Karl Reichert wrote: > Am Samstag, 28. Juli 2007 15:02 schrieb Jan Kiszka: > > Karl Reichert schrieb: > > > Jan Kizka wrote: > > >> Karl Reichert schrieb: > > >>> Sorry, some mistakes, please see correct settings ... > > >>> > > >>>> Hi everybody, > > >>>> > > >>>> I have a question concerning TDMA: > > >>>> > > >>>> When I set up RTnet with TDMA and a cycle length of 5000 ms, I get > an > > >>>> average master jitter (difference between scheduled and real > > >> > > >> transmission time > > >> > > >>>> of synchronisation frames) of less then 100 us, max 160 us. > > >>> > > >>> My setup was cycle length = 5000 us = 5 ms > > >>> > > >>>> When I do the same with cycle length 1000000 ms (1 second), I get > an > > >>>> average jitter of 8500 us (more then 8 ms). > > >>> > > >>> My setup was 1000000 us = 1000 ms = 1 s > > >>> > > >>>> With cycle length 2 seconds, I get an average jitter of 4500 us. > > >>> > > >>> My setup was 10000000 us = 10000 ms = 10 s > > >> > > >> What jitter do you get with the "latency" test running at the same > > >> periods? > > > > > > I assume we're talking about /usr/xenomai/bin/latency: > > > With 1 ms cycle length and latency tool running, jitter is much lower, > > > between 5-25 us. > > > > > > The other two cycle lengths & latency-tool I didn't gave a try, > because > > > this seems already strang to me. I'm very busy ATM but if testing with > > > those other cycles would help you with the problem, I could give you > the > > > values at end of august (when I'm finished with diploma). > > > > > >> What are the distributions of the jitters? All only around 4.5 > > >> or 8.5 ms, or are they spread over a far wider range than with 5 ms > > >> cycles? > > > > > > I general they spread little bit, but not very much, so I don't get > > > values higher then 5 ms / 9 ms. So this seems to be normal. > > > > > >> I can't look into this soon, but it has high priority for time I will > > >> have test equipment in reach again! > > > > > > Thanks Jan! Keep informed the list then, please ;) > > > Would really like to know why this happens, although it's not so > critical > > > to my project. > > > > So far I didn't find any systematic error with large cycle times. > > Capturing the outgoing master traffic, I got typical deltas of a few ten > > microseconds (unloaded system) according to Wireshark. That quick test > > took place over Xenomai trunk, but I would rather expect RTnet to be the > > problem here - if at all. > > > > One further important question to you: How did you measure / read out > > the master timing? Are you sure you didn't confuse micro- and > > nanoseconds here as well? Note that e.g. Wireshark reports all TDMA > > frame timing fields in _nanoseconds_ (all TDMA fields are in nanoseconds > > - to answer your older question). > > > > Jan > I read it via wireshark (with respect to nanoseconds) and also on my own > slave > implementation on TriCore 1130 via debugger. The values are really like > that. > I will send you a wireshark capture file on monday, so you can see on your > own > eyes! > > Karl > Please see attached wireshark capture file!
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