qtalker---/firmware/esp32p4-sensor-node/main/bmp280.c

// Bosch BMP280 driver — see bmp280.h for wiring and honesty notes.
//
// UNVERIFIED AGAINST REAL HARDWARE: this has been written against the public
// BMP280 datasheet (Bosch Sensortec, document rev 1.23) and ESP-IDF's
// documented `driver/i2c_master.h` API surface, and reasoned about carefully,
// but never compiled with a real ESP-IDF toolchain nor run against a real
// sensor. Register addresses and the compensation formula below are
// transcribed as directly as possible from the datasheet's section 3.11.1
// (register map) and 3.11.3 (double-precision compensation formula
// reference implementation) to minimize transcription risk, but a real
// bring-up should sanity-check first readings against a known-good
// reference (e.g. compare to a household thermometer/barometer).

#include <string.h>
#include <stdbool.h>
#include <math.h>
#include "bmp280.h"
#include "driver/i2c_master.h"
#include "esp_log.h"
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"

static const char *TAG = "bmp280";

// --- Register map (BMP280 datasheet section 3.11.1) ------------------------
#define REG_CHIP_ID       0xD0
#define REG_RESET         0xE0
#define REG_STATUS        0xF3
#define REG_CTRL_MEAS     0xF4
#define REG_CONFIG        0xF5
#define REG_PRESS_MSB     0xF7 // press(3) + temp(3) = 6 bytes, burst-read from here
#define REG_CALIB00       0x88 // dig_T1..dig_P9, 24 bytes: 0x88-0x9F

#define CHIP_ID_EXPECTED  0x58 // BMP280 (vs. BME280's 0x60 — a chip-ID
                                // mismatch here likely means a BME280 is
                                // wired instead; we proceed anyway since the
                                // temp/pressure register map and compensation
                                // math is identical between the two parts)

#define RESET_MAGIC       0xB6

#define STATUS_MEASURING_BIT 0x08

typedef struct {
    uint16_t dig_T1;
    int16_t  dig_T2;
    int16_t  dig_T3;
    uint16_t dig_P1;
    int16_t  dig_P2;
    int16_t  dig_P3;
    int16_t  dig_P4;
    int16_t  dig_P5;
    int16_t  dig_P6;
    int16_t  dig_P7;
    int16_t  dig_P8;
    int16_t  dig_P9;
} bmp280_calib_t;

static i2c_master_bus_handle_t s_bus = NULL;
static i2c_master_dev_handle_t s_dev = NULL;
static bmp280_calib_t s_calib;
static bool s_ready = false;

static esp_err_t write_reg(uint8_t reg, uint8_t val) {
    uint8_t buf[2] = { reg, val };
    return i2c_master_transmit(s_dev, buf, sizeof(buf), 1000 /* ms */);
}

static esp_err_t read_regs(uint8_t reg, uint8_t *out, size_t len) {
    return i2c_master_transmit_receive(s_dev, &reg, 1, out, len, 1000 /* ms */);
}

static int16_t s16(uint8_t lsb, uint8_t msb) {
    return (int16_t)((uint16_t)msb << 8 | lsb);
}
static uint16_t u16(uint8_t lsb, uint8_t msb) {
    return (uint16_t)((uint16_t)msb << 8 | lsb);
}

static esp_err_t read_calibration(void) {
    uint8_t buf[24]; // 0x88..0x9F

    esp_err_t err = read_regs(REG_CALIB00, buf, sizeof(buf));
    if (err != ESP_OK) return err;

    s_calib.dig_T1 = u16(buf[0], buf[1]);
    s_calib.dig_T2 = s16(buf[2], buf[3]);
    s_calib.dig_T3 = s16(buf[4], buf[5]);
    s_calib.dig_P1 = u16(buf[6], buf[7]);
    s_calib.dig_P2 = s16(buf[8], buf[9]);
    s_calib.dig_P3 = s16(buf[10], buf[11]);
    s_calib.dig_P4 = s16(buf[12], buf[13]);
    s_calib.dig_P5 = s16(buf[14], buf[15]);
    s_calib.dig_P6 = s16(buf[16], buf[17]);
    s_calib.dig_P7 = s16(buf[18], buf[19]);
    s_calib.dig_P8 = s16(buf[20], buf[21]);
    s_calib.dig_P9 = s16(buf[22], buf[23]);

    return ESP_OK;
}

esp_err_t bmp280_init(void) {
    i2c_master_bus_config_t bus_cfg = {
        .i2c_port = BMP280_I2C_PORT,
        .sda_io_num = BMP280_I2C_SDA_GPIO,
        .scl_io_num = BMP280_I2C_SCL_GPIO,
        .clk_source = I2C_CLK_SRC_DEFAULT,
        .glitch_ignore_cnt = 7,
        .flags.enable_internal_pullup = true,
    };
    esp_err_t err = i2c_new_master_bus(&bus_cfg, &s_bus);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "i2c_new_master_bus failed: %s", esp_err_to_name(err));
        return err;
    }

    i2c_device_config_t dev_cfg = {
        .dev_addr_length = I2C_ADDR_BIT_LEN_7,
        .device_address = BMP280_I2C_ADDR,
        .scl_speed_hz = BMP280_I2C_CLK_HZ,
    };
    err = i2c_master_bus_add_device(s_bus, &dev_cfg, &s_dev);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "i2c_master_bus_add_device failed: %s", esp_err_to_name(err));
        return err;
    }

