演示 USART1 当接收缓冲器满时，将接收到的数据传送出去V6-LED1闪烁表示正在收发数据。-When the receive buffer USART1 demo full, will receive the data transmitted V6-LED1 flashes that are sending and receiving data.

STM32 中使用USART2中断接收，让后USART1使用DMA的方式发送出去-Used in the STM32 USART2 interrupt receiving, let USART1 using DMA way after send out