`static rtems_libi2c_tfr_mode_t tfr_mode = {
  .baudrate = 20000000,
  .bits_per_char = 8,
  .lsb_first = FALSE,
  .clock_inv = TRUE,
  .clock_phs = FALSE
};

static rtems_status_code spi_mcp4822_write(
  rtems_device_major_number major,
  rtems_device_minor_number minor,
  void *arg
) {
	rtems_status_code sc = RTEMS_SUCCESSFUL;
	rtems_libio_rw_args_t *rwargs = arg;
	int cnt = rwargs -> count;
	unsigned char *buf = (unsigned char *) rwargs -> buffer;
	/*send start*/
	sc = rtems_libi2c_send_start(minor);
	if(sc<0){
		printf("send start error \n");
		fflush(stdout);
		return sc;
	}else{
		printf("start sended \n");
		fflush(stdout);
	}
	/* ioctl*/
	sc = rtems_libi2c_ioctl(minor, RTEMS_LIBI2C_IOCTL_SET_TFRMODE, &tfr_mode);
	 if ( sc != RTEMS_SUCCESSFUL ) {
		printf("ioctl error \n");
		fflush(stdout);
	    return sc;
	 }else{
		printf("ioctl setted \n");
		fflush(stdout);
	 }
	/*send addr*/
	sc = rtems_libi2c_send_addr(minor, FALSE);
      if ( sc != RTEMS_SUCCESSFUL ) {
          printf("send address error \n");
	  fflush(stdout);
         return sc;
      }else{
         printf("address sended \n");
	 fflush(stdout);
    }

	/*write bytes*/
	int data_sent_cnt = rtems_libi2c_write_bytes(minor, buf, cnt);
    if (data_sent_cnt < 0) {
	  printf("write bytes error \n");
	  fflush(stdout);
          return RTEMS_IO_ERROR;
    }else{
          printf("wrote %d bytes \n", data_sent_cnt);
          fflush(stdout);
    }
	/*send stop*/
    sc = rtems_libi2c_send_stop(minor);
    if ( sc != RTEMS_SUCCESSFUL ) {
	  printf("send stop error \n");
	  fflush(stdout);
         return sc;
    }else{
	printf("stop sended \n");
	fflush(stdout);
    }
	return RTEMS_SUCCESSFUL;
}

/*read not used, data cannot be read from mcp4822 */
static rtems_status_code spi_mcp4822_read(
  rtems_device_major_number major,
  rtems_device_minor_number minor,
  void *arg
) {
  rtems_status_code sc = RTEMS_SUCCESSFUL;
  return sc;
};
...`