I had a look at the source of the comp that latency-test uses
and I feel it is buggy
It measures the difference in time delay one tick to the next
not actual jitter from the system time
__s64 now = rtapi_get_time();
18 __s64 del = (now - last); //only check period of last tick
19 out = del;
20
21
22 if(last != 0) { //not first time through
23 err = err + del - period;
24 if(first) {
25 first = 0;
26 min_ = max_ = del;
27 jitter = 0;
28 } else {
29 if(del < min_) min_ = del;
30 if(del > max_) max_ = del;
31 jitter = max(max_ - period, period - min_); //
not checking this ticks time diff from where it should be
32 }
33 count++;
34 avg_err = err / (double)count;
35 }
I suggest keeping track of the correct ticktime with a
correct_time=period_counter*tick_period
and then something like
del=now-correct_time
actually do this and keep the current code so one can see short and
long term jitter
Dave Caroline
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