text: /*
      ChibiOS - Copyright (C) 2006..2016 Giovanni Di Sirio.
  
      This file is part of ChibiOS.
  
      ChibiOS is free software; you can redistribute it and/or modify
      it under the terms of the GNU General Public License as published by
      the Free Software Foundation; either version 3 of the License, or
      (at your option) any later version.
  
      ChibiOS is distributed in the hope that it will be useful,
      but WITHOUT ANY WARRANTY; without even the implied warranty of
      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      GNU General Public License for more details.
  
      You should have received a copy of the GNU General Public License
      along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
  
  /**
   * @file    chvt.c
   * @brief   Time and Virtual Timers module code.
   *
   * @addtogroup time
   * @details Time and Virtual Timers related APIs and services.
   * @{
   */
  
  #include "ch.h"
  
  /*===========================================================================*/
  /* Module local definitions.                                                 */
  /*===========================================================================*/
  
  /*===========================================================================*/
  /* Module exported variables.                                                */
  /*===========================================================================*/
  
  /*===========================================================================*/
  /* Module local types.                                                       */
  /*===========================================================================*/
  
  /*===========================================================================*/
  /* Module local variables.                                                   */
  /*===========================================================================*/
  
  /*===========================================================================*/
  /* Module local functions.                                                   */
  /*===========================================================================*/
  
  /*===========================================================================*/
  /* Module exported functions.                                                */
  /*===========================================================================*/
  
  /**
   * @brief   Virtual Timers initialization.
   * @note    Internal use only.
   *
   * @notapi
   */
  void _vt_init(void) {
  
    ch.vtlist.next = (virtual_timer_t *)&ch.vtlist;
    ch.vtlist.prev = (virtual_timer_t *)&ch.vtlist;
    ch.vtlist.delta = (systime_t)-1;
  #if CH_CFG_ST_TIMEDELTA == 0
    ch.vtlist.systime = (systime_t)0;
  #else /* CH_CFG_ST_TIMEDELTA > 0 */
    ch.vtlist.lasttime = (systime_t)0;
  #endif /* CH_CFG_ST_TIMEDELTA > 0 */
  }
  
  /**
   * @brief   Enables a virtual timer.
   * @details The timer is enabled and programmed to trigger after the delay
   *          specified as parameter.
   * @pre     The timer must not be already armed before calling this function.
   * @note    The callback function is invoked from interrupt context.
   *
   * @param[out] vtp      the @p virtual_timer_t structure pointer
   * @param[in] delay     the number of ticks before the operation timeouts, the
   *                      special values are handled as follow:
   *                      - @a TIME_INFINITE is allowed but interpreted as a
   *                        normal time specification.
   *                      - @a TIME_IMMEDIATE this value is not allowed.
   *                      .
   * @param[in] vtfunc    the timer callback function. After invoking the
   *                      callback the timer is disabled and the structure can
   *                      be disposed or reused.
   * @param[in] par       a parameter that will be passed to the callback
   *                      function
   *
   * @iclass
   */
  void chVTDoSetI(virtual_timer_t *vtp, systime_t delay,
                  vtfunc_t vtfunc, void *par) {
    virtual_timer_t *p;
    systime_t delta;
  
    chDbgCheckClassI();
    chDbgCheck((vtp != NULL) && (vtfunc != NULL) && (delay != TIME_IMMEDIATE));
  
    vtp->par = par;
    vtp->func = vtfunc;
  
  #if CH_CFG_ST_TIMEDELTA > 0
    {
      systime_t now = chVTGetSystemTimeX();
  
      /* If the requested delay is lower than the minimum safe delta then it
         is raised to the minimum safe value.*/
      if (delay < (systime_t)CH_CFG_ST_TIMEDELTA) {
        delay = (systime_t)CH_CFG_ST_TIMEDELTA;
      }
  
      /* Special case where the timers list is empty.*/
      if (&ch.vtlist == (virtual_timers_list_t *)ch.vtlist.next) {
  
        /* The delta list is empty, the current time becomes the new
           delta list base time, the timer is inserted.*/
        ch.vtlist.lasttime = now;
        ch.vtlist.next = vtp;
        ch.vtlist.prev = vtp;
        vtp->next = (virtual_timer_t *)&ch.vtlist;
        vtp->prev = (virtual_timer_t *)&ch.vtlist;
        vtp->delta = delay;
  
        /* Being the first element in the list the alarm timer is started.*/
        port_timer_start_alarm(ch.vtlist.lasttime + delay);
  
        return;
      }
  
      /* Pointer to the first element in the delta list, which is non-empty.*/
      p = ch.vtlist.next;
  
