text: /***************************************************************************//**
   * @file em_burtc.c
   * @brief Backup Real Time Counter (BURTC) Peripheral API
   * @version 5.1.2
   *******************************************************************************
   * @section License
   * <b>Copyright 2016 Silicon Laboratories, Inc. http://www.silabs.com</b>
   *******************************************************************************
   *
   * Permission is granted to anyone to use this software for any purpose,
   * including commercial applications, and to alter it and redistribute it
   * freely, subject to the following restrictions:
   *
   * 1. The origin of this software must not be misrepresented; you must not
   *    claim that you wrote the original software.
   * 2. Altered source versions must be plainly marked as such, and must not be
   *    misrepresented as being the original software.
   * 3. This notice may not be removed or altered from any source distribution.
   *
   * DISCLAIMER OF WARRANTY/LIMITATION OF REMEDIES: Silicon Labs has no
   * obligation to support this Software. Silicon Labs is providing the
   * Software "AS IS", with no express or implied warranties of any kind,
   * including, but not limited to, any implied warranties of merchantability
   * or fitness for any particular purpose or warranties against infringement
   * of any proprietary rights of a third party.
   *
   * Silicon Labs will not be liable for any consequential, incidental, or
   * special damages, or any other relief, or for any claim by any third party,
   * arising from your use of this Software.
   *
   ******************************************************************************/
  
  
  #include "em_burtc.h"
  #if defined(BURTC_PRESENT)
  
  /***************************************************************************//**
   * @addtogroup emlib
   * @{
   ******************************************************************************/
  
  /***************************************************************************//**
   * @addtogroup BURTC
   * @brief Backup Real Time Counter (BURTC) Peripheral API
   * @details
   *  This module contains functions to control the BURTC peripheral of Silicon
   *  Labs 32-bit MCUs. The Backup Real Time Counter allows timekeeping in all
   *  energy modes. The Backup RTC is also available when the system is in backup
   *  mode.
   * @{
   ******************************************************************************/
  
  /*******************************************************************************
   *******************************   DEFINES   ***********************************
   ******************************************************************************/
  
  /*******************************************************************************
   **************************   LOCAL FUNCTIONS   ********************************
   ******************************************************************************/
  
  /** @cond DO_NOT_INCLUDE_WITH_DOXYGEN */
  /***************************************************************************//**
   * @brief Convert dividend to prescaler logarithmic value. Only works for even
   *        numbers equal to 2^n
   * @param[in] div Unscaled dividend,
   * @return Base 2 logarithm of input, as used by fixed prescalers
   ******************************************************************************/
  __STATIC_INLINE uint32_t divToLog2(uint32_t div)
  {
    uint32_t log2;
  
    /* Prescaler accepts an argument of 128 or less, valid values being 2^n */
    EFM_ASSERT((div > 0) && (div <= 32768));
  
    /* Count leading zeroes and "reverse" result, Cortex-M3 intrinsic */
    log2 = (31 - __CLZ(div));
  
    return log2;
  }
  
  
  /***************************************************************************//**
   * @brief
   *   Wait for ongoing sync of register(s) to low frequency domain to complete.
   *
   * @param[in] mask
   *   Bitmask corresponding to SYNCBUSY register defined bits, indicating
   *   registers that must complete any ongoing synchronization.
   ******************************************************************************/
  __STATIC_INLINE void regSync(uint32_t mask)
  {
    /* Avoid deadlock if modifying the same register twice when freeze mode is
       activated, or when no clock is selected for the BURTC. If no clock is
       selected, then the sync is done once the clock source is set. */
    if ((BURTC->FREEZE & BURTC_FREEZE_REGFREEZE)
        || ((BURTC->CTRL & _BURTC_CTRL_CLKSEL_MASK) == BURTC_CTRL_CLKSEL_NONE))
    {
      return;
    }
    /* Wait for any pending previous write operation to have been completed */
    /* in low frequency domain. This is only required for the Gecko Family */
    while (BURTC->SYNCBUSY & mask)
      ;
  }
  /** @endcond */
  
