Add 0x09_dht11_rust: DHT11 temperature/humidity sensor driver

drivers/0x09_dht11_rust/src/board.rs

@@ -0,0 +1,385 @@
+//! @file board.rs
+//! @brief Board-level HAL helpers for the DHT11 driver
+//! @author Kevin Thomas
+//! @date 2025
+//!
+//! MIT License
+//!
+//! Copyright (c) 2025 Kevin Thomas
+//!
+//! Permission is hereby granted, free of charge, to any person obtaining a copy
+//! of this software and associated documentation files (the "Software"), to deal
+//! in the Software without restriction, including without limitation the rights
+//! to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//! copies of the Software, and to permit persons to whom the Software is
+//! furnished to do so, subject to the following conditions:
+//!
+//! The above copyright notice and this permission notice shall be included in
+//! all copies or substantial portions of the Software.
+//!
+//! THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//! IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//! FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//! AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//! LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//! OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//! SOFTWARE.
+
+// DHT11 pure-logic functions (checksum, parsing, formatting)
+use crate::dht11;
+// Rate extension trait for .Hz() baud rate construction
+use fugit::RateExtU32;
+// Clock trait for accessing system clock frequency
+use hal::Clock;
+// GPIO pin types and function selectors
+use hal::gpio::{FunctionNull, FunctionUart, Pin, PullDown, PullNone};
+// UART configuration and peripheral types
+use hal::uart::{DataBits, Enabled, StopBits, UartConfig, UartPeripheral};
+
+// Alias our HAL crate
+#[cfg(rp2350)]
+use rp235x_hal as hal;
+#[cfg(rp2040)]
+use rp2040_hal as hal;
+
+// Timer device type for the HAL timer peripheral
+#[cfg(rp2350)]
+pub(crate) type HalTimer = hal::Timer<hal::timer::CopyableTimer0>;
+// Timer type alias for RP2040 (non-generic)
+#[cfg(rp2040)]
+pub(crate) type HalTimer = hal::Timer;
+
+/// External crystal frequency in Hz (12 MHz).
+pub(crate) const XTAL_FREQ_HZ: u32 = 12_000_000u32;
+
+/// UART baud rate in bits per second.
+pub(crate) const UART_BAUD: u32 = 115_200;
+
+/// GPIO pin number connected to the DHT11 data line.
+pub(crate) const DHT11_GPIO: u8 = 4;
+
+/// Polling interval in milliseconds (DHT11 minimum is 2 seconds).
+pub(crate) const POLL_MS: u32 = 2_000;
+
+/// Type alias for the configured TX pin (GPIO 0, UART function, no pull).
+pub(crate) type TxPin = Pin<hal::gpio::bank0::Gpio0, FunctionUart, PullNone>;
+
+/// Type alias for the configured RX pin (GPIO 1, UART function, no pull).
+pub(crate) type RxPin = Pin<hal::gpio::bank0::Gpio1, FunctionUart, PullNone>;
+
+/// Type alias for the default TX pin state from `Pins::new()`.
+pub(crate) type TxPinDefault = Pin<hal::gpio::bank0::Gpio0, FunctionNull, PullDown>;
+
+/// Type alias for the default RX pin state from `Pins::new()`.
+pub(crate) type RxPinDefault = Pin<hal::gpio::bank0::Gpio1, FunctionNull, PullDown>;
+
+/// Type alias for the fully-enabled UART0 peripheral with TX/RX pins.
+pub(crate) type EnabledUart = UartPeripheral<Enabled, hal::pac::UART0, (TxPin, RxPin)>;
+
+/// Initialise system clocks and PLLs from the external 12 MHz crystal.
+///
+/// # Arguments
+///
+/// * `xosc` - XOSC peripheral singleton.
+/// * `clocks` - CLOCKS peripheral singleton.
+/// * `pll_sys` - PLL_SYS peripheral singleton.
+/// * `pll_usb` - PLL_USB peripheral singleton.
