rt_printf功能与其他串口功能，RA6M4

rt_sem_init(&rx_sem, "rx_sem", 0, RT_IPC_FLAG_FIFO);
rt_device_control(serial, RT_DEVICE_CTRL_CONFIG, &config);//串口参数写入
rt_device_open(serial, RT_DEVICE_FLAG_INT_RX | RT_DEVICE_OFLAG_RDWR );
rt_device_set_rx_indicate(serial, uart_recv_callback);//设置串口中断接收回调函数
rt_device_write(serial, 0, str, (sizeof(str) - 1));

/* Call the transmit interface for transmission */
 serial->ops->transmit(serial,
                          (rt_uint8_t *)buffer,
                          size,
                          RT_SERIAL_TX_BLOCKING);