STM32F0xx_StdPeriph_Examples/USART/USART_8xUsartsOneBoard/system_stm32f0xx.c

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/**
  ******************************************************************************
  * @file    system_stm32f0xx.c
  * @author  MCD Application Team
  * @version V1.4.0
  * @date    24-July-2014
  * @brief   CMSIS Cortex-M0 Device Peripheral Access Layer System Source File.
  *          This file contains the system clock configuration for STM32F0xx devices,
  *          and is generated by the clock configuration tool  
  *          STM32F0xx_Clock_Configuration_V1.0.1.xls
  *
  * 1.  This file provides two functions and one global variable to be called from 
  *     user application:
  *      - SystemInit(): Setups the system clock (System clock source, PLL Multiplier
  *                      and Divider factors, AHB/APBx prescalers and Flash settings),
  *                      depending on the configuration made in the clock xls tool.
  *                      This function is called at startup just after reset and 
  *                      before branch to main program. This call is made inside
  *                      the "startup_stm32f0xx.s" file.
  *
  *      - SystemCoreClock variable: Contains the core clock (HCLK), it can be used
  *                                  by the user application to setup the SysTick 
  *                                  timer or configure other parameters.
  *
  *      - SystemCoreClockUpdate(): Updates the variable SystemCoreClock and must
  *                                 be called whenever the core clock is changed
  *                                 during program execution.
  *
  * 2. After each device reset the HSI (8 MHz Range) is used as system clock source.
  *    Then SystemInit() function is called, in "startup_stm32f0xx.s" file, to
  *    configure the system clock before to branch to main program.
  *
  * 3. If the system clock source selected by user fails to startup, the SystemInit()
  *    function will do nothing and HSI still used as system clock source. User can 
  *    add some code to deal with this issue inside the SetSysClock() function.
  *
  * 4. The default value of HSE crystal is set to 8MHz, refer to "HSE_VALUE" define
  *    in "stm32f0xx.h" file. When HSE is used as system clock source, directly or
  *    through PLL, and you are using different crystal you have to adapt the HSE
  *    value to your own configuration.
  *
  * 5. This file configures the system clock as follows:
  *=============================================================================
  *=============================================================================
  *        System Clock source                    | PLL(HSE)
  *-----------------------------------------------------------------------------
  *        SYSCLK(Hz)                             | 48000000
  *-----------------------------------------------------------------------------
  *        HCLK(Hz)                               | 48000000
  *-----------------------------------------------------------------------------
  *        AHB Prescaler                          | 1
  *-----------------------------------------------------------------------------
  *        APB Prescaler                          | 1
  *-----------------------------------------------------------------------------
  *        HSE Frequency(Hz)                      | 8000000
  *----------------------------------------------------------------------------
  *        PLLMUL                                 | 6
  *-----------------------------------------------------------------------------
  *        PREDIV                                 | 1
  *-----------------------------------------------------------------------------
  *        Flash Latency(WS)                      | 1
  *-----------------------------------------------------------------------------
  *        Prefetch Buffer                        | ON
  *-----------------------------------------------------------------------------
  ******************************************************************************
  * @attention
  *
  * <h2><center>&copy; COPYRIGHT 2014 STMicroelectronics</center></h2>
  *
  * Licensed under MCD-ST Liberty SW License Agreement V2, (the "License");
  * You may not use this file except in compliance with the License.
  * You may obtain a copy of the License at:
  *
  *        http://www.st.com/software_license_agreement_liberty_v2
  *
  * Unless required by applicable law or agreed to in writing, software 
  * distributed under the License is distributed on an "AS IS" BASIS, 
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  *
  ******************************************************************************
  */

/** @addtogroup CMSIS
  * @{
  */

/** @addtogroup stm32f0xx_system
  * @{
  */  
  
/** @addtogroup STM32F0xx_System_Private_Includes
  * @{
  */

#include "stm32f0xx.h"