  
  /*******************************************************************************
   **************************   GLOBAL FUNCTIONS   *******************************
   ******************************************************************************/
  
  /***************************************************************************//**
   * @brief Initialize BURTC
   *
   * @details
   *    Configures the BURTC peripheral.
   *
   * @note
   *   Before initialization, BURTC module must first be enabled by clearing the
   *   reset bit in the RMU, i.e.
   * @verbatim
   *   RMU_ResetControl(rmuResetBU, rmuResetModeClear);
   * @endverbatim
   *   Compare channel 0 must be configured outside this function, before
   *   initialization if enable is set to true. The counter will always be reset.
   *
   * @param[in] burtcInit
   *   Pointer to BURTC initialization structure
   ******************************************************************************/
  void BURTC_Init(const BURTC_Init_TypeDef *burtcInit)
  {
    uint32_t ctrl;
    uint32_t presc;
  
    /* Check initializer structure integrity */
    EFM_ASSERT(burtcInit != (BURTC_Init_TypeDef *) 0);
    /* Clock divider must be between 1 and 128, really on the form 2^n */
    EFM_ASSERT((burtcInit->clkDiv >= 1) && (burtcInit->clkDiv <= 128));
    /* Ignored compare bits during low power operation must be less than 7 */
    /* Note! Giant Gecko revision C errata, do NOT use LPCOMP=7 */
    EFM_ASSERT(burtcInit->lowPowerComp <= 6);
    /* You cannot enable the BURTC if mode is set to disabled */
    EFM_ASSERT((burtcInit->enable == false) ||
               ((burtcInit->enable == true)
                && (burtcInit->mode != burtcModeDisable)));
    /* Low power mode is only available with LFRCO or LFXO as clock source */
    EFM_ASSERT((burtcInit->clkSel != burtcClkSelULFRCO)
               || ((burtcInit->clkSel == burtcClkSelULFRCO)
                    && (burtcInit->lowPowerMode == burtcLPDisable)));
  
    /* Calculate prescaler value from clock divider input */
    /* Note! If clock select (clkSel) is ULFRCO, a clock divisor (clkDiv) of
       value 1 will select a 2kHz ULFRCO clock, while any other value will
       select a 1kHz ULFRCO clock source. */
    presc = divToLog2(burtcInit->clkDiv);
  
    /* Make sure all registers are updated simultaneously */
    if (burtcInit->enable)
    {
      BURTC_FreezeEnable(true);
    }
  
    /* Modification of LPMODE register requires sync with potential ongoing
     * register updates in LF domain. */
    regSync(BURTC_SYNCBUSY_LPMODE);
  
    /* Configure low power mode */
    BURTC->LPMODE = (uint32_t) (burtcInit->lowPowerMode);
  
    /* New configuration */
    ctrl = (BURTC_CTRL_RSTEN
            | (burtcInit->mode)
            | (burtcInit->debugRun << _BURTC_CTRL_DEBUGRUN_SHIFT)
            | (burtcInit->compare0Top << _BURTC_CTRL_COMP0TOP_SHIFT)
            | (burtcInit->lowPowerComp << _BURTC_CTRL_LPCOMP_SHIFT)
            | (presc << _BURTC_CTRL_PRESC_SHIFT)
            | (burtcInit->clkSel)
            | (burtcInit->timeStamp << _BURTC_CTRL_BUMODETSEN_SHIFT));
  
    /* Clear interrupts */
    BURTC_IntClear(0xFFFFFFFF);
  
    /* Set new configuration */
    BURTC->CTRL = ctrl;
  
    /* Enable BURTC and counter */
    if (burtcInit->enable)
    {
      /* To enable BURTC counter, we need to disable reset */
      BURTC_Enable(true);
  
      /* Clear freeze */
      BURTC_FreezeEnable(false);
    }
  }
  
  
  /***************************************************************************//**
   * @brief Set BURTC compare channel
   *
   * @param[in] comp Compare channel index, must be 0 for Giant / Leopard Gecko
   *
   * @param[in] value New compare value
   ******************************************************************************/
  void BURTC_CompareSet(unsigned int comp, uint32_t value)
  {
    (void) comp;  /* Unused parameter when EFM_ASSERT is undefined. */
  
