bmp180.c

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <math.h>
#include <linux/i2c-dev.h>
#include <stdint.h>

int reg_write_byte(int handle, uint8_t devaddr, uint8_t regaddr,
		uint8_t content) {
	struct i2c_rdwr_ioctl_data iocall;    // structure pass to i2c driver
	struct i2c_msg message;
	uint8_t buffer[2];

	buffer[0] = regaddr;
	buffer[1] = content;

	iocall.nmsgs = 1;
	iocall.msgs = &message;
	message.addr = devaddr;
	message.flags = 0; //write
	message.buf = (char*) buffer;
	message.len = sizeof(buffer);
	if (ioctl(handle, I2C_RDWR, (unsigned long) &iocall) < 0) {
		printf("error during reg_write_byte()\n");
		return -1;
	}
	return 0;
}

int reg_read_byte(int handle, uint8_t devaddr, uint8_t regaddr,
		uint8_t* content) {
	struct i2c_rdwr_ioctl_data iocall;    // structure pass to i2c driver
	struct i2c_msg messages[2];

	iocall.nmsgs = 2;
	iocall.msgs = messages;

	messages[0].addr = devaddr;
	messages[0].flags = 0; //write
	messages[0].buf = (char*) &regaddr;
	messages[0].len = 1;

	messages[1].addr = devaddr;
	messages[1].flags = I2C_M_RD; //READ
	messages[1].buf = (char*) content;
	messages[1].len = 1;

	if (ioctl(handle, I2C_RDWR, (unsigned long) &iocall) < 0) {
		printf("error during reg_read_byte()\n");
		return -1;
	}
	return 0;
}

int reg_read_short(int handle, uint8_t devaddr, uint8_t regaddr,
		uint16_t* content) {
	struct i2c_rdwr_ioctl_data iocall;    // structure pass to i2c driver
	struct i2c_msg messages[2];
	uint8_t buffer[2];

	iocall.nmsgs = 2;
	iocall.msgs = messages;

	messages[0].addr = devaddr;
	messages[0].flags = 0; //write
	messages[0].buf = (char*) &regaddr;
	messages[0].len = 1;

	messages[1].addr = devaddr;
	messages[1].flags = I2C_M_RD; //READ
	messages[1].buf = (char*) buffer;
	messages[1].len = 2;

	if (ioctl(handle, I2C_RDWR, (unsigned long) &iocall) < 0) {
		printf("error during reg_read_short()\n");
		return -1;
	}

	*content = (uint16_t) (buffer[0] << 8) | buffer[1];
	return 0;
}

int reg_read_24(int handle, uint8_t devaddr, uint8_t regaddr, int32_t* content) {
	struct i2c_rdwr_ioctl_data iocall;    // structure pass to i2c driver
	struct i2c_msg messages[2];
	uint8_t buffer[3];

	iocall.nmsgs = 2;
	iocall.msgs = messages;

	messages[0].addr = devaddr;
	messages[0].flags = 0; //write
	messages[0].buf = (char*) &regaddr;
	messages[0].len = 1;

	messages[1].addr = devaddr;
	messages[1].flags = I2C_M_RD; //READ
	messages[1].buf = (char*) buffer;
	messages[1].len = 3;

	if (ioctl(handle, I2C_RDWR, (unsigned long) &iocall) < 0) {
		printf("error during reg_read_short()\n");
		return -1;
	}

	*content = (buffer[0] << 16) | (buffer[1] << 8) | buffer[2];
	return 0;
}

typedef struct {
	int16_t AC1; // =   408;
	int16_t AC2; // =   -72;
	int16_t AC3; // =-14383;
	uint16_t AC4; //=32741;
	uint16_t AC5; //=32757;
	uint16_t AC6; //=23153;
	int16_t B1; //=   6190;
	int16_t B2; //=      4;
	int16_t MB; //= -32768;
	int16_t MC; //=  -8711;
	int16_t MD; //=   2868;
} bmp180_calibration;