+/// * `resets` - Mutable reference to the RESETS peripheral.
+/// * `watchdog` - Mutable reference to the watchdog timer.
+///
+/// # Returns
+///
+/// Configured clocks manager.
+///
+/// # Panics
+///
+/// Panics if clock initialisation fails.
+pub(crate) fn init_clocks(
+    xosc: hal::pac::XOSC,
+    clocks: hal::pac::CLOCKS,
+    pll_sys: hal::pac::PLL_SYS,
+    pll_usb: hal::pac::PLL_USB,
+    resets: &mut hal::pac::RESETS,
+    watchdog: &mut hal::Watchdog,
+) -> hal::clocks::ClocksManager {
+    hal::clocks::init_clocks_and_plls(
+        XTAL_FREQ_HZ, xosc, clocks, pll_sys, pll_usb, resets, watchdog,
+    )
+    .unwrap()
+}
+
+/// Unlock the GPIO bank and return the pin set.
+///
+/// # Arguments
+///
+/// * `io_bank0` - IO_BANK0 peripheral singleton.
+/// * `pads_bank0` - PADS_BANK0 peripheral singleton.
+/// * `sio` - SIO peripheral singleton.
+/// * `resets` - Mutable reference to the RESETS peripheral.
+///
+/// # Returns
+///
+/// GPIO pin set for the entire bank.
+pub(crate) fn init_pins(
+    io_bank0: hal::pac::IO_BANK0,
+    pads_bank0: hal::pac::PADS_BANK0,
+    sio: hal::pac::SIO,
+    resets: &mut hal::pac::RESETS,
+) -> hal::gpio::Pins {
+    let sio = hal::Sio::new(sio);
+    hal::gpio::Pins::new(io_bank0, pads_bank0, sio.gpio_bank0, resets)
+}
+
+/// Initialise UART0 for serial output (stdio equivalent).
+///
+/// # Arguments
+///
+/// * `uart0` - PAC UART0 peripheral singleton.
+/// * `tx_pin` - GPIO pin to use as UART0 TX (GPIO 0).
+/// * `rx_pin` - GPIO pin to use as UART0 RX (GPIO 1).
+/// * `resets` - Mutable reference to the RESETS peripheral.
+/// * `clocks` - Reference to the initialised clock configuration.
+///
+/// # Returns
+///
+/// Enabled UART0 peripheral ready for blocking writes.
+///
+/// # Panics
+///
+/// Panics if the HAL cannot achieve the requested baud rate.
+pub(crate) fn init_uart(
+    uart0: hal::pac::UART0,
+    tx_pin: TxPinDefault,
+    rx_pin: RxPinDefault,
+    resets: &mut hal::pac::RESETS,
+    clocks: &hal::clocks::ClocksManager,
+) -> EnabledUart {
+    let pins = (
+        tx_pin.reconfigure::<FunctionUart, PullNone>(),
+        rx_pin.reconfigure::<FunctionUart, PullNone>(),
+    );
+    let cfg = UartConfig::new(UART_BAUD.Hz(), DataBits::Eight, None, StopBits::One);
+    UartPeripheral::new(uart0, pins, resets)
+        .enable(cfg, clocks.peripheral_clock.freq())
+        .unwrap()
+}
+
+/// Create a blocking delay timer from the ARM SysTick peripheral.
+///
+/// # Arguments
+///
+/// * `clocks` - Reference to the initialised clock configuration.
+///
+/// # Returns
+///
+/// Blocking delay provider.
+///
+/// # Panics
+///
+/// Panics if the cortex-m core peripherals have already been taken.
+pub(crate) fn init_delay(clocks: &hal::clocks::ClocksManager) -> cortex_m::delay::Delay {
+    let core = cortex_m::Peripherals::take().unwrap();
+    cortex_m::delay::Delay::new(core.SYST, clocks.system_clock.freq().to_Hz())
+}
+
+/// Drive the DHT11 data pin to a given level (enables output).
+///
+/// # Arguments
+///
+/// * `high` - `true` to drive HIGH, `false` to drive LOW.
