#include <stdio.h>
#include <stdint.h>
#include <linux/i2c.h>
#include <linux/i2c-dev.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <string.h>
#define BMP180_I2C_ADDR                 (0xee)
#define BMP180_I2C_ADDR_R                 (BMP180_I2C_ADDR)
#define BMP180_I2C_ADDR_W                (BMP180_I2C_ADDR | 1)
#define BMP180_REG_ADDR_TEMPERATURE        (0x2E)
#define I2C_DEV_NAME                    "/dev/i2c-0"



static int set_i2c_register(int file,
                            unsigned char addr,
                            unsigned char reg,
                            unsigned char value) {

    unsigned char outbuf[2];
    struct i2c_rdwr_ioctl_data packets;
    struct i2c_msg messages[1];

    messages[0].addr  = addr;
    messages[0].flags = 0;
    messages[0].len   = sizeof(outbuf);
    messages[0].buf   = outbuf;

    /* The first byte indicates which register we'll write */
    outbuf[0] = reg;

    /* 
     * The second byte indicates the value to write.  Note that for many
     * devices, we can write multiple, sequential registers at once by
     * simply making outbuf bigger.
     */
    outbuf[1] = value;

    /* Transfer the i2c packets to the kernel and verify it worked */
    packets.msgs  = messages;
    packets.nmsgs = 1;
    if(ioctl(file, I2C_RDWR, &packets) < 0) {
        perror("Unable to send data");
        return 1;
    }

    return 0;
}


static int get_i2c_register(int file,
                            unsigned char addr,
                            unsigned char reg,
                            unsigned char *val) {
    unsigned char inbuf, outbuf;
    struct i2c_rdwr_ioctl_data packets;
    struct i2c_msg messages[2];

    /*
     * In order to read a register, we first do a "dummy write" by writing
     * 0 bytes to the register we want to read from.  This is similar to
     * the packet in set_i2c_register, except it's 1 byte rather than 2.
     */
    outbuf = reg;
    messages[0].addr  = addr;
    messages[0].flags = 0;
    messages[0].len   = sizeof(outbuf);
    messages[0].buf   = &outbuf;

    /* The data will get returned in this structure */
    messages[1].addr  = addr;
    messages[1].flags = I2C_M_RD/* | I2C_M_NOSTART*/;
    messages[1].len   = sizeof(inbuf);
    messages[1].buf   = &inbuf;

    /* Send the request to the kernel and get the result back */
    packets.msgs      = messages;
    packets.nmsgs     = 2;
    if(ioctl(file, I2C_RDWR, &packets) < 0) {
        perror("Unable to send data");
        return 1;
    }
    *val = inbuf;

    return 0;
}

int main()
{
    int fd_i2c = 0;
    int ret = -1;
    unsigned char val;
    fd_i2c = open(I2C_DEV_NAME, O_RDWR);
    if (fd_i2c < 0)
    {
        perror(I2C_DEV_NAME);
        goto clean;
    }
    
    while(1)
    {
        set_i2c_register(fd_i2c, BMP180_I2C_ADDR, 0xF4, 0x2E);
        get_i2c_register(fd_i2c, BMP180_I2C_ADDR, 0xF6, &val);
        printf("val: %d\n", val);
    }
    

    ret = 0;
clean:
    if (fd_i2c >= 0)
    {
        close(fd_i2c);
    }
    return ret;
}

status = "ok";