To run the simulation in hardware-in-the-loop mode, we entered the following lines into omnetpp.ini:
[General] scheduler-class = "cSocketRTScheduler"
This selects the cSocketRTScheduler class as scheduler class. This class expects another configuration entry, socketrtscheduler-port=, which specifies the TCP port to listen on. The default port is 4242; you can change it to e.g. 6000 by adding the following line under [General]:
socketrtscheduler-port=6000