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0x001a_operators/dht11.c

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+/**
+ * @file dht11.c
+ * @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.
+ */
+
+#include "dht11.h"
+#include "hardware/gpio.h"
+#include "pico/time.h"
+
+/** @brief GPIO pin connected to the DHT11 sensor */
+static uint dht_pin;
+
+/**
+ * @brief 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.
+ */
+static void send_start_signal(void) {
+    gpio_set_dir(dht_pin, GPIO_OUT);
+    gpio_put(dht_pin, 0);
+    sleep_ms(18);
+    gpio_put(dht_pin, 1);
+    sleep_us(40);
+    gpio_set_dir(dht_pin, GPIO_IN);
+}
+
+/**
+ * @brief Wait for the pin to leave a given logic level
+ *
+ * Spins until the pin no longer reads the specified level, returning
+ * false if a timeout of 10 000 iterations is exceeded.
+ *
+ * @param level Logic level to wait through (0 or 1)
+ * @return bool true once the level changed, false on timeout
+ */
+static bool wait_for_level(int level) {
+    uint32_t timeout = 10000;
+    while (gpio_get(dht_pin) == level)
+        if (--timeout == 0) return false;
+    return true;
+}
+
+/**
+ * @brief 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.
+ *
+ * @return bool true if the full response was received, false on timeout
+ */
+static bool wait_response(void) {
+    if (!wait_for_level(1)) return false;
+    if (!wait_for_level(0)) return false;
+    if (!wait_for_level(1)) return false;
+    return true;
+}
+
+/**
+ * @brief Read a single bit from the DHT11 data stream
+ *
+ * Waits for the low-period to end, measures the high-period duration,
+ * and shifts the result into the appropriate byte of the data array.
+ *
+ * @param data 5-byte array accumulating the received bits
+ * @param i    Bit index (0-39)
+ * @return bool true on success, false on timeout
+ */
+static bool read_bit(uint8_t *data, int i) {
+    if (!wait_for_level(0)) return false;
+    uint32_t start = time_us_32();
+    if (!wait_for_level(1)) return false;
+    uint32_t duration = time_us_32() - start;
+    data[i / 8] <<= 1;
+    if (duration > 40) data[i / 8] |= 1;
+    return true;
+}
+
+/**
+ * @brief Read all 40 data bits from the DHT11
+ *
+ * @param data 5-byte array filled with the received data
+ * @return bool true if all 40 bits were read, false on timeout
+ */
+static bool read_40_bits(uint8_t *data) {
+    for (int i = 0; i < 40; i++)
+        if (!read_bit(data, i)) return false;
+    return true;
+}
+
+/**
+ * @brief Verify the DHT11 checksum byte
+ *
+ * @param data 5-byte received data (bytes 0-3 plus checksum in byte 4)
+ * @return bool true if the checksum matches, false otherwise
+ */
+static bool validate_checksum(const uint8_t *data) {
+    return data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF);
+}
+
+void dht11_init(uint8_t pin) {
+    dht_pin = pin;
+    gpio_init(pin);
+    gpio_pull_up(pin);
+}
+
+bool dht11_read(float *humidity, float *temperature) {
+    uint8_t data[5] = {0};
+    send_start_signal();
+    if (!wait_response()) return false;
+    if (!read_40_bits(data)) return false;
+    if (!validate_checksum(data)) return false;
+    *humidity = data[0] + data[1] * 0.1f;
+    *temperature = data[2] + data[3] * 0.1f;
+    return true;
+}