# Read temperature via I2C from DS1621
# Customize the code according your device name
# Copyleft 2013 Chaosdorf

#include <stdio.h>
#include <stdint.h>
#include <fcntl.h>
#include <stdlib.h>
#include <linux/i2c-dev.h>

int main(void)
{
int file;
char filename[20];
int addr = 0x48; /* The I2C address */
int32_t temperature;
int32_t temp_int;
int32_t temp_counter;
int32_t temp_slope;

// Open a file giving access to i2c interface 1

sprintf(filename,"/dev/i2c-1");
if ((file = open(filename,O_RDWR)) < 0) {
printf("No access\n");
exit(1);
}

// Check that the chip is there

if (ioctl(file,I2C_SLAVE,addr) < 0) {
printf("No chip detected\n");
exit(1);
}

// Set up continuous measurement

if (i2c_smbus_write_byte_data(file, 0xac, 0x00) < 0) {
printf("Set continuos mesurement failed\n");
exit(1);
}

// Start measurements

if (i2c_smbus_write_byte(file, 0xee) < 0) {
printf("Start measurements failed\n");
exit(1);
}

// read TEMP_INT

if ((temp_int = i2c_smbus_read_byte_data(file, 0xaa)) < 0) {
printf("Read temp_int failed\n");
exit(1);
}

// read TEMP_COUNTER

if ((temp_counter = i2c_smbus_read_byte_data(file, 0xa8)) < 0) {
printf("Read temp_counter failed\n");
exit(1);
}

// read TEMP_SLOPE

if ((temp_slope = i2c_smbus_read_byte_data(file, 0xa9)) < 0) {
printf("Read temp_scope failed\n");
exit(1);
}

// calculate temperaure


temperature = temp_int * 100 - 25 + ((temp_slope - temp_counter) * 100 / temp_slope);

printf("%d", (int32_t)temperature);
close(file);
exit(0);
}