stm32时钟设置函数

Posted 2020-08-09 prayer521

这里涉及到一个很重要的寄存器，时钟配置寄存器：RCC_CFGR

 1 #if defined (STM32F10X_LD_VL) || (defined STM32F10X_MD_VL) || (defined STM32F10X_HD_VL)
 2 /* #define SYSCLK_FREQ_HSE    HSE_VALUE */
 3  #define SYSCLK_FREQ_24MHz  24000000
 4 #else
 5 /* #define SYSCLK_FREQ_HSE    HSE_VALUE */
 6 /* #define SYSCLK_FREQ_24MHz  24000000 */ 
 7 /* #define SYSCLK_FREQ_36MHz  36000000 */
 8 /* #define SYSCLK_FREQ_48MHz  48000000 */
 9 /* #define SYSCLK_FREQ_56MHz  56000000 */
10 #define SYSCLK_FREQ_72MHz  72000000
11 #endif

 1 /**
 2   * @brief  Setup the microcontroller system
 3   *         Initialize the Embedded Flash Interface, the PLL and update the 
 4   *         SystemCoreClock variable.
 5   * @note   This function should be used only after reset.
 6   * @param  None
 7   * @retval None
 8   */
 9 void SystemInit (void)
10 {
11   /* Reset the RCC clock configuration to the default reset state(for debug purpose) */
12   /* Set HSION bit */
13   RCC->CR |= (uint32_t)0x00000001;
14 
15   /* Reset SW, HPRE, PPRE1, PPRE2, ADCPRE and MCO bits */
16 #ifndef STM32F10X_CL
17   RCC->CFGR &= (uint32_t)0xF8FF0000;
18 #else
19   RCC->CFGR &= (uint32_t)0xF0FF0000;
20 #endif /* STM32F10X_CL */   
21   
22   /* Reset HSEON, CSSON and PLLON bits */
23   RCC->CR &= (uint32_t)0xFEF6FFFF;
24 
25   /* Reset HSEBYP bit */
26   RCC->CR &= (uint32_t)0xFFFBFFFF;
27 
28   /* Reset PLLSRC, PLLXTPRE, PLLMUL and USBPRE/OTGFSPRE bits */
29   RCC->CFGR &= (uint32_t)0xFF80FFFF;
30 
31 #ifdef STM32F10X_CL
32   /* Reset PLL2ON and PLL3ON bits */
33   RCC->CR &= (uint32_t)0xEBFFFFFF;
34 
35   /* Disable all interrupts and clear pending bits  */
36   RCC->CIR = 0x00FF0000;
37 
38   /* Reset CFGR2 register */
39   RCC->CFGR2 = 0x00000000;
40 #elif defined (STM32F10X_LD_VL) || defined (STM32F10X_MD_VL) || (defined STM32F10X_HD_VL)
41   /* Disable all interrupts and clear pending bits  */
42   RCC->CIR = 0x009F0000;
43 
44   /* Reset CFGR2 register */
45   RCC->CFGR2 = 0x00000000;      
46 #else
47   /* Disable all interrupts and clear pending bits  */
48   RCC->CIR = 0x009F0000;
49 #endif /* STM32F10X_CL */
50     
51 #if defined (STM32F10X_HD) || (defined STM32F10X_XL) || (defined STM32F10X_HD_VL)
52   #ifdef DATA_IN_ExtSRAM
53     SystemInit_ExtMemCtl(); 
54   #endif /* DATA_IN_ExtSRAM */
55 #endif 
56 
57   /* Configure the System clock frequency, HCLK, PCLK2 and PCLK1 prescalers */
58   /* Configure the Flash Latency cycles and enable prefetch buffer */
59   SetSysClock();
60 
61 #ifdef VECT_TAB_SRAM
62   SCB->VTOR = SRAM_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal SRAM. */
63 #else
64   SCB->VTOR = FLASH_BASE | VECT_TAB_OFFSET; /* Vector Table Relocation in Internal FLASH. */
65 #endif 
66 }

 

/**
  * @brief  Configures the System clock frequency, HCLK, PCLK2 and PCLK1 prescalers.
  * @param  None
  * @retval None
  */
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

 