+fn gpio_drive(high: bool) {
+    unsafe {
+        let sio = &*hal::pac::SIO::PTR;
+        if high {
+            sio.gpio_out_set().write(|w| w.bits(1u32 << DHT11_GPIO));
+        } else {
+            sio.gpio_out_clr().write(|w| w.bits(1u32 << DHT11_GPIO));
+        }
+        sio.gpio_oe_set().write(|w| w.bits(1u32 << DHT11_GPIO));
+    }
+}
+
+/// Release the DHT11 data pin back to input mode (disable output driver).
+fn gpio_release() {
+    unsafe {
+        let sio = &*hal::pac::SIO::PTR;
+        sio.gpio_oe_clr().write(|w| w.bits(1u32 << DHT11_GPIO));
+    }
+}
+
+/// Read the current logic level of the DHT11 data pin.
+///
+/// # Returns
+///
+/// `true` if the pin reads HIGH, `false` if LOW.
+fn gpio_read() -> bool {
+    unsafe { (*hal::pac::SIO::PTR).gpio_in().read().bits() & (1u32 << DHT11_GPIO) != 0 }
+}
+
+/// Read the free-running microsecond timer (lower 32 bits).
+///
+/// # Arguments
+///
+/// * `timer` - Reference to the HAL timer peripheral.
+///
+/// # Returns
+///
+/// Current timer value in microseconds (wrapping at 2^32).
+fn time_us_32(timer: &HalTimer) -> u32 {
+    timer.get_counter().ticks() as u32
+}
+
+/// Send the DHT11 start signal on the data pin.
+///
+/// Drives the pin LOW for 18 ms then HIGH for 40 us before switching
+/// the pin to input mode to listen for the sensor response.
+///
+/// # Arguments
+///
+/// * `delay` - Mutable reference to the blocking delay provider.
+fn send_start_signal(delay: &mut cortex_m::delay::Delay) {
+    gpio_drive(false);
+    delay.delay_ms(18);
+    gpio_drive(true);
+    delay.delay_us(40);
+    gpio_release();
+}
+
+/// Spin until the pin leaves the given logic level, or time out.
+///
+/// # Arguments
+///
+/// * `level` - Logic level to wait through (`true` = HIGH, `false` = LOW).
+///
+/// # Returns
+///
+/// `true` once the level changed, `false` on timeout.
+fn wait_for_level(level: bool) -> bool {
+    let mut timeout: u32 = dht11::LEVEL_WAIT_TIMEOUT;
+    while gpio_read() == level {
+        timeout -= 1;
+        if timeout == 0 {
+            return false;
+        }
+    }
+    true
+}
+
+/// Wait for the DHT11 response after the start signal.
+///
+/// The sensor pulls LOW then HIGH then LOW again; each transition
+/// is awaited with a timeout.
+///
+/// # Returns
+///
+/// `true` if the full response was received, `false` on timeout.
+fn wait_response() -> bool {
+    wait_for_level(true) && wait_for_level(false) && wait_for_level(true)
+}
+
+/// Read a single bit from the DHT11 data stream.
+///
+/// Waits for the low-period to end, measures the high-period duration,
+/// and accumulates the result into the data array via
+/// [`dht11::accumulate_bit`].
+///
+/// # Arguments
+///
+/// * `data` - 5-byte array accumulating the received bits.
+/// * `i` - Bit index (0–39).
+/// * `timer` - Reference to the HAL timer for microsecond measurement.
+///
+/// # Returns
+///
+/// `true` on success, `false` on timeout.
+fn read_bit(data: &mut [u8; 5], i: usize, timer: &HalTimer) -> bool {
+    if !wait_for_level(false) {
+        return false;
+    }
+    let start = time_us_32(timer);
+    if !wait_for_level(true) {
+        return false;
+    }
+    let duration = time_us_32(timer).wrapping_sub(start);
+    dht11::accumulate_bit(data, i, duration);
+    true
+}
+
+/// Read all 40 data bits from the DHT11.
