> Sercos 3 was one example of the use of ethernet for real time control. > > Another example is ethernet i/p. Again it uses standard ethernet technology > and allows the use of switches between the host and slave. It all comes > down to timing. AB claims they do +/- 100 uS without modified hardware. > With IEEE 1588 compliant hardware they can get it down much lower. It all > comes down to the application and what is required. > > Refer to ODVA's CIP Motion and CIP Sync for more information. > > I use AB PLC's and Bosch Rexroth drives using ethernet I/P communication > on a daily basis without 1588 hardware and have found it to offer exceptional > performance. > > My comments were relating to someone indicating that ethernet could not > be used in a real-time application.
RT-Net is a good candidate for an open source implementation. (http://www.rtnet.org/) RT-Net provides drivers for a collection of network cards that work under a real time kernel (RTAI). In its raw form, it can just be used to schedule delivery of Ethernet packets. You implement the protocol. To support real time communications, there are 3 specifications defined - rtmac, which defines the frame format, rtcfg, which is used by the master to find, and configure the slaves, and tdma (time division multiple access) which slices the bandwidth of the line into packets, then these packets sliced into slots. It also does clock synchronisation. The rtnet protocols can coexist with other Ethernet protocols on the line at the same time, but that seems a bit risky in a real time environment. There are some issues with it - the network card drivers seem to require a dedicated IRQ, so it can be hard to set up. The rtnet rtai software wants to control the rtai internal clock, so it needs to be made to play nicely with emc. It is open source, so theoretically a slave could be built on any microcontroller powerful enough to run an embedded linux, but it would still a realtime kernel and network drivers - I was looking and writing a dedicated slave firmware for the microcontroller. ------------------------------------------------------------------------------ Free Software Download: Index, Search & Analyze Logs and other IT data in Real-Time with Splunk. Collect, index and harness all the fast moving IT data generated by your applications, servers and devices whether physical, virtual or in the cloud. Deliver compliance at lower cost and gain new business insights. http://p.sf.net/sfu/splunk-dev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
