[STM32F4 ] PLL 설정

[STM32F4 ] PLL 설정

STM32F4xx_Clock_Configuration_V1.1.0.xls

STM32F4 의 최대 동작 속도는 168Mhz이다.  SystemInit() 함수를 이용하여 PLL을 설정 가능하고 startup_stm32f4xx.s 에서 초기화시 실행된다.

외부 입력 클럭은 8Mhz로 설정했다.

#if !defined  (HSE_VALUE) 
  #define HSE_VALUE    ((uint32_t)8000000) /*!< Value of the External oscillator in Hz */    
#endif /* HSE_VALUE */


/* PLL_VCO = (HSE_VALUE or HSI_VALUE / PLL_M) * PLL_N */
#define PLL_M      8

void SystemInit(void)
{
  /* FPU settings ------------------------------------------------------------*/
  #if (__FPU_PRESENT == 1) && (__FPU_USED == 1)
    SCB->CPACR |= ((3UL << 10*2)|(3UL << 11*2));  /* set CP10 and CP11 Full Access */
  #endif

  /* Reset the RCC clock configuration to the default reset state ------------*/
  /* Set HSION bit */
  RCC->CR |= (uint32_t)0x00000001;

  /* Reset CFGR register */
  RCC->CFGR = 0x00000000;

  /* Reset HSEON, CSSON and PLLON bits */
  RCC->CR &= (uint32_t)0xFEF6FFFF;

  /* Reset PLLCFGR register */
  RCC->PLLCFGR = 0x24003010;

  /* Reset HSEBYP bit */
  RCC->CR &= (uint32_t)0xFFFBFFFF;

  /* Disable all interrupts */
  RCC->CIR = 0x00000000;

#ifdef DATA_IN_ExtSRAM
  SystemInit_ExtMemCtl();
#endif /* DATA_IN_ExtSRAM */
        
  /* Configure the System clock source, PLL Multiplier and Divider factors,
     AHB/APBx prescalers and Flash settings ----------------------------------*/
  SetSysClock();

  /* Configure the Vector Table location add offset address ------------------*/
#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
}

PA8에 PCU클럭을 출력해서 확인 할 수 있는데. 아래와 같이 설정해 주면 된다.

  /* Output HSE clock on MCO1 pin(PA8) ****************************************/
  /* Enable the GPIOA peripheral */
  RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);
 
  /* Configure MCO1 pin(PA8) in alternate function */
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_8;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_100MHz;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP; 
  GPIO_Init(GPIOA, &GPIO_InitStructure);
   
  /* HSE clock selected to output on MCO1 pin(PA8)*/
  RCC_MCO1Config(RCC_MCO1Source_PLLCLK, RCC_MCO1Div_1);

STM32F4 RCC블록도