+///
+/// # Arguments
+///
+/// * `data` - 5-byte array filled with the received data.
+/// * `timer` - Reference to the HAL timer for microsecond measurement.
+///
+/// # Returns
+///
+/// `true` if all 40 bits were read, `false` on timeout.
+fn read_40_bits(data: &mut [u8; 5], timer: &HalTimer) -> bool {
+    for i in 0..40 {
+        if !read_bit(data, i, timer) {
+            return false;
+        }
+    }
+    true
+}
+
+/// Execute the full DHT11 read protocol.
+///
+/// Sends the start signal, waits for the sensor response, reads 40 bits
+/// of data, validates the checksum, and parses humidity and temperature.
+///
+/// # Arguments
+///
+/// * `timer` - Reference to the HAL timer for microsecond measurement.
+/// * `delay` - Mutable reference to the blocking delay provider.
+///
+/// # Returns
+///
+/// `Some((humidity, temperature))` on success, `None` on failure.
+pub(crate) fn read_sensor(
+    timer: &HalTimer,
+    delay: &mut cortex_m::delay::Delay,
+) -> Option<(f32, f32)> {
+    let mut data = [0u8; 5];
+    send_start_signal(delay);
+    if !wait_response() {
+        return None;
+    }
+    if !read_40_bits(&mut data, timer) {
+        return None;
+    }
+    if !dht11::validate_checksum(&data) {
+        return None;
+    }
+    Some((dht11::parse_humidity(&data), dht11::parse_temperature(&data)))
+}
+
+/// Read the sensor, format the result, write it over UART, and wait.
+///
+/// On a successful read, prints humidity and temperature; on failure,
+/// prints a wiring-check message. Always waits [`POLL_MS`] before
+/// returning to respect the DHT11 minimum polling interval.
+///
+/// # Arguments
+///
+/// * `uart` - Reference to the enabled UART peripheral for serial output.
+/// * `timer` - Reference to the HAL timer for microsecond measurement.
+/// * `delay` - Mutable reference to the blocking delay provider.
+pub(crate) fn poll_sensor(
+    uart: &EnabledUart,
+    timer: &HalTimer,
+    delay: &mut cortex_m::delay::Delay,
+) {
+    let mut buf = [0u8; 64];
+    let n = match read_sensor(timer, delay) {
+        Some((h, t)) => dht11::format_reading(&mut buf, h, t),
+        None => dht11::format_error(&mut buf, DHT11_GPIO),
+    };
+    buf[n] = b'\r';
+    buf[n + 1] = b'\n';
+    uart.write_full_blocking(&buf[..n + 2]);
+    delay.delay_ms(POLL_MS);
+}
+
+// End of file

drivers/0x09_dht11_rust/src/dht11.rs

@@ -0,0 +1,343 @@
+//! @file dht11.rs
+//! @brief Implementation of DHT11 temperature and humidity sensor driver
+//! @author Kevin Thomas
+//! @date 2025
+//!
+//! MIT License
+//!
+//! Copyright (c) 2025 Kevin Thomas
+//!
+//! Permission is hereby granted, free of charge, to any person obtaining a copy
+//! of this software and associated documentation files (the "Software"), to deal
+//! in the Software without restriction, including without limitation the rights
+//! to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//! copies of the Software, and to permit persons to whom the Software is
+//! furnished to do so, subject to the following conditions:
+//!
+//! The above copyright notice and this permission notice shall be included in
+//! all copies or substantial portions of the Software.
+//!
+//! THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//! IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//! FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//! AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//! LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//! OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//! SOFTWARE.
+
+/// Bit-duration threshold in microseconds.
+///
+/// If the high pulse is longer than this value, the bit is a 1; otherwise 0.
+pub const BIT_THRESHOLD_US: u32 = 40;
+
+/// Timeout in spin-loop iterations for waiting on a pin level change.
