Hello All,
We are currently developing an URCap that should communicate with a PLC via a TCP/IP connection.
The goal is to display PLC-messages and error messages directly in the robot’s Installation tab in a dedicated user interface.
To achieve this, we implemented a TCP server (port 31003) on the robot side, which opens automatically when the URCap starts.
This server is started via a small systemd service and a netcat listener script generated from the URCap’s Java contribution class.
At first, everything works correctly:
• The port is opened successfully (LISTEN status confirmed via netstat – tlnp),
• The PLC can connect and exchange messages with the URCap.
After a few minutes, however, the port closes automatically, even though the systemd service is initially active.
We are looking for answers for the following questions:
1. Is there a supported method to keep a custom TCP port permanently open for communication with a PLC?
2. Are there any URCap API functions or secure interfaces (other than RTDE or the dashboard/secondary ports) that allow a persistent inbound TCP connection?
3. If not, is there a way to whitelist a custom systemd service so that it remains active after a reboot?
Thanks a lot in advance!