nanogui: Thread: An average accurate periodic timer

Hi,

Let us consider two situations where current periodic timer is not
accurate.

Situation 1

If we create a periodic timer with period not a multiple of 10ms, say
25ms,

    GrCreateTimer(wid, 25, GR_TRUE);

we expect there will be 40 timer events come from server in 1 second.
But in fact it is not true, because the system timer resolution is
10ms.  The above statement is equivalent to

    GrCreateTimer(wid, 30, GR_TRUE);

Situation 2

If the system is busy executing some other processes, so that the
NanoX server is suspended for 100ms, then a few timer events are lost.


What I want from periodic timer is, although each timer event may not
arrives accurately, the average time should be accurate.  That is to
say, there should be exactly 40 timer events come from server in 1
second if the timer period is 25ms.

To solve this problem, I modify slightly the way to calculate new
timeout value.  Instead of base on current time, I calculate it base
on old timeout value.  Please see the patch below.

I believe it is not of gerenal interest.  But it is useful to me.

Regards,
Sheng


--- microwin-aph/src/engine/devtimer.c  Mon Apr  8 10:30:18 2002
+++ microwin-aph-new/src/engine/devtimer.c      Wed Aug 28 09:34:31 2002
@@ -65,6 +65,7 @@
 static struct timeval current_time;

 static void calculate_timeval(struct timeval *tv, MWTIMEOUT to);
+static void calculate_timeval_strict(struct timeval *tv, MWTIMEOUT to);
 static signed long time_to_expiry(struct timeval *t);

 MWTIMER *GdAddTimer(MWTIMEOUT timeout, MWTIMERCB callback, void *arg,
@@ -159,7 +160,7 @@
                if(time_to_expiry(&t->timeout) <= 0) {
                        t->callback(t->arg);
                         if(!t->periodic) GdDestroyTimer(t);
-                        else calculate_timeval(&t->timeout, t->period);
+                        else calculate_timeval_strict(&t->timeout,
t->period);
                }
                t = n;
        }
@@ -175,6 +176,16 @@
 {
        tv->tv_sec = current_time.tv_sec + (to / 1000);
        tv->tv_usec = current_time.tv_usec + ((to % 1000) * 1000);
+       if(tv->tv_usec > 1000000) {
+               tv->tv_sec++;
+               tv->tv_usec -= 1000000;
+       }
+}
+
+static void calculate_timeval_strict(struct timeval *tv, MWTIMEOUT to)
+{
+       tv->tv_sec += (to / 1000);
+       tv->tv_usec += ((to % 1000) * 1000);
        if(tv->tv_usec > 1000000) {
                tv->tv_sec++;
                tv->tv_usec -= 1000000;


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: What I want from periodic timer is, although each timer event may not
: arrives accurately, the average time should be accurate.  That is to
: say, there should be exactly 40 timer events come from server in 1
: second if the timer period is 25ms.

To solve this problem, perhaps the third argument to GrCreateTimer
should be the type of timer, not just a boolean for periodic or not.

I haven't yet added Alex's GrCreateTimer patch, since it changes the
API and will break existing programs.  I will be adding it creating
a GrCreateTimerEx entry point, with GrCreateTimer #defined
to the new *Ex entry point.  

Comments?

Regards,

Greg




: 
: To solve this problem, I modify slightly the way to calculate new
: timeout value.  Instead of base on current time, I calculate it base
: on old timeout value.  Please see the patch below.
: 
: I believe it is not of gerenal interest.  But it is useful to me.
: 
: Regards,
: Sheng
: 
: 
: --- microwin-aph/src/engine/devtimer.c  Mon Apr  8 10:30:18 2002
: +++ microwin-aph-new/src/engine/devtimer.c      Wed Aug 28 09:34:31 2002
: @@ -65,6 +65,7 @@
:  static struct timeval current_time;
: 
:  static void calculate_timeval(struct timeval *tv, MWTIMEOUT to);
: +static void calculate_timeval_strict(struct timeval *tv, MWTIMEOUT to);
:  static signed long time_to_expiry(struct timeval *t);
: 
:  MWTIMER *GdAddTimer(MWTIMEOUT timeout, MWTIMERCB callback, void *arg,
: @@ -159,7 +160,7 @@
:                 if(time_to_expiry(&t->timeout) <= 0) {
:                         t->callback(t->arg);
:                          if(!t->periodic) GdDestroyTimer(t);
: -                        else calculate_timeval(&t->timeout, t->period);
: +                        else calculate_timeval_strict(&t->timeout,
: t->period);
:                 }
:                 t = n;
:         }
: @@ -175,6 +176,16 @@
:  {
:         tv->tv_sec = current_time.tv_sec + (to / 1000);
:         tv->tv_usec = current_time.tv_usec + ((to % 1000) * 1000);
: +       if(tv->tv_usec > 1000000) {
: +               tv->tv_sec++;
: +               tv->tv_usec -= 1000000;
: +       }
: +}
: +
: +static void calculate_timeval_strict(struct timeval *tv, MWTIMEOUT to)
: +{
: +       tv->tv_sec += (to / 1000);
: +       tv->tv_usec += ((to % 1000) * 1000);
:         if(tv->tv_usec > 1000000) {
:                 tv->tv_sec++;
:                 tv->tv_usec -= 1000000;
: 
: 
: __________________________________________________
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: Yahoo! Finance - Get real-time stock quotes
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