[etherlab-users] RTAI + DC: Extremely poor and inconsistent performance.

[Mohsen Alizadeh Noghani]

Hello everyone.
I can't consistently run a very simple EtherLab RTAI code
<https://github.com/mohse-n/L7N_EtherLab/blob/master/rtai/rtai_sample.c>
with distributed clocks at more than about 100 Hz! If I increase the
frequency, I usually get the EtherCAT error:
*AL status message 0x0032: "PLL error
<https://infosys.beckhoff.com/english.php?content=../content/1033/ethercatsystem/1072494091.html&id=>".*
Basically, the higher the frequency, the higher the likelihood of receiving
this error. I don't think the cause of this problem is on the RTAI side as
the RTAI latency test while the module executes shows a maximum latency of
less than 20 microseconds.
The weird thing is, I can run the same straightforward cyclic task in userspace
<https://github.com/mohse-n/L7N_EtherLab/blob/master/user/main.c>(with
non-rt kernel no less) at 3 KHz, with no skipped frames. I expect the RTAI
performance to be way better-not much worse-than userspace code.
Best,
Mohsen
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