Hallo BigNose, I've just read the documentation of igh ethercat master, especially the chapter *4.2 Native EtherCAT Device Drivers*. It says, there is no need to have an interrupt, because the "communication is highly deterministic: A frame is sent and will be received again after a constant time" in the same network. Bad that I didn't read it before. So now I think, what we need to do, is to find out that constant time for our specific network by trial and error.
Best regards, Jun ---------- Forwarded message ---------- > From: +BigNose <bign...@bluewin.ch> > To: etherlab-users <etherlab-users@etherlab.org> > Cc: > Date: Wed, 14 Dec 2011 10:05:13 +0100 > Subject: Re: [etherlab-users] Knowing when the packet has finished cycle > Hallo Shahbaz, > > I encountered the exact same problem. So I'm happy, this topic get's > discussed. > > The problem is, that in a realtime control application, it is common, > that you wanna have the sensor values as fresh as possible. And as > Ethercat is very fast, this yields a good starting point. > > But just like you, I also encountered the problem, of how can you get > ASAP the data from the master. > > IMHO the main problem here is, that the interrupt capability of the > driver has been dropped. So that now it has to be polled. > > BTW: Why exactly has the interrupt capability been dropped? What is > the advantage of this? > "The interrupt-less operation is desirable, because hardware interrupts are not con- ducive in improving the driver’s realtime behaviour: Their indeterministic incidences contribute to increasing the jitter. Besides, if a realtime extension (like RTAI) is used, some additional effort would have to be made to prioritize interrupts." - chapter 4.2 To always poll, if the master has received, is IMHO a bit ressource > hungry, and as you said, I wouldn't know how to implement this > anyway, as you push the Master into an error, if you do it. > A maybe workable solution would be, as you said, if one can surely > determine, after how much time, one can surely 100% read the master. > > So I'm really very interested in this topic. > > Thank you > >
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