[etherlab-users] Domains and datagram timeouts.

Aaron Edsinger edsinger at csail.mit.edu
Wed Oct 7 17:10:23 CEST 2009

Hello. We've just bumped the total number of ET1200 slaves on our bus 
from 24 to 35. We're polling at 1Khz. We're now seeing messages like:

WARNING: 246 datagrams TIMED OUT!
WARNING: 24 datagrams UNMATCHED!
EtherCAT: Domain 0: 2 working counter changes - now 66/102

Reducing the poll rate to 100Hz doesn't fix the problem so I don't think 
  it is rate related. Subsets of slaves work fine, so we also don't 
think it is necessarily a hardware issue.

However, we're using a single domain of size 4080 bytes. This means the 
data image must be broken into 3 Ethernet frames. With 24 slaves we only 
required 2 frames. We're considering splitting the data image into 2+ 
domains, but I don't see that this should help. We'd like to keep comm. 
with all slaves at 1Khz if possible.

Does anyone see any gains to be made by splitting the image into 
multiple domains? Can someone offer an explanation as to why we're 
seeing the datagram timeout error?

Thanks in advance!

Aaron Edsinger, Ph.D.
San Francisco, CA

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