/**
  * @}
  */

/** @addtogroup STM32F0xx_System_Private_TypesDefinitions
  * @{
  */

/**
  * @}
  */

/** @addtogroup STM32F0xx_System_Private_Defines
  * @{
  */
/**
  * @}
  */

/** @addtogroup STM32F0xx_System_Private_Macros
  * @{
  */

/**
  * @}
  */

/** @addtogroup STM32F0xx_System_Private_Variables
  * @{
  */
uint32_t SystemCoreClock    = 48000000;
__I uint8_t AHBPrescTable[16] = {0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 6, 7, 8, 9};

/**
  * @}
  */

/** @addtogroup STM32F0xx_System_Private_FunctionPrototypes
  * @{
  */

static void SetSysClock(void);

/**
  * @}
  */

/** @addtogroup STM32F0xx_System_Private_Functions
  * @{
  */

/**
  * @brief  Setup the microcontroller system.
  *         Initialize the Embedded Flash Interface, the PLL and update the 
  *         SystemCoreClock variable.
  * @param  None
  * @retval None
  */
void SystemInit (void)
{    
  /* Set HSION bit */
  RCC->CR |= (uint32_t)0x00000001;

  /* Reset SW[1:0], HPRE[3:0], PPRE[2:0], ADCPRE and MCOSEL[2:0] bits */
  RCC->CFGR &= (uint32_t)0xF8FFB80C;
  
  /* Reset HSEON, CSSON and PLLON bits */
  RCC->CR &= (uint32_t)0xFEF6FFFF;

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

  /* Reset PLLSRC, PLLXTPRE and PLLMUL[3:0] bits */
  RCC->CFGR &= (uint32_t)0xFFC0FFFF;

  /* Reset PREDIV1[3:0] bits */
  RCC->CFGR2 &= (uint32_t)0xFFFFFFF0;

  /* Reset USARTSW[1:0], I2CSW, CECSW and ADCSW bits */
  RCC->CFGR3 &= (uint32_t)0xFFFFFEAC;

  /* Reset HSI14 bit */
  RCC->CR2 &= (uint32_t)0xFFFFFFFE;

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

  /* Configure the System clock frequency, AHB/APBx prescalers and Flash settings */
  SetSysClock();
}

/**
  * @brief  Update SystemCoreClock according to Clock Register Values
  *         The SystemCoreClock variable contains the core clock (HCLK), it can
  *         be used by the user application to setup the SysTick timer or configure
  *         other parameters.
  *
  * @note   Each time the core clock (HCLK) changes, this function must be called
  *         to update SystemCoreClock variable value. Otherwise, any configuration
  *         based on this variable will be incorrect.         
  *
  * @note   - The system frequency computed by this function is not the real 
  *           frequency in the chip. It is calculated based on the predefined 
  *           constant and the selected clock source:
  *
  *           - If SYSCLK source is HSI, SystemCoreClock will contain the HSI_VALUE(*)
  *                                              
  *           - If SYSCLK source is HSE, SystemCoreClock will contain the HSE_VALUE(**)
  *                          
  *           - If SYSCLK source is PLL, SystemCoreClock will contain the HSE_VALUE(**)
  *             or HSI_VALUE(*) multiplied/divided by the PLL factors.
  *
  *         (*) HSI_VALUE is a constant defined in stm32f0xx.h file (default value
  *             8 MHz) but the real value may vary depending on the variations
  *             in voltage and temperature.
  *
  *         (**) HSE_VALUE is a constant defined in stm32f0xx.h file (default value
  *              8 MHz), user has to ensure that HSE_VALUE is same as the real
  *              frequency of the crystal used. Otherwise, this function may
  *              have wrong result.
  *
  *         - The result of this function could be not correct when using fractional
  *           value for HSE crystal.
  * @param  None
  * @retval None
  */
void SystemCoreClockUpdate (void)
{
  uint32_t tmp = 0, pllmull = 0, pllsource = 0, prediv1factor = 0;

