Hi Jürgen,

I can share with you some results with the 8139too and r8169 ethercat native drivers when used with RTAI and Preempt-RT kernel.


- with RTAI and 8139too you can achieve 10 KHz for the ethercat control loop without losing datagram. (tested on Debian 6.0 i386 with RTAI-3.8.1). The computer was a DELL Precision 390 with a Core Duo 2 processor, the slave were 4 Beckhoff Ethercat terminals (EL1004, EL2004, EL3102, EL4102).

- with Preempt-RT and r8169 you can achieve 1 KHz for the ethercat control loop without losing datagram. (tested on Debian 7.0 i386 with Debian RT kernel). At 2 KHz, it does not work very well (sometime you miss datagrams), so the limit is somewhere in the 1...2 KHz range. The computer is a Beckhoff C6920-0040 with the PCIe extension slots, and a Celeron B810 processor. The slaves are 4 Kollmorgen AKD servo drives + 13 other Ethercat terminals from Beckhoff.

Finally Preempt-RT is slower than RTAI, but it is really easier than RTAI.

best regards,
--
Sebastien BLANCHET




On 02/13/2018 02:12 PM, Christoph Schroeder wrote:
Hi Jürgen,

On 02/13/2018 10:01 AM, Jürgen Walter • DATATRONiQ wrote:
I see- will get another Intel card (although compatible ones (kernel driver e1000, e1000e) seem to be hard to come by these days) and try with anther kernel driver.
I also did some tests with the EtherCAT master, Xenomai and different network devices compatible with the ec_e1000e driver. Test system was a Core-i5 (4th generation) with a Debian Wheezy  (Kernel 3.2) with two slaves attached (Microship LAN9252 in simple Digital I/O mode). I observed the following:

  * even with the PREEMPT patch and the native driver ec_e1000e I could barely
    achieve 2000Hz cycle rate without frame losses
  * with Xenomai I could go over 10000Hz without a problem, but there are some
    other issues with Xenomai:
      o the EtherCAT master is not ready to use the newer Xenomai 3.x branch and
        the Xenomai 2.x branch is not supported anymore
      o I got some issues with long term stability on my test system (Kernel
        panic) and decided not to use it on a productive system
      o I would suggest you go for RTAI since you will also get far more help
        from the EtherCAT community, I could barely find other people here who
also use Xenomai with the EtherCAT master * while using Xenomai I observed, that there is also a huge difference between
    different network chips:
      o I initially used a card with an Intel 82572EI (introduced Q4'05) and
        also tried a Dual port card with an Intel 82571EB (introduced Q3'05)
        which had basically the same results on my test system
o the best results I got were achieved with an Intel 82574L (introduced Q2'0) I didn't try RTAI till now, but I think you will get the same or even better results than I got with Xenomai.

The cards with Intel 82574L we got were sold as "Intel Gigabit CT Desktop Adapter". The chip will be produced until 2020, so getting a card with it should be no problem. Maybe this will help you.


Best regards,
Christoph

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