平时都用的8N1的模式，这次使用了校验位，因此串口的初始化工作需要改变

#ifdef RT_USING_UART2
USART_InitStructure.USART_BaudRate = 9600;
USART_InitStructure.USART_WordLength = USART_WordLength_9b;
USART_InitStructure.USART_StopBits = USART_StopBits_2;
USART_InitStructure.USART_Parity = USART_Parity_Even;
USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
USART_ClockInitStructure.USART_Clock = USART_Clock_Disable;
USART_ClockInitStructure.USART_CPOL = USART_CPOL_Low;
USART_ClockInitStructure.USART_CPHA = USART_CPHA_2Edge;
USART_ClockInitStructure.USART_LastBit = USART_LastBit_Disable;
USART_Init(USART2, &USART_InitStructure);
USART_ClockInit(USART2, &USART_ClockInitStructure);

/* register uart2 */
rt_hw_serial_register(&uart2_device, "uart2",
RT_DEVICE_FLAG_RDWR | RT_DEVICE_FLAG_INT_RX | RT_DEVICE_FLAG_STREAM,
&uart2);

/* Enable USART2 DMA Rx request */
USART_ITConfig(USART2, USART_IT_RXNE, ENABLE);
#endif

这里最重要的是

这个字段意思是字的长度，没有校验位的时候是8位，有了之后要加一位。因此，这不代表数据的长度……真坑

还要多些网友的帮助，详见

http://www.rt-thread.org/phpBB3/viewtopic.php?f=2&t=2960&p=16419#p16419