+pub const LEVEL_WAIT_TIMEOUT: u32 = 10_000;
+
+/// Accumulate a single received bit into the 5-byte data array.
+///
+/// Shifts `data[byte_index]` left by one and sets the LSB to 1 if the
+/// measured high-pulse `duration_us` exceeds [`BIT_THRESHOLD_US`].
+///
+/// # Arguments
+///
+/// * `data` - 5-byte array accumulating the received bits.
+/// * `bit_index` - Bit index (0..39).
+/// * `duration_us` - Measured duration of the high pulse in microseconds.
+pub fn accumulate_bit(data: &mut [u8; 5], bit_index: usize, duration_us: u32) {
+    let byte = bit_index / 8;
+    data[byte] <<= 1;
+    if duration_us > BIT_THRESHOLD_US {
+        data[byte] |= 1;
+    }
+}
+
+/// Verify the DHT11 checksum byte.
+///
+/// The checksum (byte 4) must equal the lower 8 bits of the sum of
+/// bytes 0 through 3.
+///
+/// # Arguments
+///
+/// * `data` - 5-byte received data (bytes 0–3 plus checksum in byte 4).
+///
+/// # Returns
+///
+/// `true` if the checksum matches, `false` otherwise.
+pub fn validate_checksum(data: &[u8; 5]) -> bool {
+    data[4] == (data[0].wrapping_add(data[1]).wrapping_add(data[2]).wrapping_add(data[3]))
+}
+
+/// Parse humidity from the raw DHT11 data bytes.
+///
+/// Humidity is encoded as an integer part in byte 0 and a fractional
+/// part (tenths) in byte 1.
+///
+/// # Arguments
+///
+/// * `data` - 5-byte received data.
+///
+/// # Returns
+///
+/// Humidity as a percentage (e.g. 65.3 for 65.3%).
+pub fn parse_humidity(data: &[u8; 5]) -> f32 {
+    data[0] as f32 + data[1] as f32 * 0.1
+}
+
+/// Parse temperature from the raw DHT11 data bytes.
+///
+/// Temperature is encoded as an integer part in byte 2 and a fractional
+/// part (tenths) in byte 3.
+///
+/// # Arguments
+///
+/// * `data` - 5-byte received data.
+///
+/// # Returns
+///
+/// Temperature in degrees Celsius.
+pub fn parse_temperature(data: &[u8; 5]) -> f32 {
+    data[2] as f32 + data[3] as f32 * 0.1
+}
+
+/// Format a sensor reading as `"Humidity: XX.X%  Temperature: XX.X C"`.
+///
+/// # Arguments
+///
+/// * `buf` - Mutable byte slice (must be at least 40 bytes).
+/// * `humidity` - Humidity percentage.
+/// * `temperature` - Temperature in degrees Celsius.
+///
+/// # Returns
+///
+/// Number of bytes written into the buffer.
+pub fn format_reading(buf: &mut [u8], humidity: f32, temperature: f32) -> usize {
+    let mut pos = 0;
+    let prefix = b"Humidity: ";
+    buf[pos..pos + prefix.len()].copy_from_slice(prefix);
+    pos += prefix.len();
+    pos += format_f32_1(&mut buf[pos..], humidity);
+    let mid = b"%  Temperature: ";
+    buf[pos..pos + mid.len()].copy_from_slice(mid);
+    pos += mid.len();
+    pos += format_f32_1(&mut buf[pos..], temperature);
+    let suffix = b" C";
+    buf[pos..pos + suffix.len()].copy_from_slice(suffix);
+    pos += suffix.len();
+    pos
+}
+
+/// Format a failed-read error message.
+///
+/// # Arguments
+///
+/// * `buf` - Mutable byte slice (must be at least 42 bytes).
+/// * `gpio` - GPIO pin number to include in the message.
+///
+/// # Returns
+///
+/// Number of bytes written into the buffer.
