method private port_to_positions port =
let port = port + 1 in (* kludge to implement 0-based numbering... *)
match lines, show_100_mbs, port <= (ports / 2) with
1, false, _ -> [ port - 1, 0 ]
| 2, false, true -> [ port - 1, 0 ]
| 2, false, false -> [ port - (ports / 2) - 1, 2 ]
| 1, true, _ -> [ port - 1, 0; port - 1, 1 ]
| 2, true, true -> [ port - 1, 0; port - 1, 1 ]
| 2, true, false -> [ port - (ports / 2) - 1, 3; port - (ports / 2) - 1, 4 ]
| _ -> assert false