gistfile1.txt

          // Read current external display brightness
          data[0] = 0x82;
          data[1] = 0x01;
          data[2] = BRIGHTNESS;

          err = IOAVServiceWriteI2C(avService, 0x37, 0x00, data, 3);
          if (err) {
            NSLog(@"Something went wrong: %s", mach_error_string(err));
            return 1;
          }
          usleep(35000);

          err = IOAVServiceReadI2C(avService, 0x37, 0x00, data, 12);
          if (err) {
            NSLog(@"Something went wrong: %s", mach_error_string(err));
            return 1;
          }
          usleep(35000);

          NSLog(@"External display brightness read: %d", data[9]);

          if (data[9] != out_brightness) {
            NSLog(@"Setting brightness to %d for %@", out_brightness,
                  avService);
            data[0] = 0x84;
            data[1] = 0x03;
            data[2] = BRIGHTNESS;
            data[3] = 0x00;
            data[4] = out_brightness;

            err = IOAVServiceWriteI2C(avService, 0x37, 0x00, data, 5);
            if (err) {
              NSLog(@"Something went wrong: %s", mach_error_string(err));
              return 1;
            }