lib/sysutil/tickdelay.c

   1 #include "sysutil.h"
   2 #include <timers.h>
   3
   4 /*===========================================================================*
   5  *                               tickdelay                                   *
   6  *===========================================================================*/
   7 PUBLIC int tickdelay(ticks)
   8 long ticks;                             /* number of ticks to wait */
   9 {
  10 /* This function uses the synchronous alarm to delay for a while. This works
  11  * even if a previous synchronous alarm was scheduled, because the remaining
  12  * tick of the previous alarm are returned so that it can be rescheduled.
  13  * Note however that a long tick_delay (longer than the remaining time of the
  14  * previous) alarm will also delay the previous alarm.
  15  */
  16     message m, m_alarm;
  17     int s;
  18
  19     if (ticks <= 0) return OK;          /* check for robustness */
  20
  21     m.ALRM_ENDPT = SELF;                /* SELF means this process nr */
  22     m.ALRM_EXP_TIME = ticks;            /* request message after ticks */
  23     m.ALRM_ABS_TIME = 0;                /* ticks are relative to now */
  24     s = _taskcall(SYSTASK, SYS_SETALARM, &m);
  25     if (s != OK) return(s);
  26
  27     receive(CLOCK,&m_alarm);            /* await synchronous alarm */
  28
  29     /* Check if we must reschedule the current alarm. */
  30     if (m.ALRM_TIME_LEFT > 0 && m.ALRM_TIME_LEFT != TMR_NEVER) {
  31         m.ALRM_EXP_TIME = m.ALRM_TIME_LEFT - ticks;
  32         if (m.ALRM_EXP_TIME <= 0)
  33                 m.ALRM_EXP_TIME = 1;
  34         s = _taskcall(SYSTASK, SYS_SETALARM, &m);
  35     }
  36
  37     return(s);
  38 }
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