[Etherlab-users] load when reading SDOs

[Mittermeier Franz]

Hello all,

i try to read some SDOs from a slave, the PDOs are limited and that values need not to be updated with high frequency.

My first trial was using the function "ecrt_master_sdo_upload" in a non realtime task.
Problem here besides of the blocking behaviour is, that it needs the slave position and not its alias,
which i think is a problem in case of dynamically connected/disconnected slaves.

So i tried using the methods "ecrt_slave_config_create_sdo_request, ecrt_sdo_request_timeout ,ecrt_sdo_request_read, ecrt_sdo_request_state, ecrt_sdo_request_data"
in the realtime task.
That works, but with this i see a process "EtherCAT-OP" in the task list with a cpu load of more than 20%, while my test application consumes about 1%.
This is for reading only one SDO. Without reading the SDO "EtherCAT-OP" is also at about 1% load.

So my question, does reading one SDO really cause this high cpu load? Is there something wrong? Or am i on a totally wrong way to read some SDOs?

My test application is mainly derived from the "user" example, of course i can share the source if of interest.
It uses a cycle time of 5ms, so it should be not too fast.
It runs on a plc (Cortex A8) with Preempt_rt patch, etherCAT version is 1.6.1.
There are 4 slaves connected, 3 Beckhoff and one NORD inverter, from which I need to read the SDOs.

I really appreciate receiving some tips!

Best regards
Franz
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