ERROR: Connection timed out: select

[Joe M.]

Hello all,

Observing a very sporadic ERROR: Connection timed out: select error using tcp.

I'm polling the slave device a rate of 1 second, with a resp timeout of 250ms. For the majority of the time, everything works flawlessly until this very occasional error occurs:

Waiting for a confirmation...
<0C><AC><00><00><00><0B><05><03><08><00><00><00><00><47><F8><41><06>
[0C][AD][00][00][00][06][05][04][00][01][00][06]
Waiting for a confirmation...
<0C><AD><00><00><00><0F><05><04><0C><4C><00><3F><99><14><00><42><4C><5F><64><41><1F>
[0C][AE][00][00][00][06][05][03][00][07][00][04]
Waiting for a confirmation...
<0C><AE><00><00><00><0B><05><03><08><00><00><00><00><47><F8><41><06>
[0C][AF][00][00][00][06][05][04][00][01][00][06]
Waiting for a confirmation...
<0C><AF><00><00><00><0F><05><04><0C><36><00><3F><9A><14><00><42><4C><5F><64><41><1F>
[0C][B0][00][00][00][06][05][03][00][07][00][04]
Waiting for a confirmation...
<0C><B0><00><00><00><0B><05><03><08><00><00><00><00><47><F8><41><06>
[0C][B1][00][00][00][06][05][04][00][01][00][06]
Waiting for a confirmation...
ERROR Connection timed out: select
0 bytes flushed

The same application runs on a Ubuntu Desktop with no issues; the above is from a VAR-SOM-MX6 target board.I've tried increasing the timeout but the same results occur. Noticed in another mail thread that using the modbus_set_slave() API resolved a similar issue, but that's already being done in the application code.

Any ideas on what to try/query/etc.?

Thanks

[Chuck Watson]

If you are NOT using a dedicated Ethernet network, you are attempting very fast polling with a short timeout. Other traffic on the network will cause issues with short timeouts.

 

Also, what is between your master and slave on the network? Any routers? Cheap switches?

 

What is the maximum timeout you have tried and still see the issue?

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[Joe Markel]

Thanks for responding.

5 seconds is the longest response time I tried (on the SoM), with similar results. The same application running on Ubuntu and the SoM were both on the same subnet, whereas the application ran for four days without error. I'm thinking of attaching Wireshark next to see just how quickly the slave is sending back a response.
 

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[Joe Markel]

Ok, the "connmand" process was chewing up too much CPU every 20 minutes or so. I killed the process and everything is working as-expected. Time to start tweaking.

On Thu, Apr 26, 2018 at 10:22 AM, Chuck Watson <wat...@gmail.com> wrote:

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