      /* Delay as delta from 'lasttime'. Note, it can overflow and the value
         becomes lower than 'now'.*/
      delta = now - ch.vtlist.lasttime + delay;
  
      if (delta < now - ch.vtlist.lasttime) {
        /* Scenario where a very large delay excedeed the numeric range, it
           requires a special handling. We need to skip the first element and
           adjust the delta to wrap back in the previous numeric range.*/
        delta -= p->delta;
        p = p->next;
      }
      else if (delta < p->delta) {
       /* A small delay that will become the first element in the delta list
          and next deadline.*/
        port_timer_set_alarm(ch.vtlist.lasttime + delta);
      }
    }
  #else /* CH_CFG_ST_TIMEDELTA == 0 */
    /* Delta is initially equal to the specified delay.*/
    delta = delay;
  
    /* Pointer to the first element in the delta list.*/
    p = ch.vtlist.next;
  #endif /* CH_CFG_ST_TIMEDELTA == 0 */
  
    /* The delta list is scanned in order to find the correct position for
       this timer. */
    while (p->delta < delta) {
      /* Debug assert if the timer is already in the list.*/
      chDbgAssert(p != vtp, "timer already armed");
  
      delta -= p->delta;
      p = p->next;
    }
  
    /* The timer is inserted in the delta list.*/
    vtp->next = p;
    vtp->prev = vtp->next->prev;
    vtp->prev->next = vtp;
    p->prev = vtp;
    vtp->delta = delta;
  
    /* Calculate new delta for the following entry.*/
    p->delta -= delta;
  
    /* Special case when the timer is in last position in the list, the
       value in the header must be restored.*/
    ch.vtlist.delta = (systime_t)-1;
  }
  
  /**
   * @brief   Disables a Virtual Timer.
   * @pre     The timer must be in armed state before calling this function.
   *
   * @param[in] vtp       the @p virtual_timer_t structure pointer
   *
   * @iclass
   */
  void chVTDoResetI(virtual_timer_t *vtp) {
  
    chDbgCheckClassI();
    chDbgCheck(vtp != NULL);
    chDbgAssert(vtp->func != NULL, "timer not set or already triggered");
  
  #if CH_CFG_ST_TIMEDELTA == 0
  
    /* The delta of the timer is added to the next timer.*/
    vtp->next->delta += vtp->delta;
  
   /* Removing the element from the delta list.*/
    vtp->prev->next = vtp->next;
    vtp->next->prev = vtp->prev;
    vtp->func = NULL;
  
    /* The above code changes the value in the header when the removed element
       is the last of the list, restoring it.*/
    ch.vtlist.delta = (systime_t)-1;
  #else /* CH_CFG_ST_TIMEDELTA > 0 */
    systime_t nowdelta, delta;
  
    /* If the timer is not the first of the list then it is simply unlinked
       else the operation is more complex.*/
    if (ch.vtlist.next != vtp) {
      /* Removing the element from the delta list.*/
      vtp->prev->next = vtp->next;
      vtp->next->prev = vtp->prev;
      vtp->func = NULL;
  
      /* Adding delta to the next element, if it is not the last one.*/
      if (&ch.vtlist != (virtual_timers_list_t *)vtp->next)
        vtp->next->delta += vtp->delta;
  
      return;
    }
  
    /* Removing the first timer from the list.*/
    ch.vtlist.next = vtp->next;
    ch.vtlist.next->prev = (virtual_timer_t *)&ch.vtlist;
    vtp->func = NULL;
  
    /* If the list become empty then the alarm timer is stopped and done.*/
    if (&ch.vtlist == (virtual_timers_list_t *)ch.vtlist.next) {
      port_timer_stop_alarm();
  
      return;
    }
  
    /* The delta of the removed timer is added to the new first timer.*/
    ch.vtlist.next->delta += vtp->delta;
  
    /* If the new first timer has a delta of zero then the alarm is not
       modified, the already programmed alarm will serve it.*/
  /*  if (ch.vtlist.next->delta == 0) {
      return;
    }*/
  
    /* Distance in ticks between the last alarm event and current time.*/
    nowdelta = chVTGetSystemTimeX() - ch.vtlist.lasttime;
  
    /* If the current time surpassed the time of the next element in list
       then the event interrupt is already pending, just return.*/
    if (nowdelta >= ch.vtlist.next->delta) {
      return;
    }
  
    /* Distance from the next scheduled event and now.*/
    delta = ch.vtlist.next->delta - nowdelta;
  
    /* Making sure to not schedule an event closer than CH_CFG_ST_TIMEDELTA
       ticks from now.*/
    if (delta < (systime_t)CH_CFG_ST_TIMEDELTA) {
      delta = (systime_t)CH_CFG_ST_TIMEDELTA;
    }
  
    port_timer_set_alarm(ch.vtlist.lasttime + nowdelta + delta);
  #endif /* CH_CFG_ST_TIMEDELTA > 0 */
  }
  
  /** @} */
  