/**
  ******************************************************************************
  * @file    system_stm32f0xx.c
  * @author  MCD Application Team
  * @version V1.0.0
  * @date    17-January-2014
  * @brief   CMSIS Cortex-M0 Device Peripheral Access Layer System Source File.
  *          This file contains the system clock configuration for STM32F0xx devices,
  *          and  is customized for use with STM32F072B-DISCOVERY Kit.
  *
  *
  *          The STM32F072x is configured to run at 48 MHz, following the five
  *          configuration below:
  *            - SOURCE_HSI48 (default)        : HSI48 (48MHz) used as system clock source.
  *            - PLL_SOURCE_HSI                : HSI (~8MHz) used to clock the PLL, and
  *                                              the PLL is used as system clock source.
  *            - PLL_SOURCE_HSI48              : HSI48 (48MHz) used to clock the PLL, and
  *                                              the PLL is used as system clock source.
  *            - PLL_SOURCE_HSE                : HSE (8MHz) used to clock the PLL, and
  *                                              the PLL is used as system clock source.
  *            - PLL_SOURCE_HSE_BYPASS         : HSE bypassed with an external clock
  *                                              (8MHz, coming from ST-Link) used to clock
  *                                              the PLL, and the PLL is used as system
  *                                              clock source.
  *
  *
  * 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.
  *
  ******************************************************************************
  * @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
  * @{
  */
/**
  * @}
  */

/*!< Uncomment the following line if you need to relocate your vector Table in
     Internal SRAM. */
/* #define VECT_TAB_SRAM */
#define VECT_TAB_OFFSET  0x0 /*!< Vector Table base offset field.
                                  This value must be a multiple of 0x200. */

/* Select the PLL clock source */

//#define SOURCE_HSI48
//#define PLL_SOURCE_HSI48       /* HSI48 (48MHz) used to clock USB, system clock and the PLL*/
//#define PLL_SOURCE_HSI        /* HSI (~8MHz) used to clock the PLL, and the PLL is used as system clock source*/
#define PLL_SOURCE_HSE        /* HSE (8MHz) used to clock the PLL, and the PLL is used as system clock source */
//#define PLL_SOURCE_HSE_BYPASS   /* HSE bypassed with an external clock (8MHz, coming from ST-Link) used to clock
//                                   the PLL, and the PLL is used as system clock source */


/** @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[3:0] bits MCOPRE[2:0] */
  RCC->CFGR &= (uint32_t)0x80FFB80C;

  /* 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)0xFFC07FFF;

  /* 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 & HSI48 bit */
  RCC->CR2 &= (uint32_t)0xFFFEFFFE;

  /* 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.
  * @note     - If SYSCLK source is HSI48, function returns constant HSI48_VALUE(***)
  *
  *         (*) 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.
  * @note  (***) HSI48_VALUE is a constant defined in stm32f0xx.h file (default value
  *              48 MHz) but the real value may vary depending on the variations
  *              in voltage and temperature.
  *
  *         - 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;
  case 0x0C:  /* HSI48 used as system clock */
    SystemCoreClock = HSI48_VALUE;
    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;

  /* SYSCLK, HCLK, PCLK configuration ----------------------------------------*/
    /* At this stage the HSI is already enabled */

    /* 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;

#ifndef SOURCE_HSI48

 #if defined (PLL_SOURCE_HSI)
    /* PLL configuration = HSI * 6 = 48 MHz */
    RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLXTPRE | RCC_CFGR_PLLMULL));
    RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_HSI_PREDIV | RCC_CFGR_PLLXTPRE_PREDIV1 | RCC_CFGR_PLLMULL6);
 #elif defined (PLL_SOURCE_HSI48)
   /* Enable HSI48 */
    RCC->CR2 |= RCC_CR2_HSI48ON;
    /* PLL configuration = HSI48 * 1 = 48 MHz */
    RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_PLLSRC | RCC_CFGR_PLLXTPRE | RCC_CFGR_PLLMULL));
    RCC->CFGR |= (uint32_t)(RCC_CFGR_PLLSRC_HSI48_PREDIV | RCC_CFGR_PLLXTPRE_PREDIV1_Div2);

 #else
   /* Enable HSE */
   RCC->CR |= ((uint32_t)RCC_CR_HSEON);
   #if defined (PLL_SOURCE_HSE_BYPASS)
    /* HSE oscillator bypassed with external clock */
    RCC->CR |= (uint32_t)(RCC_CR_HSEBYP);
   #endif
   /* 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)
  {
    /* PLL configuration = HSE * 6 = 48 MHz */
    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);

  }
  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 */
  }



 #endif /* PLL_SOURCE_HSI */
    /* 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
   /* Enable HSI48 */
    RCC->CR2 |= RCC_CR2_HSI48ON;
  /* Wait till HSI48RDY is set */
    while((RCC->CR2 & RCC_CR2_HSI48RDY) == 0)
    { }
  /* Select HSI48 as system clock source */
    RCC->CFGR &= (uint32_t)((uint32_t)~(RCC_CFGR_SW));
    RCC->CFGR |= (uint32_t)RCC_CFGR_SW_HSI48;

#endif

}

/**
  * @}
  */

/**
  * @}
  */

/**
  * @}
  */

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