[etherlab-users] R: Random Datagram Unmatched

[Dr.-Ing. Wilhelm Hagemeister]

Hallo Roberto,

Am 21.05.19 um 14:48 schrieb Viola Roberto:
> 
> This crc thing plus the packet’s counter thing by ifconfig push me to 
> think that sometimes the ec module ignores a packet even if ethernet 
> card receives it. Is is possible?

Yes that is possible. If you query the NIC to early after you send the 
frame, it might not be back yet. What is the order of your realtime 
execution? Is it receiving EtherCAT (the previous frame), processing, 
sending EtherCAT, waiting for next rt-schedule?

Due to jitter, or a to long execution time of your task, sending and 
receiving the EtherCAT frame might come to close. This might also 
explain why it is not a function of your cycle time. You have to monitor 
your execution time and cycle jitter to get to the problem.

> 
> What happen when EC gives me this warning? I mean, i will lost the 
> informations inside the unmatched packet for sure, but if this issue 
> happens when i write a SDO instead of a PDO the EC will retry 
> automatically to send another SDO packet?

If you accept frame drops, depends on your application. We usually 
accept a frame drop once in a while and don't trigger an emergency stop 
or likewise. SDO transfers are handled with state machines. If a request 
get's lost, it will be resent or will flag an error (which must be 
handled by your application).

Regards Wilhelm.