当出现这个问题时，往往是因为你没有在RCC寄存器中把相关的时钟使能打开。
配置寄存器之前记得调用"RCC_AxxxPeriphClockCmd"先打开需要配置的时钟源，别调用了“RCC_AxxxPeriphResetCmd"。
相关函数定义源代码如下：
/**
* @brief Enables or disables the AHB peripheral clock.
* @param RCC_AHBPeriph: specifies the AHB peripheral to gates its clock.
*
* For @b STM32_Connectivity_line_devices, this parameter can be any combination
* of the following values:
* @arg RCC_AHBPeriph_DMA1
* @arg RCC_AHBPeriph_DMA2
* @arg RCC_AHBPeriph_SRAM
* @arg RCC_AHBPeriph_FLITF
* @arg RCC_AHBPeriph_CRC
* @arg RCC_AHBPeriph_OTG_FS
* @arg RCC_AHBPeriph_ETH_MAC
* @arg RCC_AHBPeriph_ETH_MAC_Tx
* @arg RCC_AHBPeriph_ETH_MAC_Rx
*
* For @b other_STM32_devices, this parameter can be any combination of the
* following values:
* @arg RCC_AHBPeriph_DMA1
* @arg RCC_AHBPeriph_DMA2
* @arg RCC_AHBPeriph_SRAM
* @arg RCC_AHBPeriph_FLITF
* @arg RCC_AHBPeriph_CRC
* @arg RCC_AHBPeriph_FSMC
* @arg RCC_AHBPeriph_SDIO
*
* @note SRAM and FLITF clock can be disabled only during sleep mode.
* @param NewState: new state of the specified peripheral clock.
* This parameter can be: ENABLE or DISABLE.
* @retval None
*/
void RCC_AHBPeriphClockCmd(uint32_t RCC_AHBPeriph, FunctionalState NewState)
{
/* Check the parameters */
assert_param(IS_RCC_AHB_PERIPH(RCC_AHBPeriph));
assert_param(IS_FUNCTIONAL_STATE(NewState)); if (NewState != DISABLE)
{
RCC->AHBENR |= RCC_AHBPeriph;
}
else
{
RCC->AHBENR &= ~RCC_AHBPeriph;
}
} /**
* @brief Enables or disables the High Speed APB (APB2) peripheral clock.
* @param RCC_APB2Periph: specifies the APB2 peripheral to gates its clock.
* This parameter can be any combination of the following values:
* @arg RCC_APB2Periph_AFIO, RCC_APB2Periph_GPIOA, RCC_APB2Periph_GPIOB,
* RCC_APB2Periph_GPIOC, RCC_APB2Periph_GPIOD, RCC_APB2Periph_GPIOE,
* RCC_APB2Periph_GPIOF, RCC_APB2Periph_GPIOG, RCC_APB2Periph_ADC1,
* RCC_APB2Periph_ADC2, RCC_APB2Periph_TIM1, RCC_APB2Periph_SPI1,
* RCC_APB2Periph_TIM8, RCC_APB2Periph_USART1, RCC_APB2Periph_ADC3,
* RCC_APB2Periph_TIM15, RCC_APB2Periph_TIM16, RCC_APB2Periph_TIM17,
* RCC_APB2Periph_TIM9, RCC_APB2Periph_TIM10, RCC_APB2Periph_TIM11
* @param NewState: new state of the specified peripheral clock.
* This parameter can be: ENABLE or DISABLE.
* @retval None
*/
void RCC_APB2PeriphClockCmd(uint32_t RCC_APB2Periph, FunctionalState NewState)
{
/* Check the parameters */
assert_param(IS_RCC_APB2_PERIPH(RCC_APB2Periph));
assert_param(IS_FUNCTIONAL_STATE(NewState));
if (NewState != DISABLE)
{
RCC->APB2ENR |= RCC_APB2Periph;
}
else
{
RCC->APB2ENR &= ~RCC_APB2Periph;
}
} /**
* @brief Enables or disables the Low Speed APB (APB1) peripheral clock.
* @param RCC_APB1Periph: specifies the APB1 peripheral to gates its clock.
* This parameter can be any combination of the following values:
* @arg RCC_APB1Periph_TIM2, RCC_APB1Periph_TIM3, RCC_APB1Periph_TIM4,
* RCC_APB1Periph_TIM5, RCC_APB1Periph_TIM6, RCC_APB1Periph_TIM7,
* RCC_APB1Periph_WWDG, RCC_APB1Periph_SPI2, RCC_APB1Periph_SPI3,
* RCC_APB1Periph_USART2, RCC_APB1Periph_USART3, RCC_APB1Periph_USART4,
* RCC_APB1Periph_USART5, RCC_APB1Periph_I2C1, RCC_APB1Periph_I2C2,
* RCC_APB1Periph_USB, RCC_APB1Periph_CAN1, RCC_APB1Periph_BKP,
* RCC_APB1Periph_PWR, RCC_APB1Periph_DAC, RCC_APB1Periph_CEC,
* RCC_APB1Periph_TIM12, RCC_APB1Periph_TIM13, RCC_APB1Periph_TIM14
* @param NewState: new state of the specified peripheral clock.
* This parameter can be: ENABLE or DISABLE.
* @retval None
*/
void RCC_APB1PeriphClockCmd(uint32_t RCC_APB1Periph, FunctionalState NewState)
{
/* Check the parameters */
assert_param(IS_RCC_APB1_PERIPH(RCC_APB1Periph));
assert_param(IS_FUNCTIONAL_STATE(NewState));
if (NewState != DISABLE)
{
RCC->APB1ENR |= RCC_APB1Periph;
}
else
{
RCC->APB1ENR &= ~RCC_APB1Periph;
}
}