bool flash::rewrite_option_bytes(OB_TypeDef const * new_values)
{
    FLASH->OPTKEYR = 0x45670123;
    FLASH->OPTKEYR = 0xCDEF89AB;
    if(!(FLASH->CR & FLASH_CR_OPTWRE))
        return false;
    FLASH->CR |= FLASH_CR_OPTER;
    FLASH->CR |= FLASH_CR_STRT;
    if(!wait(PAGE_ERASE_TIMEOUT))
        return false;
    uint16_t const * pNew = (uint16_t const *)new_values;
    uint16_t * pOld = (uint16_t *)OB;
    for(uint_fast8_t i = 0; i < sizeof(*OB) / sizeof(uint16_t); ++i)
    {
        if((*pNew & 0xFF) != (*pOld & 0xFF))
        {
            FLASH->CR = FLASH_CR_OPTPG;
            *pOld = *pNew;
            wait();
            FLASH->CR = 0;
            if((*pNew & 0xFF) != (*pOld & 0xFF))
                return false;
        }
        pNew++;
        pOld++;
    }
    return true;
}

/**
  * @brief  Erases the FLASH option bytes.
  * @note   This functions erases all option bytes except the Read protection (RDP).
  * @note   This function can be used for all STM32F10x devices.
  * @param  None
  * @retval FLASH Status: The returned value can be: FLASH_ERROR_PG,
  *         FLASH_ERROR_WRP, FLASH_COMPLETE or FLASH_TIMEOUT.
  */
FLASH_Status FLASH_EraseOptionBytes(void)
{
  uint16_t rdptmp = RDP_Key;

  FLASH_Status status = FLASH_COMPLETE;

  /* Get the actual read protection Option Byte value */
  if(FLASH_GetReadOutProtectionStatus() != RESET)
  {
    rdptmp = 0x00;  
  }

  /* Wait for last operation to be completed */
  status = FLASH_WaitForLastOperation(EraseTimeout);
  if(status == FLASH_COMPLETE)
  {
    /* Authorize the small information block programming */
    FLASH->OPTKEYR = FLASH_KEY1;
    FLASH->OPTKEYR = FLASH_KEY2;
    
    /* if the previous operation is completed, proceed to erase the option bytes */
    FLASH->CR |= CR_OPTER_Set;
    FLASH->CR |= CR_STRT_Set;
    /* Wait for last operation to be completed */
    status = FLASH_WaitForLastOperation(EraseTimeout);
    
    if(status == FLASH_COMPLETE)
    {
      /* if the erase operation is completed, disable the OPTER Bit */
      FLASH->CR &= CR_OPTER_Reset;
      
      /* Enable the Option Bytes Programming operation */
      FLASH->CR |= CR_OPTPG_Set;
      /* Restore the last read protection Option Byte value */
      OB->RDP = (uint16_t)rdptmp;
      /* Wait for last operation to be completed */
      status = FLASH_WaitForLastOperation(ProgramTimeout);

      if(status != FLASH_TIMEOUT)
      {
        /* if the program operation is completed, disable the OPTPG Bit */
        FLASH->CR &= CR_OPTPG_Reset;
      }
    }
    else
    {
      if (status != FLASH_TIMEOUT)
      {
        /* Disable the OPTPG Bit */
        FLASH->CR &= CR_OPTPG_Reset;
      }
    }  
  }
  /* Return the erase status */
  return status;
}