Hi, I CC'ed the RTnet list as well because this can quickly become RTnet-specific.
[EMAIL PROTECTED] wrote: > Hello everybody! > > I'm working on Realtime-Ethernet in conjunction with Distributed Clocks. > I wonder if anybody ever tried the following combination: > > RTAI + RTNet + Distributed Clocks > Yes (of course ;) ), our more complex robots uses RTnet for synchronising (and distributing) sensor data in real-time. An older example is [1]. Our accuracy requirements /wrt data time stamps are fairly low (~1 ms), though. > > For synchronisation of the clocks I would use the Precision Time Protocol > (PTP) (see IEEE1588). An Daemon for PTP can be found here > http://ptpd.sf.net > > With this solution you could synchronise actions up to a sub-microseconds > level independent from the amount of stations taking part in the > RT-Communication. Be warned about the patent situation with IEEE1588. I once considered to aim for integrating related support in RTnet but dropped the idea because it looked to me (IANAL) like that protocol (or better: an implementation in some device) is contaminated. > > Are there similar projects - or has anybody ever worked on > timestamping/distributed clocks? Depending on your requirements (accuracy, number of nodes, network structure, etc.) RTnet's TDMA service may already provide what you need. If not: any (non-1588) enhancement of RTnet's still fairly dumb synchronisation protocol would be warmly welcome! Maybe something like NTP over RTnet? I'm not so deep into what advantages PTP provides over NTP, except that the former typically runs on dedicated hardware or makes use of hardware-based packet time stamping to reduce software related jitters. There is currently quite a lot of work on efficient NTP for the Linux kernel going on ("scaled math"), maybe this is also worth a look. RTnet would prefer to see an efficient solution :) since it may run on fairly low-end boxes. Jan [1]http://www.rts.uni-hannover.de/images/b/b6/RTS_STILL_EURON_Technology_Transfer_Award.pdf
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