I found a couple of errors in the Rabbit Net user’s manual, so hopefully this will help anyone having trouble with the rn_find function.
The documentation implies that the rn_search.port member is a bitmask for the ports (port 0 would be 0x01, port 1 0x02, both ports 0x03). This is incorrect. The port parameter is the port number, so to find a board connected to port 0 set the port member to 0. For a board connected to port 1 set port to 1.
Second, the documentation states that the function returns 0 if no device is found. In fact, it returns -1 if no board is found, just like the rn_device function.
Hopefully this will save someone some time and frustration.