STM32L071 DMA串口收发

使用DMA中断接收串口 不定量数据

设置如下：

1. 接收中断增加
    void HAL_UART_IRQHandler(UART_HandleTypeDef *huart)
    增加
    if(((isrflags & USART_ISR_IDLE) != RESET) && ((cr1its & USART_CR1_IDLEIE) != RESET))
     {
    //Record the received bytes number
     Rev_Size = huart->RxXferSize - huart->hdmarx->Instance->CNDTR;
    //clear the IDLE flag
    __HAL_UART_CLEAR_IDLEFLAG(huart);
    //Abord the received process
    HAL_UART_AbortReceive_IT(huart);
     return;
     }

2. DMA接收增加
    HAL_StatusTypeDef HAL_UART_Receive_DMA(UART_HandleTypeDef *huart, uint8_t *pData, uint16_t Size)

    //Modification 1
    SET_BIT(huart->Instance->CR1, USART_CR1_IDLEIE);

3. 空闲中断改动
    HAL_StatusTypeDef HAL_UART_AbortReceive_IT(UART_HandleTypeDef *huart)

    //ATOMIC_CLEAR_BIT(huart->Instance->CR1, (USART_CR1_RXN