text: /* ----------------------------------------------------------------------------
   *         SAM Software Package License
   * ----------------------------------------------------------------------------
   * Copyright (c) 2011, Atmel Corporation
   *
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  /** \addtogroup rtt_module Working with RTT
   *  \ingroup peripherals_module
   * The RTT driver provides the interface to configure and use the RTT
   * peripheral.
   *
   * The Real-time Timer is used to count elapsed seconds.\n
   * This timer is clocked by the 32kHz system clock divided by a programmable
   * 16-bit value. To be accurate, it is better to use an
   * external 32kHz crystal instead of the internal 32kHz RC.\n
   *
   * To count elapsed seconds, the user could follow these few steps:
   * <ul>
   * <li>Programming PTPRES in RTT_MR to feeding the timer with a 1Hz signal.</li>
   * <li>Writing the bit RTTRST in RTT_MR to restart the timer with new settings.
   * </li>
   * </ul>
   *
   * An alarm can be set to happen on second by setting alarm value in RTT_AR.
   * Alarm occurrence can be detected by polling or interrupt.
   *
   * For more accurate information, please look at the RTT section of the
   * Datasheet.
   *
   * Related files :\n
   * \ref rtt.c\n
   * \ref rtt.h.\n
   */
  /*@{*/
  /*@}*/
  
  /**
   * \file
   *
   * Implementation of Real Time Timer (RTT) controller.
   *
   */
  
  /*----------------------------------------------------------------------------
   *        Headers
   *----------------------------------------------------------------------------*/
  #include "chip.h"
  
  #include <assert.h>
  
  /*----------------------------------------------------------------------------
   *        Exported functions
   *----------------------------------------------------------------------------*/
  
  /**
   * \brief Changes the prescaler value of the given RTT and restarts it.
   *
   * \note This function disables RTT interrupt sources.
   *
   * \param rtt  Pointer to a Rtt instance.
   * \param prescaler  Prescaler value for the RTT.
   */
  void RTT_SetPrescaler(Rtt *rtt, uint16_t prescaler)
  {
  	rtt->RTT_MR = (prescaler |  RTT_MR_RTTRST);
  }
  
  /**
   * \brief Returns the current value of the RTT timer value.
   *
   * \param rtt  Pointer to a Rtt instance.
   */
  uint32_t RTT_GetTime(Rtt *rtt)
  {
  	return rtt->RTT_VR;
  }
  
  /**
   * \brief Enables the specified RTT interrupt sources.
   *
   * \param rtt  Pointer to a Rtt instance.
   * \param sources  Bitmask of interrupts to enable.
   */
  void RTT_EnableIT(Rtt *rtt, uint32_t sources)
  {
  	assert( (sources & 0x0004FFFF) == 0 ) ;
  	rtt->RTT_MR |= sources;
  }
  
  /**
   * \brief Returns the status register value of the given RTT.
   *
   * \param rtt  Pointer to an Rtt instance.
   */
  uint32_t RTT_GetStatus(Rtt *rtt)
  {
  	return rtt->RTT_SR;
  }
  
  /**
   * \brief Configures the RTT to generate an alarm at the given time.
   *
   * \param pRtt  Pointer to an Rtt instance.
   * \param time  Alarm time.
   */
  void RTT_SetAlarm(Rtt *pRtt, uint32_t time)
  {
  	assert(time > 0);
  
  	pRtt->RTT_AR = time - 1;
  }
  