[etherlab-users] (libethercat) Reading list of all objects available in slaves object dictionary

[Gavin Lambert]

On 28 October 2016 22:13, quoth Frank Jeschke:
> Hi list, I'm implementing a EtherCAT master software using the 
> libethercat library. Now I need to read the list of all the 
> Objects in the device(s) object dictionary. Something similar 
> what I get with
> 
> $ ethercat sdos
> Sadly I couldn't find anything in the header ecrt.h which looks 
> like a function giving me desired result.
> 
> So my question is, is there another posibility with the use of 
> libethercat or do I have to hack something with the ioctl call 
> to retrieve the list of objects? 

The ecrt.h API are just the functions that real-time applications are expected to use.  This does include read/writes to known SDOs, but not diagnostic information such as reading the list of SDOs; those are left to the "tool" APIs, which are exposed only as ioctls.  You can have a look at the "tool" source for usage examples.

Bear in mind that fetching the object dictionary can be quite slow (several seconds per device), and is usually unnecessary in applications; unless you're trying to implement a "configurator" rather than a standard application.  In fact, one of the significant performance improvements in the unofficial patchset was to avoid fetching the dictionary at all most of the time.

Also note that while it is safe to call these while a real-time loop is running (though not in the real-time thread itself, since they're blocking), they do acquire locks and might increase your real-time latency.