STM3固件库2串口接收大于16位的字符串不使用中断

在STM32固件库V2中，可以使用DMA方式来接收串口数据，从而避免使用中断方式接收大于16位的字符串，同时又不会导致CPU占用率过高。以下是一个简单的示例代码，可以接收最多256个字节的数据：

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

#define USART_RX_BUF_SIZE 256

volatile uint8_t usart_rx_buf[USART_RX_BUF_SIZE];
volatile uint16_t usart_rx_buf_head = 0;
volatile uint16_t usart_rx_buf_tail = 0;

void USART2_DMA_Configuration(void)
{
    // 初始化DMA
    DMA_InitTypeDef DMA_InitStructure;
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA1, ENABLE);
    DMA_InitStructure.DMA_Channel = DMA_Channel_4;
    DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)&USART2->DR;
    DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t)usart_rx_buf;
    DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralToMemory;
    DMA_InitStructure.DMA_BufferSize = USART_RX_BUF_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_VeryHigh;
    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(DMA1_Stream5, &DMA_InitStructure);

    // 初始化中断
    NVIC_InitTypeDef NVIC_InitStructure;
    NVIC_InitStructure.NVIC_IRQChannel = DMA1_Stream5_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);

    DMA_ITConfig(DMA1_Stream5, DMA_IT_TC, ENABLE);

    // 启动DMA
    DMA_Cmd(DMA1_Stream5, ENABLE);
}

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

        uint16_t tail = usart_rx_buf_tail;
        uint16_t head = USART_RX_BUF_SIZE - DMA_GetCurrDataCounter(DMA1_Stream5);
        uint16_t count = (head >= tail) ? (head - tail) : (USART_RX_BUF_SIZE - tail + head);

        // 处理接收到的数据
        for (uint16_t i = 0; i < count; i++)
        {
            // 读取一个字节
            uint8_t data = usart_rx_buf[tail];
            tail = (tail + 1) % USART_RX_BUF_SIZE;

            // 处理数据
            printf("Received: %c\n", data);
        }

        usart_rx_buf_tail = tail;
    }
}

int main(void)
{
    // 初始化串口
    USART_InitTypeDef USART_InitStructure;
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART2, ENABLE);
    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(USART2, &USART_InitStructure);
    USART_Cmd(USART2, ENABLE);

    // 配置DMA
    USART2_DMA_Configuration();

    while (1)
    {
        // do something
    }
}

在此示例代码中，我们使用了DMA方式来接收串口数据，并使用循环缓冲区来存储接收到的数据。当DMA传输完成时，中断会触发并处理接收到的数据。由于使用了DMA方式，CPU不需要等待数据的到达，可以在数据到达时进行其他任务的处理，提高系统的实时性。