背景：

项目需求，需检测是否有camera sensor(CHIP_ADDR:0x6C>>1),
通过I2C读取sensor的CHIP ID(CHIP_ID_H:0x300A, CHIP_ID_L:0x300B)为0x27 0x70

应用层I2C操作:

    unsigned char rddata[2]={0};
    unsigned char rdaddr0[2] = {0x30, 0x0A}; //CHIP_ID_H  0x27
    unsigned char rdaddr1[2] = {0x30, 0x0B}; //CHIP_ID_L  0x70
    int fd =open(CHIP, O_RDWR);
    if (fd< 0) {
        printf("open"CHIP"failed\n");        
        return -1;
    }
#if 0  //方式一
    if (ioctl(fd, I2C_SLAVE_FORCE, CHIP_ADDR) < 0) { 
        /* 设置芯片地址 */
        printf("oictl:setslave address failed\n");
        close(fd);
        return 0;
    }
    struct i2c_msg msg;    
    
    printf("writeaddress return: %d\n",write(fd, rdaddr0, 2)); /* 读取寄存器地址 */
    printf("readdata return:%d\n", read(fd, &rddata[1], 1));
    printf("writeaddress return: %d\n",write(fd, rdaddr1, 2)); // 读取寄存器地址
    printf("readdata return:%d\n", read(fd, &rddata[0], 1));
    
#endif
#if 1 //方式二
    struct i2c_msg msgs[2];
    struct i2c_rdwr_ioctl_data ioctl_data;
    
    msgs[0].addr= CHIP_ADDR;  
    msgs[0].flags = 0;//write
    msgs[0].len= 2;
    msgs[0].buf= rdaddr0;
    msgs[1].addr= CHIP_ADDR;
    msgs[1].flags|= I2C_M_RD;
    msgs[1].len= 1;
    msgs[1].buf= &rddata[1];
    ioctl_data.nmsgs= 2;
    ioctl_data.msgs= msgs;
    printf("ioctlwrite address, return :%d\n", ioctl(fd, I2C_RDWR, &ioctl_data));

    msgs[0].buf= rdaddr1;
    msgs[1].buf= &rddata[0];
    printf("ioctlwrite address, return :%d\n", ioctl(fd, I2C_RDWR, &ioctl_data));
    
#endif
    printf("rddata:%02x %02x\n", rddata[1], rddata[0]);
    close(fd);
    if((rddata[1]==0x27)&&(rddata[0]==0x70))
    {
        return 1;
    }
    
    return 0;