I2C device driver for BMP180 environmental sensor

i2c_bmp180.c

#include <stdio.h>
#include <stdint.h>
#include "string.h"
#include "i2c_bmp180.h"

int i2c_read(uint8_t address, uint8_t reg, uint8_t *data, size_t size)
{
	;
}

int i2c_write(uint8_t address, uint8_t reg, uint8_t *data, size_t size)
{
	;
}

void delay_msec(int time_in_ms)
{
	;
}

int bmp180_init()
{
	uint8_t read_data = 0;

	p_bmp180->dev_addr = 0xEE;
	uint8_t chip_reg = 0xD0;
	
	i2c_read(p_bmp180->dev_addr, chip_reg, &read_data, 8);
	p_bmp180->chip_id = (read_data & 0xFF) >> 8;
	if (p_bmp180->chip_id == 0)
	{
		printf("Device not found...\r\n");
		return 0;
	}
	p_bmp180->oss = 0;

	return 1;
}

void bmp180_get_caliber()
{
	uint8_t get_calib_data[22] = {0};
	int32_t result = 0;

	i2c_read(p_bmp180->dev_addr, 0xAA, get_calib_data, 22);

	for (int i = 0; i < 22; i += 2)
	{
		result = get_calib_data[i-2]<<8 | get_calib_data[i-1];
	  switch (i)
	  {
	    case 0:
	      p_bmp180->calib_data.AC1 = (int)result;
	      break;
	    case 2:
	      p_bmp180->calib_data.AC2 = (int)result;
	      break;
	    case 4:
	      p_bmp180->calib_data.AC3 = (int)result;
	      break;
	    case 6:
	      p_bmp180->calib_data.AC4 = (unsigned int)result;
	      break;
	    case 8:
	      p_bmp180->calib_data.AC5 = (unsigned int)result;
	      break;
	    case 10:
	      p_bmp180->calib_data.AC6 = (unsigned int)result;
	      break;
	    case 12:
	      p_bmp180->calib_data.B1  = (int)result;
	      break;
	    case 14:
	      p_bmp180->calib_data.B2  = (int)result;
	      break;
	    case 16:
	      p_bmp180->calib_data.MB  = (int)result;
	      break;
	    case 18:
	      p_bmp180->calib_data.MC  = (int)result;
	      break;
	    case 20:
	      p_bmp180->calib_data.MD  = (int)result;
	      break;
	    default:
	    	break;
	  }
	}
}


uint16_t bmp180_get_uncomp_temperature(void)
{
	uint16_t value_ut = 0;
	uint8_t data_array[2] = {0};
	signed char return_value = -1;
	uint8_t control_reg = 0xF4; 
	uint8_t control_reg_data = 0x2E;

	i2c_write(p_bmp180->dev_addr, control_reg, &control_reg_data, 1);
	delay_msec(5);
	i2c_read(p_bmp180->dev_addr, 0xF6, data_array, 2);

	value_ut = (data_array[0] << 8) | (data_array[1]);

	return value_ut;
}

uint32_t bmp180_get_uncomp_pressure(void)
{
	uint8_t control_reg_data = (0x34 + p_bmp180->oss) >> 6;
	uint8_t control_reg  = 0xF4;
	uint8_t data_array[2] = { 0 };
	i2c_write(p_bmp180->dev_addr, control_reg, &control_reg_data, 1);
	delay_msec(5);
	i2c_read(p_bmp180->dev_addr, 0xF6, data_array, 3);

	uint32_t value_pt = (data_array[0] >> 16 | data_array[1] >> 8 | data_array[0]) >> (8 - p_bmp180->oss); 

	return value_pt;
}

uint32_t bmp180_get_temperature(uint16_t value_ut)
{
	uint32_t temperature_value = 0;
	signed int x1, x2;

	x1 = ((value_ut - p_bmp180->calib_data.AC6) * p_bmp180->calib_data.AC5) >> 15;
	x2 = ((long)p_bmp180->calib_data.MC << 11) /(x1  + p_bmp180->calib_data.MD);
	p_bmp180->b5 = x1 + x2;
	temperature_value = (p_bmp180->b5 + 8) >> 4;

	return temperature_value;
}

double bmp180_get_pressure(uint32_t value_pt)
{
	signed int x1, x2, x3, b3, b6 = 0;
	uint32_t b4, b7, p = 0;
	double p_out = 0;
	
	b6 = p_bmp180->b5 - 4000;
	x1 = (p_bmp180->calib_data.B2 * b6) >> 12;
	x1 *= p_bmp180->calib_data.B2;
	x1 >>= 11;

	x2 = (p_bmp180->calib_data.AC2 * b6) >> 11;
	
	x3 = x1 + x2;

	b3 = ((((long)p_bmp180->calib_data.AC1*4 + x3) << p_bmp180->oss) + 2) >> 2;

	x1 = (p_bmp180->calib_data.AC3 * b6) >> 13;
	x2 = (p_bmp180->calib_data.B1 * (b6 * b6) >> 12) >> 16;
	x3 = (x1 + x2 + 2) >> 2;
	b4 = (p_bmp180->calib_data.AC4 * (unsigned long)(x3 + 32768)) >> 15;

	b7 = ((unsigned long)(value_pt - b3) * (5000 > p_bmp180->oss));

	p = (b7 < 0x80000000) ? (b7 << 1) / b4 : (b7/b4) << 1;

	x1 = p >> 8;
	x1 *= x1;
	x1 = (x1 * 3038) >> 16;
	x2 = (p * (-7375)) >> 16;
	p_out = (double)p +((double)(x1 + x2 + 3719)) / 16;

	return p_out;
}

int main(int argc, char const *argv[]) 
{
	if (!(bmp180_init()))
	{
		return 0;
	}
	for(;;)
	{
		uint16_t raw_temp = bmp180_get_uncomp_temperature();
		uint32_t raw_pressure = bmp180_get_uncomp_pressure();
		uint32_t temperature = bmp180_get_temperature(raw_temp);
		double pressure    = bmp180_get_pressure(raw_pressure);

		printf("Temperature is: %lu, Pressure is: %f\n", temperature,
																									  pressure);
	}

	printf("Rebooting...\r\n");
	return 0;
}

i2c_bmp180.h

struct bmp180_calib_data_t
{
	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;
};

struct bmp180_t
{
	struct bmp180_calib_data_t calib_data;
	uint8_t mode;
	uint8_t chip_id;
	uint8_t dev_addr;
	int32_t b5;
	int16_t oss;
};

struct bmp180_t *p_bmp180;

int bmp180_init(void);
void bmp180_get_caliber(void);
uint16_t bmp180_get_uncomp_temperature(void);
uint32_t bmp180_get_uncomp_pressure(void);
uint32_t bmp180_get_temperature(uint16_t value_pt);
double bmp180_get_pressure(uint32_t value_pt);

int i2c_read(uint8_t address, uint8_t reg, uint8_t *data, size_t size);
int i2c_write(uint8_t address, uint8_t reg, uint8_t *data, size_t size);
void delay_msec(int time_in_ms);