  /* Get SYSCLK source -------------------------------------------------------*/
  tmp = RCC->CFGR & RCC_CFGR_SWS;
  
  switch (tmp)
  {
    case 0x00:  /* HSI used as system clock */
      SystemCoreClock = HSI_VALUE;
      break;
    case 0x04:  /* HSE used as system clock */
      SystemCoreClock = HSE_VALUE;
      break;
    case 0x08:  /* PLL used as system clock */
      /* Get PLL clock source and multiplication factor ----------------------*/
      pllmull = RCC->CFGR & RCC_CFGR_PLLMULL;
      pllsource = RCC->CFGR & RCC_CFGR_PLLSRC;
      pllmull = ( pllmull >> 18) + 2;
      
      if (pllsource == 0x00)
      {
        /* HSI oscillator clock divided by 2 selected as PLL clock entry */
        SystemCoreClock = (HSI_VALUE >> 1) * pllmull;
      }
      else
      {
        prediv1factor = (RCC->CFGR2 & RCC_CFGR2_PREDIV1) + 1;
        /* HSE oscillator clock selected as PREDIV1 clock entry */
        SystemCoreClock = (HSE_VALUE / prediv1factor) * pllmull; 
      }      
      break;
    default: /* HSI used as system clock */
      SystemCoreClock = HSI_VALUE;
      break;
  }
  /* Compute HCLK clock frequency ----------------*/
  /* Get HCLK prescaler */
  tmp = AHBPrescTable[((RCC->CFGR & RCC_CFGR_HPRE) >> 4)];
  /* HCLK clock frequency */
  SystemCoreClock >>= tmp;  
}

/**
  * @brief  Configures the System clock frequency, AHB/APBx prescalers and Flash
  *         settings.
  * @note   This function should be called only once the RCC clock configuration
  *         is reset to the default reset state (done in SystemInit() function).
  * @param  None
  * @retval None
  */
static void SetSysClock(void)
{
  __IO uint32_t StartUpCounter = 0, HSEStatus = 0;

/******************************************************************************/
/*            PLL (clocked by HSE) used as System clock source                */
/******************************************************************************/
  
  /* SYSCLK, HCLK, PCLK configuration ----------------------------------------*/
  /* Enable HSE */    
  RCC->CR |= ((uint32_t)RCC_CR_HSEON);
 
  /* Wait till HSE is ready and if Time out is reached exit */
  do
  {
    HSEStatus = RCC->CR & RCC_CR_HSERDY;
    StartUpCounter++;  
  } while((HSEStatus == 0) && (StartUpCounter != HSE_STARTUP_TIMEOUT));

  if ((RCC->CR & RCC_CR_HSERDY) != RESET)
  {
    HSEStatus = (uint32_t)0x01;
  }
  else
  {
    HSEStatus = (uint32_t)0x00;
  }  

  if (HSEStatus == (uint32_t)0x01)
  {
    /* Enable Prefetch Buffer and set Flash Latency */
    FLASH->ACR = FLASH_ACR_PRFTBE | FLASH_ACR_LATENCY;
 
    /* HCLK = SYSCLK */
    RCC->CFGR |= (uint32_t)RCC_CFGR_HPRE_DIV1;
      
    /* PCLK = HCLK */
    RCC->CFGR |= (uint32_t)RCC_CFGR_PPRE_DIV1;

    /* PLL configuration */
    RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLXTPRE | RCC_CFGR_PLLMULL));
    RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_PREDIV1 | RCC_CFGR_PLLXTPRE_PREDIV1 | RCC_CFGR_PLLMULL6);
            
    /* Enable PLL */
    RCC->CR |= RCC_CR_PLLON;

    /* Wait till PLL is ready */
    while((RCC->CR & RCC_CR_PLLRDY) == 0)
    {
    }

    /* Select PLL as system clock source */
    RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));
    RCC->CFGR |= (uint32_t)RCC_CFGR_SW_PLL;    

    /* Wait till PLL is used as system clock source */
    while ((RCC->CFGR & (uint32_t)RCC_CFGR_SWS) != (uint32_t)RCC_CFGR_SWS_PLL)
    {
    }
  }
  else
  { /* If HSE fails to start-up, the application will have wrong clock 
         configuration. User can add here some code to deal with this error */
  }  
}

/**
  * @}
  */

/**
  * @}
  */

/**
  * @}
  */

/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/