求助，STM32库函数RCC

Posted 2023-04-09

参考技术A 看模板中main函数里这么一段代码
int main(void)

/*!< At this stage the microcontroller clock setting is already configured,
this is done through SystemInit() function which is called from startup
file (startup_stm32f10x_xx.s) before to branch to application main.
To reconfigure the default setting of SystemInit() function, refer to
system_stm32f10x.c file
*/
也就是说，进入main函数前，系统已经做了时钟配置，调用的是SystemInit()函数，那么我们就进入此函数看过究竟。

void SystemInit (void)

/* Reset the RCC clock configuration to the default reset state(for debug purpose) */
/* Set HSION bit */
RCC->CR |= (uint32_t)0x00000001;
/* Reset SW, HPRE, PPRE1, PPRE2, ADCPRE and MCO bits */
#ifndef STM32F10X_CL
RCC->CFGR &= (uint32_t)0xF8FF0000;
#else
RCC->CFGR &= (uint32_t)0xF0FF0000;
#endif /* STM32F10X_CL */

/* Reset HSEON, CSSON and PLLON bits */
RCC->CR &= (uint32_t)0xFEF6FFFF;
/* Reset HSEBYP bit */
RCC->CR &= (uint32_t)0xFFFBFFFF;
/* Reset PLLSRC, PLLXTPRE, PLLMUL and USBPRE/OTGFSPRE bits */
RCC->CFGR &= (uint32_t)0xFF80FFFF;
#ifdef STM32F10X_CL
/* Reset PLL2ON and PLL3ON bits */
RCC->CR &= (uint32_t)0xEBFFFFFF;
/* Disable all interrupts and clear pending bits */
RCC->CIR = 0x00FF0000;
/* Reset CFGR2 register */
RCC->CFGR2 = 0x00000000;
#elif defined (STM32F10X_LD_VL) || defined (STM32F10X_MD_VL) || (defined STM32F10X_HD_VL)
/* Disable all interrupts and clear pending bits */
RCC->CIR = 0x009F0000;
/* Reset CFGR2 register */
RCC->CFGR2 = 0x00000000;
#else
/* Disable all interrupts and clear pending bits */
RCC->CIR = 0x009F0000;
#endif /* STM32F10X_CL */

#if defined (STM32F10X_HD) || (defined STM32F10X_XL) || (defined STM32F10X_HD_VL)
#ifdef DATA_IN_ExtSRAM
SystemInit_ExtMemCtl();
#endif /* DATA_IN_ExtSRAM */
#endif
/* Configure the System clock frequency, HCLK, PCLK2 and PCLK1 prescalers */
/* Configure the Flash Latency cycles and enable prefetch buffer */
SetSysClock();
#ifdef VECT_TAB_SRAM
SCB->VTOR = SRAM_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal SRAM. */
#else
SCB->VTOR = FLASH_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal FLASH. */
#endif

其他的我先都不想管，我就看准了这几句：
/* Configure the System clock frequency, HCLK, PCLK2 and PCLK1 prescalers */
那么就是告诉我们，给HCLK、PCLK1和PCLK2的配置是调用 SetSysClock()函数了。
继续跟进此函数，如下：
static void SetSysClock(void)

#ifdef SYSCLK_FREQ_HSE
SetSysClockToHSE();
#elif defined SYSCLK_FREQ_24MHz
SetSysClockTo24();
#elif defined SYSCLK_FREQ_36MHz
SetSysClockTo36();
#elif defined SYSCLK_FREQ_48MHz
SetSysClockTo48();
#elif defined SYSCLK_FREQ_56MHz
SetSysClockTo56();
#elif defined SYSCLK_FREQ_72MHz
SetSysClockTo72();
#endif

/* If none of the define above is enabled, the HSI is used as System clock
source (default after reset) */

