stm32体系时钟装备问题

体系从上电复位到72mz装备好之前，供给时钟的是内如高速rc振荡器供给8MZ的频率，这个由下面void SystemInit (void)函数的前面的一部分代码来完结的和确保的：

RCC->CR |= (uint32_t)0x00000001;

#ifndef STM32F10X_CL
RCC->CFGR &= (uint32_t)0xF8FF0000;
#else
RCC->CFGR &= (uint32_t)0xF0FF0000;
#endif


RCC->CR &= (uint32_t)0xFEF6FFFF;

RCC->CR &= (uint32_t)0xFFFBFFFF;

RCC->CFGR &= (uint32_t)0xFF80FFFF;

#ifdef STM32F10X_CL

RCC->CR &= (uint32_t)0xEBFFFFFF;

RCC->CIR = 0x00FF0000;

RCC->CFGR2 = 0x00000000;
#elif defined (STM32F10X_LD_VL) || defined (STM32F10X_MD_VL) || (defined STM32F10X_HD_VL)

RCC->CIR = 0x009F0000;

RCC->CFGR2 = 0x00000000;
#else

RCC->CIR = 0x009F0000;
#endif

#if defined (STM32F10X_HD) || (defined STM32F10X_XL) || (defined STM32F10X_HD_VL)
#ifdef DATA_IN_ExtSRAM
SystemInit_ExtMemCtl();
#endif
#endif

接着void SystemInit (void)调用 SetSysClock();函数，将体系时钟装备到72m，将AHB,APB1，APB2等外设之前的时钟都装备好，然后切换到72mz下运转。所以在运用哪个外设的时分，只需要使能相应的外设时钟就可以了