+pub fn format_error(buf: &mut [u8], gpio: u8) -> usize {
+    let mut pos = 0;
+    let prefix = b"DHT11 read failed - check wiring on GPIO ";
+    buf[pos..pos + prefix.len()].copy_from_slice(prefix);
+    pos += prefix.len();
+    pos += format_u8(&mut buf[pos..], gpio);
+    pos
+}
+
+/// Format a `u8` as decimal ASCII digits.
+///
+/// # Arguments
+///
+/// * `buf` - Output buffer.
+/// * `val` - Value to format.
+///
+/// # Returns
+///
+/// Number of bytes written.
+fn format_u8(buf: &mut [u8], val: u8) -> usize {
+    if val >= 100 {
+        buf[0] = b'0' + val / 100;
+        buf[1] = b'0' + (val / 10) % 10;
+        buf[2] = b'0' + val % 10;
+        3
+    } else if val >= 10 {
+        buf[0] = b'0' + val / 10;
+        buf[1] = b'0' + val % 10;
+        2
+    } else {
+        buf[0] = b'0' + val;
+        1
+    }
+}
+
+/// Format an `f32` with one decimal place (e.g. `"25.3"`).
+///
+/// # Arguments
+///
+/// * `buf` - Output buffer.
+/// * `val` - Value to format.
+///
+/// # Returns
+///
+/// Number of bytes written.
+fn format_f32_1(buf: &mut [u8], val: f32) -> usize {
+    let scaled = (val * 10.0) as u32;
+    let integer = scaled / 10;
+    let frac = (scaled % 10) as u8;
+    let mut pos = 0;
+    if integer >= 100 {
+        buf[pos] = b'0' + (integer / 100) as u8;
+        pos += 1;
+    }
+    if integer >= 10 {
+        buf[pos] = b'0' + ((integer / 10) % 10) as u8;
+        pos += 1;
+    }
+    buf[pos] = b'0' + (integer % 10) as u8;
+    pos += 1;
+    buf[pos] = b'.';
+    pos += 1;
+    buf[pos] = b'0' + frac;
+    pos += 1;
+    pos
+}
+
+#[cfg(test)]
+mod tests {
+    // Import all parent module items
+    use super::*;
+
+    #[test]
+    fn accumulate_bit_zero_short_pulse() {
+        let mut data = [0u8; 5];
+        accumulate_bit(&mut data, 0, 30);
+        assert_eq!(data[0], 0);
+    }
+
+    #[test]
+    fn accumulate_bit_one_long_pulse() {
+        let mut data = [0u8; 5];
+        accumulate_bit(&mut data, 0, 70);
+        assert_eq!(data[0], 1);
+    }
+
+    #[test]
+    fn accumulate_bit_threshold_exact() {
+        let mut data = [0u8; 5];
+        accumulate_bit(&mut data, 0, BIT_THRESHOLD_US);
+        assert_eq!(data[0], 0);
+    }
+
+    #[test]
+    fn accumulate_bit_two_bits() {
+        let mut data = [0u8; 5];
+        accumulate_bit(&mut data, 0, 70);
+        accumulate_bit(&mut data, 1, 30);
+        assert_eq!(data[0], 0b10);
+    }
+
+    #[test]
+    fn accumulate_bit_crosses_byte() {
+        let mut data = [0u8; 5];
+        accumulate_bit(&mut data, 7, 70);
+        accumulate_bit(&mut data, 8, 70);
+        assert_eq!(data[0], 1);
+        assert_eq!(data[1], 1);
+    }
+
+    #[test]
+    fn validate_checksum_valid() {
+        let data = [0x28, 0x00, 0x1A, 0x00, 0x42];
+        assert!(validate_checksum(&data));
+    }
+
+    #[test]
+    fn validate_checksum_invalid() {
+        let data = [0x28, 0x00, 0x1A, 0x00, 0xFF];
+        assert!(!validate_checksum(&data));
+    }
+
+    #[test]
+    fn validate_checksum_wraps() {
+        let data = [0xFF, 0x01, 0x00, 0x00, 0x00];
+        assert!(validate_checksum(&data));
+    }
+
+    #[test]
+    fn parse_humidity_integer_only() {
+        let data = [0x41, 0x00, 0x00, 0x00, 0x41];
+        let h = parse_humidity(&data);
+        assert!((h - 65.0).abs() < 0.01);
+    }
+
+    #[test]