这其实就告诉我们，SYSCLK的设置就是根据我们定义来设定，如果定义了SYSCLK_FREQ_HSE
，那么SYSCLK就是HSE（默认8MHz），如果定义了SYSCLK_FREQ_24MHz，那么SYSCLK就是24MHz，一次类推。而设置时钟是靠SetSysClockToXX()函数来实现的！
好了，既然这样，我就想继续跟进，去找SetSysClockToXX()，但是惊讶地发现，提示此函数没有定义！为啥，那是因为我去找的刚好是未被编译的，当然找不到定义，事实上这些XX函数都存在在system_stm32f10x.c文件中，但是只有一个能被跟踪找到，那就是对应的宏被定义了的那个。这些定义到底在哪？跟进！得到如下：
//system_stm32f10x.c文件
#if defined (STM32F10X_LD_VL) || (defined STM32F10X_MD_VL) || (defined STM32F10X_HD_VL)
/* #define SYSCLK_FREQ_HSE HSE_VALUE */
#define SYSCLK_FREQ_24MHz 24000000
#else
/* #define SYSCLK_FREQ_HSE HSE_VALUE */
/* #define SYSCLK_FREQ_24MHz 24000000 */
/* #define SYSCLK_FREQ_36MHz 36000000 */
/* #define SYSCLK_FREQ_48MHz 48000000 */
/* #define SYSCLK_FREQ_56MHz 56000000 */
#define SYSCLK_FREQ_72MHz 72000000
#endif
这下我想起来了，每次用keil建立工程，总是要求预先定义两个宏：USE_STDPERIPH_DRIVER和STM32F10X_MD,原来这儿就体现出作用了！
因为我的芯片是STM32F10X_MD型，所以SYSCLK就被选择了72MHz!
至于static void SetSysClockTo72(void)此函数到底是怎么把SYSCLK设置成为72MHz的，我懒得去管了，代码很长，也在system_stm32f10x.c文件中，说实话我真没兴趣去搞明白，但要知道，在这个函数里，顺便把HLCK、PCLK1和PCLK2都做了默认设置！
话说回来，我真不想去看寄存器操作的，但是，这个函数里面有一个我认为是ST公司的工程师们大意写错了的地方，如下：
/* HCLK = SYSCLK */
RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1;

/* PCLK2 = HCLK */
RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE2_DIV1;

/* PCLK1 = HCLK */
RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE1_DIV2;
从时钟布局图中可以知道，PCLK1的最大时钟为36MHz,PCLK1怎么能等于HCLK呢？此时的HCLK可是72MHz，从下面代码也可看到，确实2分频嘛，那就是36MHz，肯定是注释错了！本回答被提问者和网友采纳

STM32F0库函数初始化系列：PWM输出

void TIM1_Configuration(void)

  TIM_TimeBaseInitTypeDef TIM_Time1BaseStructure;
  TIM_OCInitTypeDef TIM_OCInitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_TIM1, ENABLE);

  /* Time 定时基础设置*/
  TIM_Time1BaseStructure.TIM_Prescaler = 0;
  TIM_Time1BaseStructure.TIM_CounterMode = TIM_CounterMode_Up;  /* Time 定时设置为上升沿计算模式*/
  TIM_Time1BaseStructure.TIM_Period = (SystemCoreClock / 40000)-1;
  TIM_Time1BaseStructure.TIM_ClockDivision = 0;
  TIM_Time1BaseStructure.TIM_RepetitionCounter = 0;
 
  TIM_TimeBaseInit(TIM1, &TIM_Time1BaseStructure);
 
  /* 频道1，2，3，4的PWM 模式设置 */
  TIM_OCInitStructure.TIM_OCMode = TIM_OCMode_PWM1;
  TIM_OCInitStructure.TIM_OutputState = TIM_OutputState_Enable ;//TIM_OutputState_Enable; //PWM输出使能位
  TIM_OCInitStructure.TIM_OutputNState = TIM_OutputNState_Enable ;//TIM_OutputNState_Enable; //互补PWM输出使能位
  TIM_OCInitStructure.TIM_OCPolarity = TIM_OCPolarity_Low;  //PWM 1为有效电平
  TIM_OCInitStructure.TIM_OCNPolarity = TIM_OCNPolarity_High; //PWM互补 0为有效电平
  TIM_OCInitStructure.TIM_OCIdleState = TIM_OCIdleState_Set;
  TIM_OCInitStructure.TIM_OCNIdleState = TIM_OCIdleState_Reset;
 
  TIM_OCInitStructure.TIM_Pulse = 600-1; //赋占空比值
  TIM_OC2Init(TIM1, &TIM_OCInitStructure);//使能频道2配置
 
  /* TIM1 计算器使能*/
  TIM_Cmd(TIM1, DISABLE);
     
  /* TIM1 主输出使能 */
  TIM_CtrlPWMOutputs(TIM1, DISABLE);