ESP32/main/temp_humidity_monitor.c

#include "temp_humidity_monitor.h"

#include <stdint.h>

#include "driver/i2c_master.h"
#include "esp_check.h"
#include "esp_err.h"
#include "esp_log.h"
#include "freertos/FreeRTOS.h"
#include "freertos/portmacro.h"
#include "freertos/task.h"

static const char *TAG = "shtc3";

#define SHTC3_I2C_PORT I2C_NUM_0
#define SHTC3_I2C_SDA GPIO_NUM_13
#define SHTC3_I2C_SCL GPIO_NUM_14
#define SHTC3_I2C_ADDRESS 0x70
#define SHTC3_I2C_HZ 100000
#define SHTC3_WAKEUP_CMD 0x3517
#define SHTC3_SLEEP_CMD 0xB098
#define SHTC3_MEASURE_CMD 0x7866

static i2c_master_bus_handle_t s_i2c_bus;
static i2c_master_dev_handle_t s_shtc3_dev;
static portMUX_TYPE s_env_mux = portMUX_INITIALIZER_UNLOCKED;
static int s_latest_temperature_c10;
static int s_latest_humidity_percent;
static bool s_has_latest;

static uint8_t shtc3_crc(const uint8_t *data)
{
    uint8_t crc = 0xFF;

    for (int i = 0; i < 2; i++) {
        crc ^= data[i];
        for (int bit = 0; bit < 8; bit++) {
            if ((crc & 0x80) != 0) {
                crc = (uint8_t)((crc << 1) ^ 0x31);
            } else {
                crc <<= 1;
            }
        }
    }

    return crc;
}

static esp_err_t shtc3_send_command(uint16_t command)
{
    uint8_t data[2] = {
        (uint8_t)(command >> 8),
        (uint8_t)(command & 0xFF),
    };
    return i2c_master_transmit(s_shtc3_dev, data, sizeof(data), 1000);
}

static esp_err_t shtc3_read_once(int *temperature_c10, int *humidity_percent)
{
    uint8_t data[6] = { 0 };

    ESP_RETURN_ON_ERROR(shtc3_send_command(SHTC3_WAKEUP_CMD), TAG, "wake failed");
    vTaskDelay(pdMS_TO_TICKS(2));
    ESP_RETURN_ON_ERROR(shtc3_send_command(SHTC3_MEASURE_CMD), TAG, "measure failed");
    vTaskDelay(pdMS_TO_TICKS(15));
    ESP_RETURN_ON_ERROR(i2c_master_receive(s_shtc3_dev, data, sizeof(data), 1000), TAG, "read failed");
    (void)shtc3_send_command(SHTC3_SLEEP_CMD);

    if (shtc3_crc(&data[0]) != data[2] || shtc3_crc(&data[3]) != data[5]) {
        return ESP_ERR_INVALID_CRC;
    }

    uint16_t raw_temp = ((uint16_t)data[0] << 8) | data[1];
    uint16_t raw_humidity = ((uint16_t)data[3] << 8) | data[4];
    *temperature_c10 = -450 + (int)((1750L * raw_temp + 32767) / 65535);
    *humidity_percent = (int)((100L * raw_humidity + 32767) / 65535);
    if (*humidity_percent < 0) {
        *humidity_percent = 0;
    } else if (*humidity_percent > 100) {
        *humidity_percent = 100;
    }

    return ESP_OK;
}

static esp_err_t shtc3_init(void)
{
    i2c_master_bus_config_t bus_config = {
        .i2c_port = SHTC3_I2C_PORT,
        .sda_io_num = SHTC3_I2C_SDA,
        .scl_io_num = SHTC3_I2C_SCL,
        .clk_source = I2C_CLK_SRC_DEFAULT,
        .glitch_ignore_cnt = 7,
        .flags.enable_internal_pullup = true,
    };
    ESP_RETURN_ON_ERROR(i2c_new_master_bus(&bus_config, &s_i2c_bus), TAG, "i2c bus init failed");

    i2c_device_config_t device_config = {
        .dev_addr_length = I2C_ADDR_BIT_LEN_7,
        .device_address = SHTC3_I2C_ADDRESS,
        .scl_speed_hz = SHTC3_I2C_HZ,
    };
    ESP_RETURN_ON_ERROR(i2c_master_bus_add_device(s_i2c_bus, &device_config, &s_shtc3_dev),
                        TAG,
                        "shtc3 device add failed");
    return ESP_OK;
}

static void temp_humidity_task(void *arg)
{
    (void)arg;

    while (1) {
        int temperature_c10 = 0;
        int humidity_percent = 0;
        esp_err_t ret = shtc3_read_once(&temperature_c10, &humidity_percent);
        if (ret == ESP_OK) {
            portENTER_CRITICAL(&s_env_mux);
            s_latest_temperature_c10 = temperature_c10;
            s_latest_humidity_percent = humidity_percent;
            s_has_latest = true;
            portEXIT_CRITICAL(&s_env_mux);
        } else {
            ESP_LOGW(TAG, "read disabled this round: %s", esp_err_to_name(ret));
        }

        vTaskDelay(pdMS_TO_TICKS(10000));
    }
}

void temp_humidity_monitor_start(void)
{
    esp_err_t ret = shtc3_init();
    if (ret != ESP_OK) {
        ESP_LOGW(TAG, "temperature/humidity monitor disabled: %s", esp_err_to_name(ret));
        return;
    }

    xTaskCreate(temp_humidity_task, "shtc3", 4096, NULL, 2, NULL);
}

bool temp_humidity_monitor_take_latest(int *temperature_c10, int *humidity_percent)
{
    if (temperature_c10 == NULL || humidity_percent == NULL) {
        return false;
    }

    bool has_latest = false;
    portENTER_CRITICAL(&s_env_mux);
    if (s_has_latest) {
        *temperature_c10 = s_latest_temperature_c10;
        *humidity_percent = s_latest_humidity_percent;
        s_has_latest = false;
        has_latest = true;
    }
    portEXIT_CRITICAL(&s_env_mux);

    return has_latest;
}