ModbusTCP Server sockets max number

[ticoti]

Hi to everyone again! I've been dealing with PLC IDE in order to set up a ModbusTCP server. Works fine after read some examples.

Once running, it accepts up to three working sockets (three paralell clients). Is it possible to increase this value?

I found this answer for Arduino boards:

Arduino Ethernet Shield 2 Socket Limit

I'm using an Arduino Ethernet Shield 2 and the datasheet says that it supports up to eight simultaneous socket connections. My questions is what happens when there are more than eight connections, are the connections queued, waiting for a free socket or are they rejected?

But no luck on Opta on PLC IDE 1.0.3

[steve9]

Hi, I'm not sure if this applies equally to the Opta as it does to the GIGA, but on the GIGA I needed to follow the instructions below to build a custom version of the libmbed.a library having added

      "lwip.socket-max": 12,
      "lwip.tcp-socket-max": 10,

to the mbed_app.json file.

variants/OPTA/conf/mbed_app.json

Why, with all the resources of these boards, Arduino took a conservative approach with some of the configuration is a mystery to me.

GitHub - arduino/ArduinoCore-mbed

[ledsyn]

Perhaps this can shed some insight:

tcp sockets memory usage Arduino

[ppp-one]

Hey Any luck increasing the max socket number?

[ticoti]

Hi @ppp-one , not tried yet. I reported the issue to Arduino support and got a kind email. Acoording to it, Arduino is actively working to address this behaviour, but there is not release date to solve this. I've checked that the server releases the orphaned sockets afters a few hours, but this expiry should be a few minutes.

My latest planed trick to solve this is a modbus-based countdown watchdog.