-// Parse serial port option --serial=/dev/ttyS1,nmea,4800,out
+// Parse I/O channel option
+//
+// Format is "--protocol=medium,direction,hz,medium_options,..."
+//
+// protocol = { native, nmea, garmin, fgfs, rul, pve, etc. }
+// medium = { serial, socket, file, etc. }
+// direction = { in, out, bi }
+// hz = number of times to process channel per second (floating
+// point values are ok.