/**
  ******************************************************************************
  * @file    system_stm32g0xx.c
  * @author  MCD Application Team
  * @brief   CMSIS Cortex-M0+ Device Peripheral Access Layer System Source File
  *
  *   This file provides two functions and one global variable to be called from
  *   user application:
  *      - SystemInit(): This function is called at startup just after reset and
  *                      before branch to main program. This call is made inside
  *                      the "startup_stm32g0xx.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.
  *
  *   After each device reset the HSI (8 MHz then 16 MHz) is used as system clock source.
  *   Then SystemInit() function is called, in "startup_stm32g0xx.s" file, to
  *   configure the system clock before to branch to main program.
  *
  *   This file configures the system clock as follows:
  *=============================================================================
  *-----------------------------------------------------------------------------
  *        System Clock source                    | HSI
  *-----------------------------------------------------------------------------
  *        SYSCLK(Hz)                             | 16000000
  *-----------------------------------------------------------------------------
  *        HCLK(Hz)                               | 16000000
  *-----------------------------------------------------------------------------
  *        AHB Prescaler                          | 1
  *-----------------------------------------------------------------------------
  *        APB Prescaler                          | 1
  *-----------------------------------------------------------------------------
  *        HSI Division factor                    | 1
  *-----------------------------------------------------------------------------
  *        PLL_M                                  | 1
  *-----------------------------------------------------------------------------
  *        PLL_N                                  | 8
  *-----------------------------------------------------------------------------
  *        PLL_P                                  | 7
  *-----------------------------------------------------------------------------
  *        PLL_Q                                  | 2
  *-----------------------------------------------------------------------------
  *        PLL_R                                  | 2
  *-----------------------------------------------------------------------------
  *        Require 48MHz for RNG                  | Disabled
  *-----------------------------------------------------------------------------
  *=============================================================================
  ******************************************************************************
  * @attention
  *
  * Copyright (c) 2018-2021 STMicroelectronics.
  * All rights reserved.
  *
  * This software is licensed under terms that can be found in the LICENSE file
  * in the root directory of this software component.
  * If no LICENSE file comes with this software, it is provided AS-IS.
  *
  ******************************************************************************
  */
/** @addtogroup CMSIS
  * @{
  */

/** @addtogroup stm32g0xx_system
  * @{
  */

/** @addtogroup STM32G0xx_System_Private_Includes
  * @{
  */

#include "stm32g0xx.h"

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

#if !defined  (HSI_VALUE)
  #define HSI_VALUE  (16000000UL)   /*!< Value of the Internal oscillator in Hz*/
#endif /* HSI_VALUE */

#if !defined  (LSI_VALUE)
 #define LSI_VALUE   (32000UL)     /*!< Value of LSI in Hz*/
#endif /* LSI_VALUE */

#if !defined  (LSE_VALUE)
  #define LSE_VALUE  (32768UL)      /*!< Value of LSE in Hz*/
#endif /* LSE_VALUE */

/**
  * @}
  */

/** @addtogroup STM32G0xx_System_Private_TypesDefinitions
  * @{
  */

/**
  * @}
  */

/** @addtogroup STM32G0xx_System_Private_Defines
  * @{
  */

/************************* Miscellaneous Configuration ************************/
/* Note: Following vector table addresses must be defined in line with linker
         configuration. */
/*!< Uncomment the following line if you need to relocate the vector table
     anywhere in Flash or Sram, else the vector table is kept at the automatic
     remap of boot address selected */
/* #define USER_VECT_TAB_ADDRESS */

#if defined(USER_VECT_TAB_ADDRESS)
/*!< Uncomment the following line if you need to relocate your vector Table
     in Sram else user remap will be done in Flash. */
/* #define VECT_TAB_SRAM */
#if defined(VECT_TAB_SRAM)
#define VECT_TAB_BASE_ADDRESS   SRAM_BASE       /*!< Vector Table base address field.
                                                     This value must be a multiple of 0x200. */
#else
#define VECT_TAB_BASE_ADDRESS   FLASH_BASE      /*!< Vector Table base address field.
                                                     This value must be a multiple of 0x200. */
#endif /* VECT_TAB_SRAM */

#if !defined(VECT_TAB_OFFSET)
#define VECT_TAB_OFFSET         0x00000000U     /*!< Vector Table offset field.
                                                     This value must be a multiple of 0x200. */
#endif /* VECT_TAB_OFFSET */

#endif /* USER_VECT_TAB_ADDRESS */
/******************************************************************************/
/**
  * @}
  */

