Ethercat random jitter fix

endian wrote:

 
I saw at my own eyes synchronization of 120 seconds with beckhoff SoE AX5125 driver with older firmware ... its not odd behaviour 

beckhoff IPCs have sometime very similar behaviour with their own hardware from my close experiences...

The more i read here about ethercat = the less i like it.
Thank you for pointing out the quirks, not only the good stuff.
 

ethercat is the best from the best ... everything has some + / - ... finally synchronization issues and these childhood illnesses are not fault of the ethercat protocol itselft which is very robust... Its issue of HW at side of master, slave or connection itself ... 

If we use native bckhff driver at native stuff around these issues are suppressed limiting to zero ...

 

I’ve been following this thread with interest all along. What surprises me, though, is that I haven’t experienced the jitter issues described so far. I’d be interested to know what hardware you’re using. Perhaps there’s a correlations 

andrax wrote:

I’ve been following this thread with interest all along. What surprises me, though, is that I haven’t experienced the jitter issues described so far. I’d be interested to know what hardware you’re using. Perhaps there’s a correlations 

Its never been an issue for me  either. I did wonder the other day if newer hardware was  not a concern.

Theoretically the problem is there. 
Some drives may be better than others to conceal the problem.
When you use syncToRefClock and don't hear it you will not hear it.
I mean the drives will not suddenly start being noisy.
The chance of hearing it is roughly every servo loop time/jitter start of linuxcnc.
With 7 microseconds jitter, you can hear it every 142'nd start of linuxcnc.
And you hear it throughout the linuxcnc session.

I thought my drives were immune to this, but after carefully listening I found they also
experience this, but they don't sound awful, just a very mild "tic".
The drives don't have to make noises, but they should definitely react to it.
It's basically a disturbance in the position flow, requesting an artificially very high or low acceleration.

I've used LeadShine and XingJie same issues with both, there may well be mitigations on the servos side for some manufacturer, but that does not mean the standard of Ethercat says they should be doing such a thing. So it's luck?

The linuxcnc-ethercat current release does not respect the ethercat standard, it has time phasing issues, this is demonstrably true.
Anyone lucky enough to not experience any issue has:
Incredibly low latency
Servos that somehow adjust phasing themselves further than what the Ethercat standard dictates.
CPU with instruction execution timing consistency across processes, somehow doing the phasing properly even if the code did not directly intended it.
Some servo feature that filters the commanded position.
Not used pos-cmd mode.
Not actively been looking for it, restarting 100+ times and induced high latency, and looking at Ferror and servo-thread in the halscope.

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Even if some hardware is not bothered by wrong phasing, you should not blame this on the servo drives manufacturers. The software they are interfacing with demonstrably does NOT respect the communication standard.