nuttx/sched/clock_abstime2ticks.c

/********************************************************************************
 * clock_abstime2ticks.c
 *
 *   Copyright (C) 2007, 2008 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <gnutt@nuttx.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 * 3. Neither the name NuttX nor the names of its contributors may be
 *    used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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 ********************************************************************************/

/********************************************************************************
 * Included Files
 ********************************************************************************/

#include <nuttx/config.h>

#include <time.h>
#include <errno.h>
#include <debug.h>
#include "clock_internal.h"

/********************************************************************************
 * Definitions
 ********************************************************************************/

/********************************************************************************
 * Private Type Declarations
 ********************************************************************************/

/********************************************************************************
 * Global Variables
 ********************************************************************************/

/********************************************************************************
 * Private Variables
 ********************************************************************************/

/********************************************************************************
 * Private Functions
 ********************************************************************************/

/********************************************************************************
 * Public Functions
 ********************************************************************************/

/********************************************************************************
 * Name: clock_abstime2ticks
 *
 * Description:
 *   Convert an absolute timespec delay to system timer ticks.
 *
 * Parameters:
 *   clockid - The timing source to use in the conversion
 *   reltime - Convert this absolue time to system clock ticks.
 *   ticks - Return the converted number of ticks here.
 *
 * Return Value:
 *   OK on success; A non-zero error number on failure;
 *
 * Assumptions:
 *   Interrupts should be disabled so that the time is not changing during the
 *   calculation
 *
 ********************************************************************************/

int clock_abstime2ticks(clockid_t clockid, FAR const struct timespec *abstime,
                        FAR int *ticks)
{
  struct timespec currtime;
  struct timespec reltime;
  int             ret;

  /* Convert the timespec to clock ticks.  NOTE: Here we use internal knowledge
   * that CLOCK_REALTIME is defined to be zero!
   */

  ret = clock_gettime(clockid, &currtime);
  if (ret)
    {
      return EINVAL;
    }

  /* The relative time to wait is the absolute time minus the current time. */

  reltime.tv_nsec = (abstime->tv_nsec - currtime.tv_nsec);
  reltime.tv_sec  = (abstime->tv_sec  - currtime.tv_sec);

  /* Check if we were supposed to borrow from the seconds to borrow from the
   * seconds
   */

  if (reltime.tv_nsec < 0)
    {
      reltime.tv_nsec += NSEC_PER_SEC;
      reltime.tv_sec  -= 1;
    }

  /* Convert this relative time into microseconds. */

  return clock_time2ticks(&reltime, ticks);
}