    uint8_t chip_id = 0;
    err = read_regs(REG_CHIP_ID, &chip_id, 1);
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "chip id read failed: %s", esp_err_to_name(err));
        return err;
    }
    if (chip_id != CHIP_ID_EXPECTED) {
        ESP_LOGW(TAG, "unexpected chip id 0x%02x (want 0x%02x) -- check wiring/address", chip_id, CHIP_ID_EXPECTED);
        // Don't hard-fail: temp+pressure register map/compensation is
        // identical on a BME280 too, so a mis-wired-but-present sensor of
        // either part can still usefully report both readings.
    }

    err = write_reg(REG_RESET, RESET_MAGIC);
    if (err != ESP_OK) return err;
    vTaskDelay(pdMS_TO_TICKS(10)); // datasheet: allow >= 2ms after reset

    err = read_calibration();
    if (err != ESP_OK) {
        ESP_LOGE(TAG, "calibration read failed: %s", esp_err_to_name(err));
        return err;
    }

    s_ready = true;
    ESP_LOGI(TAG, "BMP280 init ok (chip id 0x%02x)", chip_id);
    return ESP_OK;
}

// Bosch datasheet 3.11.3 double-precision reference compensation formulas,
// transcribed near-verbatim (variable names kept close to the original so
// it's checkable against the datasheet PDF side-by-side).

static double compensate_temperature(int32_t adc_T, double *out_t_fine) {
    double var1 = (((double)adc_T) / 16384.0 - ((double)s_calib.dig_T1) / 1024.0) * ((double)s_calib.dig_T2);
    double var2 = ((((double)adc_T) / 131072.0 - ((double)s_calib.dig_T1) / 8192.0) *
                   (((double)adc_T) / 131072.0 - ((double)s_calib.dig_T1) / 8192.0)) * ((double)s_calib.dig_T3);
    *out_t_fine = var1 + var2;
    return (var1 + var2) / 5120.0; // degrees C
}

static double compensate_pressure(int32_t adc_P, double t_fine) {
    double var1 = (t_fine / 2.0) - 64000.0;
    double var2 = var1 * var1 * ((double)s_calib.dig_P6) / 32768.0;
    var2 = var2 + var1 * ((double)s_calib.dig_P5) * 2.0;
    var2 = (var2 / 4.0) + (((double)s_calib.dig_P4) * 65536.0);
    var1 = (((double)s_calib.dig_P3) * var1 * var1 / 524288.0 + ((double)s_calib.dig_P2) * var1) / 524288.0;
    var1 = (1.0 + var1 / 32768.0) * ((double)s_calib.dig_P1);
    if (var1 == 0.0) {
        return 0.0; // avoid divide-by-zero per datasheet's own guard
    }
    double p = 1048576.0 - (double)adc_P;
    p = (p - (var2 / 4096.0)) * 6250.0 / var1;
    var1 = ((double)s_calib.dig_P9) * p * p / 2147483648.0;
    var2 = p * ((double)s_calib.dig_P8) / 32768.0;
    p = p + (var1 + var2 + ((double)s_calib.dig_P7)) / 16.0;
    return p; // Pa
}

esp_err_t bmp280_read(sensor_reading_t *out, size_t max_out, size_t *out_count) {
    *out_count = 0;
    if (!s_ready) {
        return ESP_ERR_INVALID_STATE;
    }
    if (max_out < 2) {
        return ESP_ERR_NO_MEM;
    }

    // Forced mode: osrs_t=1 (001), osrs_p=1 (001), mode=forced (01).
    // ctrl_meas = 0b001_001_01 = 0x25
    esp_err_t err = write_reg(REG_CTRL_MEAS, 0x25);
    if (err != ESP_OK) return err;

    // Poll status until the "measuring" bit clears, with a hard cap so a
    // wedged bus/sensor can't hang the telemetry task forever.
    for (int attempt = 0; attempt < 20; attempt++) {
        uint8_t status = 0;
        err = read_regs(REG_STATUS, &status, 1);
        if (err != ESP_OK) return err;
        if ((status & STATUS_MEASURING_BIT) == 0) {
            break;
        }
        vTaskDelay(pdMS_TO_TICKS(5));
        if (attempt == 19) {
            ESP_LOGW(TAG, "measurement did not complete in time");
            return ESP_ERR_TIMEOUT;
        }
    }

    uint8_t raw[6];
    err = read_regs(REG_PRESS_MSB, raw, sizeof(raw));
    if (err != ESP_OK) return err;

    int32_t adc_P = ((int32_t)raw[0] << 12) | ((int32_t)raw[1] << 4) | (raw[2] >> 4);
    int32_t adc_T = ((int32_t)raw[3] << 12) | ((int32_t)raw[4] << 4) | (raw[5] >> 4);

    double t_fine = 0.0;
    double temp_c = compensate_temperature(adc_T, &t_fine);
    double press_pa = compensate_pressure(adc_P, t_fine);

    size_t n = 0;
    memset(&out[n], 0, sizeof(out[n]));
    strncpy(out[n].sensor_type, "temperature", SENSOR_READING_TYPE_MAXLEN - 1);
    out[n].value = temp_c;
    strncpy(out[n].unit, "c", SENSOR_READING_UNIT_MAXLEN - 1);
    out[n].metadata = NULL;
    n++;

    memset(&out[n], 0, sizeof(out[n]));
    strncpy(out[n].sensor_type, "pressure", SENSOR_READING_TYPE_MAXLEN - 1);
    out[n].value = press_pa / 100.0; // Pa -> hPa
    strncpy(out[n].unit, "hpa", SENSOR_READING_UNIT_MAXLEN - 1);
    out[n].metadata = NULL;
    n++;

    *out_count = n;
    return ESP_OK;
}