Bernhard Pfund wrote: > All, > > I know this is an often discussed topic and I'm sorry to bother you > again with it. > > Has anyone achieved TDMA cycles below 200us so far? Is short, I need to
I don't think so. > serve 8 slaves within 165us (~6kHz) and I was wondering if it's possible > using RTnet. The amount of data is very small, let's say 16bits per slot > (what a waste using GBit Ethernet ;) but, it's got to be _fast_ You would be surprised about how much 0.1 vs. 1 GBit/s actually matters with minimal packet sizes - compared to the remaining latencies and jitters of your whole system... > > Those also reading the RTAI list might have seen my latency/jitter > benchmarking with a very powerful Core 2 Quadcore machine. This machine > shall serve as the RTnet master, equipped with an Intel Pro/1000 NIC for > RT communication. [ Reading the mail. ] You've done the standard timer jitter test, maybe also not yet with optimal load (see [1]). Things become far uglier when you start using periphery, eg. the PCI bus. > > Jan once mentioned freqs somewhere below 10kHz should be possible using > a decent machine. well... is it doable? Maybe, but likely not without careful tweaking of the involved subsystems. Specifically, your application should perform 1-to-n communication where the server collects all states via unicasts from the slave and distributes updates via a single broadcast. And don't do other traffic on the line (no non-RT tunneling, no RTmac heartbeats after startup). That should scale quite well. So a simple 2-nodes test may already give you an impression of what is possible with your hardware and what not. Jan [1]http://www.rts.uni-hannover.de/xenomai/lxr/source/TROUBLESHOOTING#040
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