STM32 SPI和DMA的初始化时间是多少，SPI使用DMA时，初始化以及使能的顺序应该如何，使用标准库给出代码

SPI和DMA初始化的时间取决于具体的芯片型号和系统时钟频率等因素，无法给出具体的时间。一般而言，SPI和DMA的初始化时间不会太长，可以通过合理的代码设计和优化来缩短初始化时间。

当使用SPI和DMA时，初始化和使能的顺序应该如下：

1. 初始化SPI外设，包括设置SPI时钟、模式、数据位数、使能硬件控制CS等参数。

2. 初始化DMA，包括设置DMA通道、数据传输方向、数据宽度、缓存地址等参数。

3. 使能DMA通道，开始DMA传输。

下面是使用STM32标准库初始化SPI和DMA的示例代码：

#include "stm32f4xx.h"
#include "stm32f4xx_spi.h"
#include "stm32f4xx_dma.h"

#define SPIx                    SPI1
#define SPIx_CLK                RCC_APB2Periph_SPI1
#define SPIx_IRQn               SPI1_IRQn
#define SPIx_IRQHandler         SPI1_IRQHandler

#define DMAx_CLK                RCC_AHB1Periph_DMA2
#define DMAx_CHANNEL            DMA_Channel_3
#define DMAx_STREAM             DMA2_Stream3
#define DMAx_STREAM_IRQn        DMA2_Stream3_IRQn
#define DMAx_STREAM_IRQHandler  DMA2_Stream3_IRQHandler

uint8_t txBuffer[10];
uint8_t rxBuffer[10];

void SPIx_Init(void)
{
  SPI_InitTypeDef  SPI_InitStructure;
  GPIO_InitTypeDef GPIO_InitStructure;

  /* Enable GPIO clock */
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);

  /* Enable SPI clock */
  RCC_APB2PeriphClockCmd(SPIx_CLK, ENABLE);

  /* Configure SPI pins */
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5 | GPIO_Pin_6 | GPIO_Pin_7;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_PuPd  = GPIO_PuPd_DOWN;
  GPIO_Init(GPIOA, &GPIO_InitStructure);

  /* Connect SPI pins to AF */
  GPIO_PinAFConfig(GPIOA, GPIO_PinSource5, GPIO_AF_SPI1);
  GPIO_PinAFConfig(GPIOA, GPIO_PinSource6, GPIO_AF_SPI1);
  GPIO_PinAFConfig(GPIOA, GPIO_PinSource7, GPIO_AF_SPI1);

  /* SPI configuration */
  SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;
  SPI_InitStructure.SPI_Mode = SPI_Mode_Master;
  SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;
  SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;
  SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge;
  SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;
  SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_4;
  SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;
  SPI_InitStructure.SPI_CRCPolynomial = 7;
  SPI_Init(SPIx, &SPI_InitStructure);

  /* Enable SPI */
  SPI_Cmd(SPIx, ENABLE);
}

void DMAx_Init(void)
{
  DMA_InitTypeDef DMA_InitStructure;

  /* Enable DMA clock */
  RCC_AHB1PeriphClockCmd(DMAx_CLK, ENABLE);

  /* DMA configuration */
  DMA_InitStructure.DMA_Channel = DMAx_CHANNEL;
  DMA_InitStructure.DMA_PeripheralBaseAddr = (uint32_t)&(SPIx->DR);
  DMA_InitStructure.DMA_Memory0BaseAddr = (uint32_t)rxBuffer;
  DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralToMemory;
  DMA_InitStructure.DMA_BufferSize = sizeof(rxBuffer);
  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_Normal;
  DMA_InitStructure.DMA_Priority = DMA_Priority_High;
  DMA_InitStructure.DMA_FIFOMode = DMA_FIFOMode_Disable;
  DMA_InitStructure.DMA_FIFOThreshold = DMA_FIFOThreshold_HalfFull;
  DMA_InitStructure.DMA_MemoryBurst = DMA_MemoryBurst_Single;
  DMA_InitStructure.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;
  DMA_Init(DMAx_STREAM, &DMA_InitStructure);

  /* Enable DMA interrupts */
  DMA_ITConfig(DMAx_STREAM, DMA_IT_TC, ENABLE);
  NVIC_EnableIRQ(DMAx_STREAM_IRQn);
}

void DMAx_Start(void)
{
  /* Enable DMA channel */
  DMA_Cmd(DMAx_STREAM, ENABLE);

  /* Start SPI communication */
  SPI_I2S_DMACmd(SPIx, SPI_I2S_DMAReq_Rx, ENABLE);
  SPI_I2S_SendData(SPIx, txBuffer[0]);
}

void DMAx_Stop(void)
{
  /* Disable DMA channel */
  DMA_Cmd(DMAx_STREAM, DISABLE);

  /* Disable SPI communication */
  SPI_I2S_DMACmd(SPIx, SPI_I2S_DMAReq_Rx, DISABLE);
}

void SPIx_DMA_Rx_Callback(void)
{
  /* DMA transfer complete */
}

void DMAx_STREAM_IRQHandler(void)
{
  if (DMA_GetITStatus(DMAx_STREAM, DMA_IT_TCIF3))
  {
    /* Clear DMA interrupt flag */
    DMA_ClearITPendingBit(DMAx_STREAM, DMA_IT_TCIF3);

    /* DMA transfer complete callback */
    SPIx_DMA_Rx_Callback();
  }
}

int main(void)
{
  /* Initialize SPI and DMA */
  SPIx_Init();
  DMAx_Init();

  /* Start DMA transfer */
  DMAx_Start();

  /* Wait for DMA transfer to complete */
  while (DMA_GetFlagStatus(DMAx_STREAM, DMA_FLAG_TCIF3) == RESET);

  /* Stop DMA transfer */
  DMAx_Stop();

  while (1);
}

以上代码仅供参考，具体的实现方式需要根据实际需求进行调整。