STM32F031使用内部时钟，配置为48M，但是SPI频率8分频后只有1M

密密123 · 发表于 2020-3-13 16:51:01

STM32F031使用内部晶振倍频到48M，在SPI配置中使用8分频。但是实际时钟只有1M。这是怎么回事呀？求解
时钟配置：
static void SetSysClock(void)
{
  __IO uint32_t StartUpCounter = 0, HSIStatus = 0;

  /* SYSCLK, HCLK, PCLK configuration ----------------------------------------*/
  /* Enable HSI */
  RCC->CR |= ((uint32_t)RCC_CR_HSION);//((uint32_t)RCC_CR_HSEON)

  /* Wait till HSI is ready and if Time out is reached exit */
  do
  {
HSIStatus = RCC->CR & RCC_CR_HSIRDY;//RCC->CR & RCC_CR_HSERDY;
StartUpCounter++;
  } while((HSIStatus == 0) && (StartUpCounter != HSI_STARTUP_TIMEOUT));

  if ((RCC->CR & RCC_CR_HSIRDY) != RESET)//((RCC->CR & RCC_CR_HSERDY) != RESET
  {
HSIStatus = (uint32_t)0x01;
  }
  else
  {
HSIStatus = (uint32_t)0x00;
  }

  if (HSIStatus == (uint32_t)0x01)
  {
/* Enable Prefetch Buffer and set Flash Latency */
FLASH->ACR = FLASH_ACR_PRFTBE | FLASH_ACR_LATENCY;

/* HCLK = SYSCLK */
RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1;

/* PCLK = HCLK */
RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE_DIV1;
/* PLL configuration = HSE * 6 = 48 MHz */
/* PLL configuration = HSI/2 * 12 = 48 MHz */
RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC  | RCC_CFGR_PLLMULL));
RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_HSI_DIV2| RCC_CFGR_PLLMULL12);
   // RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_PREDIV1 | RCC_CFGR_PLLXTPRE_PREDIV1 | RCC_CFGR_PLLMULL6)

/* Enable PLL */
RCC->CR |= RCC_CR_PLLON;

/* Wait till PLL is ready */
while((RCC->CR & RCC_CR_PLLRDY) == 0)
{
}

/* Select PLL as system clock source */
RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));
RCC->CFGR |= (uint32_t)RCC_CFGR_SW_PLL;

/* Wait till PLL is used as system clock source */
while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS) != (uint32_t)RCC_CFGR_SWS_PLL)
{
}
  }
  else
  { /* If HSI fails to start-up, the application will have wrong clock
      configuration. User can add here some code to deal with this error */
  }

}

SPI配置：
void SPI_GPIO_Configuration(void)
{
  GPIO_InitTypeDef GPIO_InitStructure;
   SPI_InitTypeDef  SPI_InitStructure;

   /* 使能AHB时钟 */
  RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOB, ENABLE);
RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);
   /* 使能APB2时钟 */
  RCC_APB2PeriphClockCmd(RCC_APB2Periph_SPI1, ENABLE);

  /*定义 SPI复用引脚 */
  GPIO_InitStructure.GPIO_Pin = PIN_SPI_SCK | PIN_SPI_MISO | PIN_SPI_MOSI;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;                      //复用模式
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;                //高速输出
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;                   //推完输出
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;                      //上拉
  GPIO_Init(PORT_SPI_SCK, &GPIO_InitStructure);

  GPIO_PinAFConfig(GPIOB, GPIO_PinSource4, GPIO_AF_0);
  GPIO_PinAFConfig(GPIOB, GPIO_PinSource5, GPIO_AF_0);
  GPIO_PinAFConfig(GPIOB, GPIO_PinSource3, GPIO_AF_0);

  /* 片选CS */
  GPIO_InitStructure.GPIO_Pin = PIN_SPI_CS;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;                   //输出模式
GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;                   //推完输出
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;                //高速输出
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;                      //上拉
  GPIO_Init(PORT_SPI_CS, &GPIO_InitStructure);

  /* SPI 初始化定义 */
  SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex; //SPI设置为双线双向全双工
  SPI_InitStructure.SPI_Mode = SPI_Mode_Master;                   //设置为主 SPI
  SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;                //SPI发送接收 8 位帧结构
  SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;                      //时钟悬空低
  SPI_InitStructure.SPI_CPHA = SPI_CPHA_2Edge;                      //数据捕获于第二个时钟沿
  SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;                         //软件控制 NSS 信号
  SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_8; //波特率预分频值为8
  SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;                //数据传输从 MSB 位开始
  SPI_InitStructure.SPI_CRCPolynomial = 7;                         //定义了用于 CRC值计算的多项式
  SPI_Init(SPI1, &SPI_InitStructure);

  SPI_RxFIFOThresholdConfig(SPI1, SPI_RxFIFOThreshold_QF);
  SPI_Cmd(SPI1, ENABLE);

// GPIO_SetBits(GPIOB, GPIO_Pin_15);
}

测试过系统时钟，内部时钟修改已成功，