[etherlab-users] yet another datagrams UNMATCHED - DC 0.2ms / 5kHz // igb kernel 3.18

Sebastien Blanchet blanchet at iram.fr
Wed Feb 14 14:37:14 CET 2018

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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