/** @addtogroup STM32G0xx_System_Private_Macros
  * @{
  */

/**
  * @}
  */

/** @addtogroup STM32G0xx_System_Private_Variables
  * @{
  */
  /* The SystemCoreClock variable is updated in three ways:
      1) by calling CMSIS function SystemCoreClockUpdate()
      2) by calling HAL API function HAL_RCC_GetHCLKFreq()
      3) each time HAL_RCC_ClockConfig() is called to configure the system clock frequency
         Note: If you use this function to configure the system clock; then there
               is no need to call the 2 first functions listed above, since SystemCoreClock
               variable is updated automatically.
  */
  uint32_t SystemCoreClock = 16000000UL;

  const uint32_t AHBPrescTable[16UL] = {0UL, 0UL, 0UL, 0UL, 0UL, 0UL, 0UL, 0UL, 1UL, 2UL, 3UL, 4UL, 6UL, 7UL, 8UL, 9UL};
  const uint32_t APBPrescTable[8UL] =  {0UL, 0UL, 0UL, 0UL, 1UL, 2UL, 3UL, 4UL};

/**
  * @}
  */

/** @addtogroup STM32G0xx_System_Private_FunctionPrototypes
  * @{
  */

/**
  * @}
  */

/** @addtogroup STM32G0xx_System_Private_Functions
  * @{
  */

/**
  * @brief  Setup the microcontroller system.
  * @param  None
  * @retval None
  */
void SystemInit(void)
{
  /* Configure the Vector Table location -------------------------------------*/
#if defined(USER_VECT_TAB_ADDRESS)
  SCB->VTOR = VECT_TAB_BASE_ADDRESS | VECT_TAB_OFFSET; /* Vector Table Relocation */
#endif /* USER_VECT_TAB_ADDRESS */
}

/**
  * @brief  Update SystemCoreClock variable 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(**) / HSI division factor
  *
  *           - If SYSCLK source is HSE, SystemCoreClock will contain the HSE_VALUE(***)
  *
  *           - If SYSCLK source is LSI, SystemCoreClock will contain the LSI_VALUE
  *
  *           - If SYSCLK source is LSE, SystemCoreClock will contain the LSE_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 stm32g0xx_hal_conf.h file (default value
  *              16 MHz) but the real value may vary depending on the variations
  *              in voltage and temperature.
  *
  *         (***) HSE_VALUE is a constant defined in stm32g0xx_hal_conf.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;
  uint32_t pllvco;
  uint32_t pllr;
  uint32_t pllsource;
  uint32_t pllm;
  uint32_t hsidiv;

  /* Get SYSCLK source -------------------------------------------------------*/
  switch (RCC->CFGR & RCC_CFGR_SWS)
  {
    case RCC_CFGR_SWS_0:                /* HSE used as system clock */
      SystemCoreClock = HSE_VALUE;
      break;

    case (RCC_CFGR_SWS_1 | RCC_CFGR_SWS_0):  /* LSI used as system clock */
      SystemCoreClock = LSI_VALUE;
      break;

    case RCC_CFGR_SWS_2:                /* LSE used as system clock */
      SystemCoreClock = LSE_VALUE;
      break;

    case RCC_CFGR_SWS_1:  /* PLL used as system clock */
      /* PLL_VCO = (HSE_VALUE or HSI_VALUE / PLLM) * PLLN
         SYSCLK = PLL_VCO / PLLR
         */
      pllsource = (RCC->PLLCFGR & RCC_PLLCFGR_PLLSRC);
      pllm = ((RCC->PLLCFGR & RCC_PLLCFGR_PLLM) >> RCC_PLLCFGR_PLLM_Pos) + 1UL;

      if(pllsource == 0x03UL)           /* HSE used as PLL clock source */
      {
        pllvco = (HSE_VALUE / pllm);
      }
      else                              /* HSI used as PLL clock source */
      {
          pllvco = (HSI_VALUE / pllm);
      }
      pllvco = pllvco * ((RCC->PLLCFGR & RCC_PLLCFGR_PLLN) >> RCC_PLLCFGR_PLLN_Pos);
      pllr = (((RCC->PLLCFGR & RCC_PLLCFGR_PLLR) >> RCC_PLLCFGR_PLLR_Pos) + 1UL);

      SystemCoreClock = pllvco/pllr;
      break;
      
    case 0x00000000U:                   /* HSI used as system clock */
    default:                            /* HSI used as system clock */
      hsidiv = (1UL << ((READ_BIT(RCC->CR, RCC_CR_HSIDIV))>> RCC_CR_HSIDIV_Pos));
      SystemCoreClock = (HSI_VALUE/hsidiv);
      break;
  }
  /* Compute HCLK clock frequency --------------------------------------------*/
  /* Get HCLK prescaler */
  tmp = AHBPrescTable[((RCC->CFGR & RCC_CFGR_HPRE) >> RCC_CFGR_HPRE_Pos)];
  /* HCLK clock frequency */
  SystemCoreClock >>= tmp;
}


/**
  * @}
  */

/**
  * @}
  */

/**
  * @}
  */