#define BMP180_I2C_ADDR (0x77)

int bmp180_read_cal(int fd, bmp180_calibration* cal) {
	int res = 0;
	res |= reg_read_short(fd, BMP180_I2C_ADDR, 0xaa, (uint16_t*) &cal->AC1);
	res |= reg_read_short(fd, BMP180_I2C_ADDR, 0xac, (uint16_t*) &cal->AC2);
	res |= reg_read_short(fd, BMP180_I2C_ADDR, 0xae, (uint16_t*) &cal->AC3);
	res |= reg_read_short(fd, BMP180_I2C_ADDR, 0xb0, (uint16_t*) &cal->AC4);
	res |= reg_read_short(fd, BMP180_I2C_ADDR, 0xb2, (uint16_t*) &cal->AC5);
	res |= reg_read_short(fd, BMP180_I2C_ADDR, 0xb4, (uint16_t*) &cal->AC6);

	res |= reg_read_short(fd, BMP180_I2C_ADDR, 0xb6, (uint16_t*) &cal->B1);
	res |= reg_read_short(fd, BMP180_I2C_ADDR, 0xb8, (uint16_t*) &cal->B2);

	res |= reg_read_short(fd, BMP180_I2C_ADDR, 0xba, (uint16_t*) &cal->MB);
	res |= reg_read_short(fd, BMP180_I2C_ADDR, 0xbc, (uint16_t*) &cal->MC);
	res |= reg_read_short(fd, BMP180_I2C_ADDR, 0xbe, (uint16_t*) &cal->MD);

	return res;
}

int main(void) {
	const char* device = "/dev/i2c-1";
	int fd = open(device, O_RDWR);
	if (fd < 0) {
		perror("Failed to open device");
		return -1;
	}

	ioctl(fd, I2C_TIMEOUT, 3); // i2c timeout, 1 for 10ms ; if too small, i2c may lose response
	ioctl(fd, I2C_RETRIES, 3);    // i2c retry limit

	bmp180_calibration cal;

	if (0 == bmp180_read_cal(fd, &cal)) {
//        printf("Calibration read\n",cal.AC1);
	} else {
		printf("Error reading calibration\n");
		return -1;
	}

	int32_t X1;
	int32_t X2;
	int32_t X3;

	int32_t B3;
	int32_t B4;
	int32_t B5;
	int32_t B6;
	int32_t B7;
	int32_t T;
	int32_t p;
	int16_t oss = 3;

	reg_write_byte(fd, BMP180_I2C_ADDR, 0xf4, 0x2e); //Start Temperature Measurement
	usleep(4500); //Wait for Temperature measurement
	uint16_t temp16;
	reg_read_short(fd, BMP180_I2C_ADDR, 0xf6, &temp16);
	int32_t UT = temp16;

	reg_write_byte(fd, BMP180_I2C_ADDR, 0xf4, 0x34 + (oss << 6)); //Start Pressure Measurement
	usleep(25500); //Wait for precise pressure measurement
	int32_t UP;
	reg_read_24(fd, BMP180_I2C_ADDR, 0xf6, &UP);
	UP = UP >> (8 - oss);

	X1 = (UT - cal.AC6) * cal.AC5 / (1 << 15);
	X2 = cal.MC * (1 << 11) / (X1 + cal.MD);
	B5 = (X1 + X2);
	T = (B5 + 8) / (1 << 4);
//    printf("Temperature is %i.%i°C\n",T/10,T%10);

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

//    printf("Pressure is %i Pa\n",p);
	double p0;
        double pd;
	pd=(double)p;
	double alt = 125;
	p0 =  p / pow(1 - alt / 44330.0, 5.255);
//    printf("Assuming we are at %.1f m elevation the Pressure at sea level is %0.1f hPa\n",alt,p0/100);
	printf("%i.%i;", T / 10, T % 10);
	printf("%0.1f;", pd / 100);
	printf("%0.1f\n", p0 / 100);
	return (0);
}