  1 /**
  2   * @brief  Sets System clock frequency to 72MHz and configure HCLK, PCLK2 
  3   *         and PCLK1 prescalers. 
  4   * @note   This function should be used only after reset.
  5   * @param  None
  6   * @retval None
  7   */
  8 static void SetSysClockTo72(void)
  9 {
 10   __IO uint32_t StartUpCounter = 0, HSEStatus = 0;
 11   
 12   /* SYSCLK, HCLK, PCLK2 and PCLK1 configuration ---------------------------*/    
 13   /* Enable HSE */    
 14   RCC->CR |= ((uint32_t)RCC_CR_HSEON);
 15  
 16   /* Wait till HSE is ready and if Time out is reached exit */
 17   do
 18   {
 19     HSEStatus = RCC->CR & RCC_CR_HSERDY;
 20     StartUpCounter++;  
 21   } while((HSEStatus == 0) && (StartUpCounter != HSE_STARTUP_TIMEOUT));
 22 
 23   if ((RCC->CR & RCC_CR_HSERDY) != RESET)
 24   {
 25     HSEStatus = (uint32_t)0x01;
 26   }
 27   else
 28   {
 29     HSEStatus = (uint32_t)0x00;
 30   }  
 31 
 32   if (HSEStatus == (uint32_t)0x01)
 33   {
 34     /* Enable Prefetch Buffer */
 35     FLASH->ACR |= FLASH_ACR_PRFTBE;
 36 
 37     /* Flash 2 wait state */
 38     FLASH->ACR &= (uint32_t)((uint32_t)~FLASH_ACR_LATENCY);
 39     FLASH->ACR |= (uint32_t)FLASH_ACR_LATENCY_2;    
 40 
 41  
 42     /* HCLK = SYSCLK */
 43     RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1;
 44       
 45     /* PCLK2 = HCLK */
 46     RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE2_DIV1;
 47     
 48     /* PCLK1 = HCLK */
 49     RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE1_DIV2;
 50 
 51 #ifdef STM32F10X_CL
 52     /* Configure PLLs ------------------------------------------------------*/
 53     /* PLL2 configuration: PLL2CLK = (HSE / 5) * 8 = 40 MHz */
 54     /* PREDIV1 configuration: PREDIV1CLK = PLL2 / 5 = 8 MHz */
 55         
 56     RCC->CFGR2 &= (uint32_t)~(RCC_CFGR2_PREDIV2 | RCC_CFGR2_PLL2MUL |
 57                               RCC_CFGR2_PREDIV1 | RCC_CFGR2_PREDIV1SRC);
 58     RCC->CFGR2 |= (uint32_t)(RCC_CFGR2_PREDIV2_DIV5 | RCC_CFGR2_PLL2MUL8 |
 59                              RCC_CFGR2_PREDIV1SRC_PLL2 | RCC_CFGR2_PREDIV1_DIV5);
 60   
 61     /* Enable PLL2 */
 62     RCC->CR |= RCC_CR_PLL2ON;
 63     /* Wait till PLL2 is ready */
 64     while((RCC->CR & RCC_CR_PLL2RDY) == 0)
 65     {
 66     }
 67     
 68    
 69     /* PLL configuration: PLLCLK = PREDIV1 * 9 = 72 MHz */ 
 70     RCC->CFGR &= (uint32_t)~(RCC_CFGR_PLLXTPRE | RCC_CFGR_PLLSRC | RCC_CFGR_PLLMULL);
 71     RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLXTPRE_PREDIV1 | RCC_CFGR_PLLSRC_PREDIV1 | 
 72                             RCC_CFGR_PLLMULL9); 
 73 #else    
 74     /*  PLL configuration: PLLCLK = HSE * 9 = 72 MHz */
 75     RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLXTPRE |
 76                                         RCC_CFGR_PLLMULL));
 77     RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_HSE | RCC_CFGR_PLLMULL9);
 78 #endif /* STM32F10X_CL */
 79 
 80     /* Enable PLL */
 81     RCC->CR |= RCC_CR_PLLON;
 82 
 83     /* Wait till PLL is ready */
 84     while((RCC->CR & RCC_CR_PLLRDY) == 0)
 85     {
 86     }
 87     
 88     /* Select PLL as system clock source */
 89     RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));
 90     RCC->CFGR |= (uint32_t)RCC_CFGR_SW_PLL;    
 91 
 92     /* Wait till PLL is used as system clock source */
 93     while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS) != (uint32_t)0x08)
 94     {
 95     }
 96   }
 97   else
 98   { /* If HSE fails to start-up, the application will have wrong clock 
 99          configuration. User can add here some code to deal with this error */
100   }
101 }