInputPin {
        fn new(state: Rc<Cell<bool>>) -> Self {
            Self { state }
        }
    }

    impl ErrorType for MockInputPin {
        type Error = Infallible;
    }

    impl InputPin for MockInputPin {
        fn is_high(&mut self) -> Result<bool, Self::Error> {
            Ok(!self.state.get())
        }

        fn is_low(&mut self) -> Result<bool, Self::Error> {
            Ok(self.state.get())
        }
    }

    struct MockOutputPin {
        state: Rc<Cell<bool>>,
    }

    impl MockOutputPin {
        fn new(state: Rc<Cell<bool>>) -> Self {
            Self { state }
        }
    }

    impl ErrorType for MockOutputPin {
        type Error = Infallible;
    }

    impl OutputPin for MockOutputPin {
        fn set_high(&mut self) -> Result<(), Self::Error> {
            self.state.set(true);
            Ok(())
        }

        fn set_low(&mut self) -> Result<(), Self::Error> {
            self.state.set(false);
            Ok(())
        }
    }

    fn matrix_fixture() -> (
        ButtonMatrix<'static, 1, 1, 1>,
        Rc<Cell<bool>>,
        Rc<Cell<bool>>,
    ) {
        let row_state = Rc::new(Cell::new(false));
        let col_state = Rc::new(Cell::new(false));

        let row_pin: &'static mut dyn InputPin<Error = Infallible> =
            Box::leak(Box::new(MockInputPin::new(row_state.clone())));
        let col_pin: &'static mut dyn OutputPin<Error = Infallible> =
            Box::leak(Box::new(MockOutputPin::new(col_state.clone())));

        let rows: &'static mut [&'static mut dyn InputPin<Error = Infallible>; 1] =
            Box::leak(Box::new([row_pin]));
        let cols: &'static mut [&'static mut dyn OutputPin<Error = Infallible>; 1] =
            Box::leak(Box::new([col_pin]));

        let matrix = ButtonMatrix::new(rows, cols, 5, 5);

        (matrix, row_state, col_state)
    }

    #[test]
    fn init_sets_columns_high() {
        let (mut matrix, _row_state, col_state) = matrix_fixture();
        assert!(!col_state.get());
        matrix.init_pins();
        assert!(col_state.get());
    }

    #[test]
    fn debounce_respects_threshold() {
        let (mut matrix, row_state, _col_state) = matrix_fixture();
        let mut states = matrix.buttons_pressed();
        assert!(!states[0]);

        // Set scan counter to start with enough history
        matrix.scan_counter = 100;

        row_state.set(true);
        // Need 5 scans to register press
        for _ in 0..4 {
            matrix.scan_counter = matrix.scan_counter.wrapping_add(1);
            matrix.process_column(0);
            states = matrix.buttons_pressed();
            assert!(!states[0]); // Still not pressed
        }
        matrix.scan_counter = matrix.scan_counter.wrapping_add(1);
        matrix.process_column(0); // 5th scan
        states = matrix.buttons_pressed();
        assert!(states[0]); // Now pressed

        row_state.set(false);
        // Need 5 scans to register release
        for _ in 0..4 {
            matrix.scan_counter = matrix.scan_counter.wrapping_add(1);
            matrix.process_column(0);
            states = matrix.buttons_pressed();
            assert!(states[0]); // Still pressed
        }
        matrix.scan_counter = matrix.scan_counter.wrapping_add(1);
        matrix.process_column(0); // 5th scan
        states = matrix.buttons_pressed();
        assert!(!states[0]); // Now released
    }
}