EtherCAT + Nerves

Questions & Help Questions
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Hi all, has anyone worked with EtherCAT and Nerves before?

I’m quite new with Ethercat, so I’m looking for a good starting point like a reliable and recommended library (and easy to use haa) that handles Ethercat that can be added to a nerves custom system.

Thanks in advance :slight_smile: .

2

I’ve worked with EtherCAT. Nerves uses Buildroot which includes an EtherCAT package igh-ethercat. It goes through the standard network stack. It also has a few hardware drivers such as e100 for better performance. To include it you need to make a custom Nerves system and add the package.

Ultimately, we found it didn’t have the performance we needed for our specific hardware. So we made a custom, private Nerves system that uses Acontis’s EtherCAT offering.

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Thanks for the answer, you give me a good path to follow !!! :).

If you do not mind to tell us, did you used the nerves official supported hardware or another one?
I’m asking it because I’m planning to use a Rpi3 and I want to know if it’s worth to looking at igh-ethercat or directly to the Arcontis, or which were your performance limitations that igh-ethercat doesn’t accomplished?
Also I want to ask:
In your opinion, which package is more friendly to use (or to make an elixir wrapper)?

Thanks in advance…

4

We had problems with igh-ethercat with raspberry pi. It simply couldn’t compile the igh-ethercat package. We never figured out why. It worked with BeagleBone Black and that’s what we’re still using.

We needed sub-millisecond response times on EtherCAT. igh-ethercat doesn’t provide hardware drivers for BBB (or RPi). So it was taking several milliseconds for a round trip.

If you don’t need that level of performance, then go with igh-ethercat. It’s also open source. Actontis provides proprietary, enterprise-level solutions so you’ll be paying quite a bit for it.

5

Hi all, here is an update of this thread; first, I tried to build igh-ethernet package in buildroot for a rpi3, however, since rpi3 doesn’t have any igh-ethernet supported hardware. The igh-ethernet needs to be compiled with --enable-generic option, therefore, I needed to add a custom igh-ethernet package to buildroot, also I enabled udev, taskset packages. Despite this, I had these types of warnings during compilation:

depmod: WARNING: /home/alde/Documents/Elixir/Nerves/repos/valiot_system_rpi3/.nerves/artifacts/valiot_system_rpi3-portable-1.7.2-valiot.7/target/lib/modules/4.19.25/extra/devices/ec_generic.ko needs unknown symbol kernel_bind

depmod: WARNING: /home/alde/Documents/Elixir/Nerves/repos/valiot_system_rpi3/.nerves/artifacts/valiot_system_rpi3-portable-1.7.2-valiot.7/target/lib/modules/4.19.25/extra/master/ec_master.ko needs unknown symbol sched_setscheduler
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The following error was shown during runtime:

iex(3)> cmd "modprobe ec_master"
modprobe: can't load module ec_master (extra/master/ec_master.ko): unknown symbol in module, or unknown parameter
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At this point I thought it could be a kernel version issue, since when compiling a similar repository (for bbb), the compilation works without warnings, therefore, I lost interest in using igh-ethernet haha.

The second option was the arcontis software atemsys, which it appears to be easier to compile, so I added a custom package to buildroot, however, during compilation I had the same type of warning (only 1 warning) as before:

depmod: WARNING: /home/alde/Documents/Elixir/Nerves/repos/valiot_system_rpi3/.nerves/artifacts/valiot_system_rpi3-portable-1.7.2-valiot.7/target/lib/modules/4.19.25/extra/atemsys.ko needs unknown symbol of_find_compatible_node

Therefore, it also fails at runtime.

My third option was the SOEM project, I had no issue with this library (compiles with no warnings), however, this package is refered by the community more as a library than a master software, therefore, I think that its better to make an Elixir wrapper than add the package in buildroot.

Giving another chance to the previous options (atmsys, igh-ethernet) and looking the bbb project, it seems that by disabling CONFIG_TRIM_UNUSED_KSYMS=y in linux-x.x.defconfig both packages works in runtime !!!

The option CONFIG_TRIM_UNUSED_KSYMS=y seem to be to trim exported kernel symbols that are not used, which for me seems that it makes the opposite, I also do not know what kind of problems I am creating when disabling this option :(, Does anyone knows?

Currently, the problem in which I am working with igh-ethernet is to open a device /dev/EtherCAT0 that does not exist, but I think it’s a matter of executing some package commands and defining some rules in /etc/udev/rule.d (this directory does not exist either).

Does anyone know how to define these rules in Nerves?, or does it have to be done in Buildroot?

Regards.

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If anyone is still stumbling upon this problem, I’ve written two libraries which are both running on <10ms cycle time on a Rpi4: