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 ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ RTnet-users mailing list RTnet-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/rtnet-users
