STM32F407使用标准库，usart2通过DMA进行数据的接收，接收缓冲区使用乒乓缓存的实例

下面是一个使用标准库，usart2通过DMA进行数据接收，并使用乒乓缓存的实例代码：

首先需要初始化USART2和DMA：

#include "stm32f4xx.h"
#include <stdio.h>

#define RX_BUFFER_SIZE 64

uint8_t rxBuffer1[RX_BUFFER_SIZE];
uint8_t rxBuffer2[RX_BUFFER_SIZE];
uint8_t* currentRxBuffer;

void initUSART2(void)
{
    GPIO_InitTypeDef GPIO_InitStruct;
    USART_InitTypeDef USART_InitStruct;
    NVIC_InitTypeDef NVIC_InitStruct;
    DMA_InitTypeDef DMA_InitStruct;

    /* Enable clock for GPIOA and USART2 */
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2, ENABLE);

    /* Configure PA2 and PA3 for USART2 TX and RX */
    GPIO_InitStruct.GPIO_Pin = GPIO_Pin_2 | GPIO_Pin_3;
    GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF;
    GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStruct.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStruct.GPIO_PuPd = GPIO_PuPd_UP;
    GPIO_Init(GPIOA, &GPIO_InitStruct);

    /* Connect PA2 to USART2_TX */
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource2, GPIO_AF_USART2);

    /* Connect PA3 to USART2_RX */
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource3, GPIO_AF_USART2);

    /* Configure USART2 */
    USART_InitStruct.USART_BaudRate = 9600;
    USART_InitStruct.USART_WordLength = USART_WordLength_8b;
    USART_InitStruct.USART_StopBits = USART_StopBits_1;
    USART_InitStruct.USART_Parity = USART_Parity_No;
    USART_InitStruct.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
    USART_InitStruct.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
    USART_Init(USART2, &USART_InitStruct);
    USART_Cmd(USART2, ENABLE);

    /* Configure DMA */
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA1, ENABLE);

    DMA_InitStruct.DMA_Channel = DMA_Channel_4;
    DMA_InitStruct.DMA_PeripheralBaseAddr = (uint32_t)&USART2->DR;
    DMA_InitStruct.DMA_Memory0BaseAddr = (uint32_t)rxBuffer1;
    DMA_InitStruct.DMA_DIR = DMA_DIR_PeripheralToMemory;
    DMA_InitStruct.DMA_BufferSize = RX_BUFFER_SIZE;
    DMA_InitStruct.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
    DMA_InitStruct.DMA_MemoryInc = DMA_MemoryInc_Enable;
    DMA_InitStruct.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;
    DMA_InitStruct.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;
    DMA_InitStruct.DMA_Mode = DMA_Mode_Circular;
    DMA_InitStruct.DMA_Priority = DMA_Priority_High;
    DMA_InitStruct.DMA_FIFOMode = DMA_FIFOMode_Disable;
    DMA_InitStruct.DMA_FIFOThreshold = DMA_FIFOThreshold_HalfFull;
    DMA_InitStruct.DMA_MemoryBurst = DMA_MemoryBurst_Single;
    DMA_InitStruct.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;
    DMA_Init(DMA1_Stream5, &DMA_InitStruct);

    /* Enable DMA interrupts */
    DMA_ITConfig(DMA1_Stream5, DMA_IT_TC, ENABLE);

    /* Configure NVIC for DMA interrupts */
    NVIC_InitStruct.NVIC_IRQChannel = DMA1_Stream5_IRQn;
    NVIC_InitStruct.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStruct.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStruct);

    /* Start DMA */
    DMA_Cmd(DMA1_Stream5, ENABLE);

    /* Set currentRxBuffer to rxBuffer1 */
    currentRxBuffer = rxBuffer1;
}

在DMA中断服务程序中，需要判断当前DMA传输的缓冲区，并根据情况切换到另一个缓冲区：

void DMA1_Stream5_IRQHandler(void)
{
    if (DMA_GetITStatus(DMA1_Stream5, DMA_IT_TCIF5) != RESET)
    {
        DMA_ClearITPendingBit(DMA1_Stream5, DMA_IT_TCIF5);

        /* Switch to the other buffer */
        if (currentRxBuffer == rxBuffer1)
        {
            DMA1_Stream5->M0AR = (uint32_t)rxBuffer2;
            currentRxBuffer = rxBuffer2;
        }
        else
        {
            DMA1_Stream5->M0AR = (uint32_t)rxBuffer1;
            currentRxBuffer = rxBuffer1;
        }
    }
}

在主函数中，可以使用`currentRxBuffer`指向当前接收到的数据缓冲区：

int main(void)
{
    initUSART2();

    while (1)
    {
        /* Process received data from currentRxBuffer */
    }
}