+    fn parse_humidity_with_fraction() {
+        let data = [0x41, 0x03, 0x00, 0x00, 0x44];
+        let h = parse_humidity(&data);
+        assert!((h - 65.3).abs() < 0.01);
+    }
+
+    #[test]
+    fn parse_temperature_integer_only() {
+        let data = [0x00, 0x00, 0x19, 0x00, 0x19];
+        let t = parse_temperature(&data);
+        assert!((t - 25.0).abs() < 0.01);
+    }
+
+    #[test]
+    fn parse_temperature_with_fraction() {
+        let data = [0x00, 0x00, 0x19, 0x05, 0x1E];
+        let t = parse_temperature(&data);
+        assert!((t - 25.5).abs() < 0.01);
+    }
+
+    #[test]
+    fn format_reading_typical() {
+        let mut buf = [0u8; 48];
+        let n = format_reading(&mut buf, 65.0, 25.0);
+        assert_eq!(&buf[..n], b"Humidity: 65.0%  Temperature: 25.0 C");
+    }
+
+    #[test]
+    fn format_reading_with_fractions() {
+        let mut buf = [0u8; 48];
+        let n = format_reading(&mut buf, 65.3, 25.5);
+        assert_eq!(&buf[..n], b"Humidity: 65.3%  Temperature: 25.5 C");
+    }
+
+    #[test]
+    fn format_error_gpio4() {
+        let mut buf = [0u8; 48];
+        let n = format_error(&mut buf, 4);
+        assert_eq!(&buf[..n], b"DHT11 read failed - check wiring on GPIO 4");
+    }
+
+    #[test]
+    fn format_error_gpio15() {
+        let mut buf = [0u8; 48];
+        let n = format_error(&mut buf, 15);
+        assert_eq!(&buf[..n], b"DHT11 read failed - check wiring on GPIO 15");
+    }
+
+    #[test]
+    fn format_u8_single_digit() {
+        let mut buf = [0u8; 4];
+        let n = format_u8(&mut buf, 4);
+        assert_eq!(&buf[..n], b"4");
+    }
+
+    #[test]
+    fn format_u8_two_digits() {
+        let mut buf = [0u8; 4];
+        let n = format_u8(&mut buf, 15);
+        assert_eq!(&buf[..n], b"15");
+    }
+
+    #[test]
+    fn format_u8_three_digits() {
+        let mut buf = [0u8; 4];
+        let n = format_u8(&mut buf, 255);
+        assert_eq!(&buf[..n], b"255");
+    }
+}

drivers/0x09_dht11_rust/src/lib.rs

@@ -0,0 +1,9 @@
+//! @file lib.rs
+//! @brief Library root for the DHT11 driver crate
+//! @author Kevin Thomas
+//! @date 2025
+
+#![no_std]
+
+// DHT11 driver module
+pub mod dht11;

drivers/0x09_dht11_rust/src/main.rs

@@ -0,0 +1,120 @@
+//! @file main.rs
+//! @brief DHT11 temperature and humidity sensor demonstration
+//! @author Kevin Thomas
+//! @date 2025
+//!
+//! MIT License
+//!
+//! Copyright (c) 2025 Kevin Thomas
+//!
+//! Permission is hereby granted, free of charge, to any person obtaining a copy
+//! of this software and associated documentation files (the "Software"), to deal
+//! in the Software without restriction, including without limitation the rights
+//! to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//! copies of the Software, and to permit persons to whom the Software is
+//! furnished to do so, subject to the following conditions:
+//!
+//! The above copyright notice and this permission notice shall be included in
+//! all copies or substantial portions of the Software.
+//!
+//! THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//! IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//! FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//! AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//! LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//! OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//! SOFTWARE.