    EFM_ASSERT(comp == 0);
  
    /* Modification of COMP0 register requires sync with potential ongoing
     * register updates in LF domain. */
    regSync(BURTC_SYNCBUSY_COMP0);
  
    /* Configure compare channel 0 */
    BURTC->COMP0 = value;
  }
  
  
  /***************************************************************************//**
   * @brief Get BURTC compare value
   *
   * @param[in] comp Compare channel index value, must be 0 for Giant/Leopard.
   *
   * @return Currently configured value for this compare channel
   ******************************************************************************/
  uint32_t BURTC_CompareGet(unsigned int comp)
  {
    (void) comp;  /* Unused parameter when EFM_ASSERT is undefined. */
  
    EFM_ASSERT(comp == 0);
  
    return BURTC->COMP0;
  }
  
  
  /***************************************************************************//**
   * @brief Reset counter
   ******************************************************************************/
  void BURTC_CounterReset(void)
  {
    /* Set and clear reset bit */
    BUS_RegBitWrite(&BURTC->CTRL, _BURTC_CTRL_RSTEN_SHIFT, 1);
    BUS_RegBitWrite(&BURTC->CTRL, _BURTC_CTRL_RSTEN_SHIFT, 0);
  }
  
  
  /***************************************************************************//**
   * @brief
   *   Restore BURTC to reset state
   * @note
   *   Before accessing the BURTC, BURSTEN in RMU->CTRL must be cleared.
   *   LOCK will not be reset to default value, as this will disable access
   *   to core BURTC registers.
   ******************************************************************************/
  void BURTC_Reset(void)
  {
    bool buResetState;
  
    /* Read reset state, set reset and restore state */
    buResetState = BUS_RegBitRead(&RMU->CTRL, _RMU_CTRL_BURSTEN_SHIFT);
    BUS_RegBitWrite(&RMU->CTRL, _RMU_CTRL_BURSTEN_SHIFT, 1);
    BUS_RegBitWrite(&RMU->CTRL, _RMU_CTRL_BURSTEN_SHIFT, buResetState);
  }
  
  
  /***************************************************************************//**
   * @brief
   *   Get clock frequency of the BURTC.
   *
   * @return
   *   The current frequency in Hz.
   ******************************************************************************/
  uint32_t BURTC_ClockFreqGet(void)
  {
    uint32_t clkSel;
    uint32_t clkDiv;
    uint32_t frequency;
  
    clkSel = BURTC->CTRL & _BURTC_CTRL_CLKSEL_MASK;
    clkDiv = (BURTC->CTRL & _BURTC_CTRL_PRESC_MASK) >> _BURTC_CTRL_PRESC_SHIFT;
  
    switch (clkSel)
    {
      /** Ultra low frequency (1 kHz) clock */
      case BURTC_CTRL_CLKSEL_ULFRCO:
        if (_BURTC_CTRL_PRESC_DIV1 == clkDiv)
        {
          frequency = 2000;     /* 2KHz when clock divisor is 1. */
        }
        else
        {
          frequency = SystemULFRCOClockGet();  /* 1KHz when divisor is different
                                                  from 1. */
        }
        break;
  
      /** Low frequency RC oscillator */
      case BURTC_CTRL_CLKSEL_LFRCO:
        frequency = SystemLFRCOClockGet() / (1 << clkDiv); /* freq=32768/2^clkDiv */
        break;
  
      /** Low frequency crystal osciallator */
      case BURTC_CTRL_CLKSEL_LFXO:
        frequency = SystemLFXOClockGet() / (1 << clkDiv); /* freq=32768/2^clkDiv */
        break;
  
      default:
        /* No clock selected for BURTC. */
        frequency = 0;
    }
    return frequency;
  }
  
  
  /** @} (end addtogroup BURTC) */
  /** @} (end addtogroup emlib) */
  
  #endif /* BURTC_PRESENT */
  