写一段DMA的串口接收例子

以下是一段DMA串口接收的例子：

#include "stm32f4xx.h"

#define BUFFER_SIZE 256

uint8_t rx_buffer[BUFFER_SIZE];

void DMA2_Stream2_IRQHandler(void)
{
    if (DMA_GetITStatus(DMA2_Stream2, DMA_IT_TCIF2))
    {
        DMA_ClearITPendingBit(DMA2_Stream2, DMA_IT_TCIF2);
        USART_ClearFlag(USART1, USART_FLAG_TC);
    }
}

void USART1_IRQHandler(void)
{
    if (USART_GetITStatus(USART1, USART_IT_IDLE) != RESET)
    {
        DMA_Cmd(DMA2_Stream2, DISABLE);
        DMA_ClearFlag(DMA2_Stream2, DMA_FLAG_TCIF2);
        DMA_SetCurrDataCounter(DMA2_Stream2, BUFFER_SIZE);
        DMA_Cmd(DMA2_Stream2, ENABLE);
        USART_ClearITPendingBit(USART1, USART_IT_IDLE);
    }
}

int main(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    USART_InitTypeDef USART_InitStructure;
    DMA_InitTypeDef DMA_InitStructure;
    NVIC_InitTypeDef NVIC_InitStructure;

    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA2, ENABLE);

    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9 | GPIO_Pin_10;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
    GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    GPIO_PinAFConfig(GPIOA, GPIO_PinSource9, GPIO_AF_USART1);
    GPIO_PinAFConfig(GPIOA, GPIO_PinSource10, GPIO_AF_USART1);

    USART_InitStructure.USART_BaudRate = 115200;
    USART_InitStructure.USART_WordLength = USART_WordLength_8b;
    USART_InitStructure.USART_StopBits = USART_StopBits_1;
    USART_InitStructure.USART_Parity = USART_Parity_No;
    USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
    USART_InitStructure.USART_Mode = USART_Mode_Rx | USART_Mode_Tx;
    USART_Init(USART1, &USART_InitStructure);

    DMA_InitStructure.DMA_Channel = DMA_Channel_4;
    DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t) & (USART1->DR);
    DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t)rx_buffer;
    DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralToMemory;
    DMA_InitStructure.DMA_BufferSize = BUFFER_SIZE;
    DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
    DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
    DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_Byte;
    DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_Byte;
    DMA_InitStructure.DMA_Mode = DMA_Mode_Circular;
    DMA_InitStructure.DMA_Priority = DMA_Priority_High;
    DMA_InitStructure.DMA_FIFOMode = DMA_FIFOMode_Disable;
    DMA_InitStructure.DMA_FIFOThreshold = DMA_FIFOThreshold_Full;
    DMA_InitStructure.DMA_MemoryBurst = DMA_MemoryBurst_Single;
    DMA_InitStructure.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;
    DMA_Init(DMA2_Stream2, &DMA_InitStructure);

    USART_DMACmd(USART1, USART_DMAReq_Rx, ENABLE);

    NVIC_InitStructure.NVIC_IRQChannel = DMA2_Stream2_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);

    NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);

    DMA_Cmd(DMA2_Stream2, ENABLE);
    USART_Cmd(USART1, ENABLE);

    while (1)
    {
        // do something
    }
}

这段代码实现了使用 DMA 接收串口数据，并将数据存储在 rx_buffer 中。当 DMA 接收完成时，会触发 DMA2_Stream2_IRQHandler 中断，我们可以在中断处理函数中对接收到的数据进行处理。USART1_IRQHandler 中断用于检测串口空闲中断，当串口空闲时，表示一帧数据已经接收完成，我们可以在中断处理函数中重新配置 DMA，以便继续接收下一帧数据。