예제 (TCN75)

I2C 인터페이스인 TCN75 칩의 온도를 가져오기 위한 응용이다.

...
#define I2C_ADDR_TCN75 0x4f  // 하드웨어 설계에 따라 달라진다.
...

void tcn75_init(void)
{
    int fd;

    fd = open("/dev/i2c-0", O_RDWR); // mknod /dev/i2c-0 c 89 0
    if(fd < 0) {
        fprintf(stderr, "can't open /dev/i2c-0\n");
        exit(2);
    }

    ioctl(fd, I2C_SLAVE, I2C_ADDR_TCN75);

    unsigned char cmd, read_data[2];
    int read_value;
    cmd = 0x00; // TEMP
    write(fd, &cmd, 1); // Pointer Byte
    close(fd);
}

float tcn75_get_temperature(void)
{
    int fd;

    fd = open("/dev/i2c-0", O_RDWR);
    if(fd < 0) {
        fprintf(stderr, "can't open /dev/i2c-0\n");
        exit(2);
    }

    ioctl(fd, I2C_SLAVE, I2C_ADDR_TCN75);

    unsigned char read_data[2];
    int read_value;
    float temperature;
    read(fd, read_data, 2);
    read_value = (read_data[0]<<8) | read_data[1];
    read_value >>= 7;
    if(read_value > 256) read_value = read_value - 512;
    temperature = read_value / 2.0;
    close(fd);
    return temperature;
}


int main(int argc, char** argv)
{
    tcn75_init();
    while(1) {
        printf("temp = %f\n", tcn75_get_temperature());
        sleep(1);
    }
    return 0;
}