+//!
+//! -----------------------------------------------------------------------------
+//!
+//! Demonstrates how to read temperature and humidity from a DHT11
+//! sensor using the dht11.rs driver. The sensor is polled every 2
+//! seconds (the minimum safe interval for the DHT11) and the results
+//! are printed over UART. A failed read is reported so wiring issues
+//! are visible.
+//!
+//! Wiring:
+//!   GPIO4 -> DHT11 DATA pin  (10 kohm pull-up to 3.3 V recommended)
+//!   3.3V  -> DHT11 VCC
+//!   GND   -> DHT11 GND
+
+#![no_std]
+#![no_main]
+
+// Board-level helpers: constants, type aliases, and init functions
+mod board;
+// DHT11 driver module — suppress warnings for unused public API functions
+#[allow(dead_code)]
+mod dht11;
+
+// Debugging output over RTT
+use defmt_rtt as _;
+// Panic handler for RISC-V targets
+#[cfg(target_arch = "riscv32")]
+use panic_halt as _;
+// Panic handler for ARM targets
+#[cfg(target_arch = "arm")]
+use panic_probe as _;
+
+// HAL entry-point macro
+use hal::entry;
+
+// Alias our HAL crate
+#[cfg(rp2350)]
+use rp235x_hal as hal;
+#[cfg(rp2040)]
+use rp2040_hal as hal;
+
+// Second-stage boot loader for RP2040
+#[unsafe(link_section = ".boot2")]
+#[used]
+#[cfg(rp2040)]
+pub static BOOT2: [u8; 256] = rp2040_boot2::BOOT_LOADER_W25Q080;
+
+// Boot metadata for the RP2350 Boot ROM
+#[unsafe(link_section = ".start_block")]
+#[used]
+#[cfg(rp2350)]
+pub static IMAGE_DEF: hal::block::ImageDef = hal::block::ImageDef::secure_exe();
+
+/// Application entry point for the DHT11 sensor demo.
+///
+/// Initializes the DHT11 on GPIO4 and continuously reads temperature
+/// and humidity, printing results over UART every 2 seconds.
+///
+/// # Returns
+///
+/// Does not return.
+#[entry]
+fn main() -> ! {
+    let mut pac = hal::pac::Peripherals::take().unwrap();
+    let clocks = board::init_clocks(
+        pac.XOSC, pac.CLOCKS, pac.PLL_SYS, pac.PLL_USB, &mut pac.RESETS,
+        &mut hal::Watchdog::new(pac.WATCHDOG),
+    );
+    let pins = board::init_pins(pac.IO_BANK0, pac.PADS_BANK0, pac.SIO, &mut pac.RESETS);
+    let uart = board::init_uart(pac.UART0, pins.gpio0, pins.gpio1, &mut pac.RESETS, &clocks);
+    let mut delay = board::init_delay(&clocks);
+    #[cfg(rp2350)]
+    let timer = hal::Timer::new_timer0(pac.TIMER0, &mut pac.RESETS, &clocks);
+    #[cfg(rp2040)]
+    let timer = hal::Timer::new(pac.TIMER, &mut pac.RESETS);
+    let _dht_pin = pins.gpio4.into_pull_up_input();
+    uart.write_full_blocking(b"DHT11 driver initialized on GPIO 4\r\n");
+    loop {
+        board::poll_sensor(&uart, &timer, &mut delay);
+    }
+}
+
+// Picotool binary info metadata
+#[unsafe(link_section = ".bi_entries")]
+#[used]
+pub static PICOTOOL_ENTRIES: [hal::binary_info::EntryAddr; 5] = [
+    hal::binary_info::rp_cargo_bin_name!(),
+    hal::binary_info::rp_cargo_version!(),
+    hal::binary_info::rp_program_description!(c"DHT11 Sensor Demo"),
+    hal::binary_info::rp_cargo_homepage_url!(),
+    hal::binary_info::rp_program_build_attribute!(),
+];
+
+// End of file