pico_i2c_bmp180.c

#include <stdio.h>
#include "pico/stdlib.h"
#include "hardware/i2c.h"

struct calibration_data {
	int16_t	AC1;
	int16_t	AC2;
	int16_t	AC3;
	uint16_t AC4;
	uint16_t AC5;
	uint16_t AC6;
	int16_t	B1;
	int16_t	B2;
	int16_t	MB;
	int16_t	MC;
	int16_t	MD;

	int32_t	B3;
	uint32_t B4;
	int32_t	B5;
	int32_t	B6;
	uint32_t B7;
};

void get_calibration_data(struct calibration_data *data) {
    uint8_t buf[22];

    buf[0] = 0xAA;
    i2c_write_blocking(i2c_default, 0x77, buf, 1, true);
    i2c_read_blocking(i2c_default, 0x77, buf, 22, false);

    data->AC1 = (buf[0] << 8) | buf[1];
    data->AC2 = (buf[2] << 8) | buf[3];
    data->AC3 = (buf[4] << 8) | buf[5];
    data->AC4 = (buf[6] << 8) | buf[7];
    data->AC5 = (buf[8] << 8) | buf[9];
    data->AC6 = (buf[10] << 8) | buf[11];
    data->B1  = (buf[12] << 8) | buf[13];
    data->B2  = (buf[14] << 8) | buf[15];
    data->MB  = (buf[16] << 8) | buf[17];
    data->MC  = (buf[18] << 8) | buf[19];
    data->MD  = (buf[20] << 8) | buf[21];
}

int32_t read_uncompensated_temperature_value() {
    uint8_t buf[2];

    buf[0] = 0xF4;
    buf[1] = 0x2E;
    i2c_write_blocking(i2c_default, 0x77, buf, 2, false);
    sleep_ms(5);

    buf[0] = 0xF6;
    i2c_write_blocking(i2c_default, 0x77, buf, 1, true);
    i2c_read_blocking(i2c_default, 0x77, buf, 2, false);

    return (buf[0] << 8) | buf[1];
}

int32_t read_uncompensated_pressure_value() {
    uint8_t buf[3];
    int16_t oss = 0;

    buf[0] = 0xF4;
    buf[1] = 0x34 + (oss << 6);
    i2c_write_blocking(i2c_default, 0x77, buf, 2, false);
    sleep_ms(26);

    buf[0] = 0xF6;
    i2c_write_blocking(i2c_default, 0x77, buf, 1, true);
    i2c_read_blocking(i2c_default, 0x77, buf, 3, false);

    return (buf[0] << 16 | buf[1] << 8 | buf[2]) >> (8 - oss);
}

int32_t calculate_true_temperature(struct calibration_data *data, int32_t raw_temp) {
	int32_t X1 = ((raw_temp - data->AC6) * data->AC5) >> 15;
	int32_t X2 = (data->MC << 11) / (X1 + data->MD);
	data->B5 = X1 + X2;
	int32_t true_temp = (data->B5 + 8) >> 4;

	return true_temp;
}

int32_t calculate_true_pressure(struct calibration_data *data, int32_t raw_pres) {
	int16_t oss = 0;

	data->B6 = data->B5 - 4000;
	int32_t X1 = (data->B2 * ((data->B6 * data->B6) >> 12)) >> 11;
	int32_t X2 = (data->AC2 * data->B6) >> 11;
	int32_t X3 = X1 + X2;
	data->B3 = (((data->AC1 << 2 + X3) << oss) + 2) >> 2;
	X1 = (data->AC3 * data->B6) >> 13;
	X2 = (data->B1 * ((data->B6 * data->B6) >> 12)) >> 16;
	X3 = ((X1 + X2) + 2) >> 2;
	data->B4 = (data->AC4 * (uint32_t)(X3 + 32768)) >> 15;
	data->B7 = ((uint32_t)raw_pres - data->B3) * (50000 >> oss);
	int32_t p;
	if(data->B7 < 0x80000000) p = (data->B7 << 1) / data->B4;
	else p = (data->B7 / data->B4) << 1;
	X1 = (p >> 8) * (p >> 8);
	X1 = (X1 * 3038) >> 16;
	X2 = (-7357 * p) >> 16;
	int32_t true_pres = p + ((X1 + X2 + 3791) >> 4);

	return true_pres;
}

int main()
{
    stdio_init_all();
    sleep_ms(3000);

    i2c_init(i2c_default, 100 * 1000);
    gpio_set_function(PICO_DEFAULT_I2C_SDA_PIN, GPIO_FUNC_I2C);
    gpio_set_function(PICO_DEFAULT_I2C_SCL_PIN, GPIO_FUNC_I2C);
    gpio_pull_up(PICO_DEFAULT_I2C_SDA_PIN);
    gpio_pull_up(PICO_DEFAULT_I2C_SCL_PIN);

    struct calibration_data data;
    get_calibration_data(&data);

    int32_t raw_temp = read_uncompensated_temperature_value();
    int32_t raw_pres = read_uncompensated_pressure_value();
    printf("raw_temp: %d\n", raw_temp);
    printf("raw_pres: %d\n\n", raw_pres);

    int32_t true_temp = calculate_true_temperature(&data, raw_temp);
    int32_t true_pres = calculate_true_pressure(&data, raw_temp);
    printf("true_temp: %d\n", true_temp);
    printf("true_pres: %d\n", true_pres);

    return 0;
}

// stdio

// raw_temp: 27964
// raw_pres: 42984
// 
// true_temp: 232
// true_pres: 83113