The lnphost package comes with a simple application called lnpdump. It is a multi-protocol packet monitor that can be a useful utility to debug all kinds of communication issues. The program receives all packets the tower can get and displays them interpreted or as raw bytes. Output format and communication parameters can be set by a set of command line parameters.
Usage: lnpdump [options] Dump all packets received from the Lego Mindstorms tower Options: -a, --all show packets even if they are invalid -d, --device device set tower device name -f, --fast use 4800 instead of 2400 baud -h, --help show this summary -m, --mask n LNP addressing layer mask, default 0xf0 -p, --noparity legOS compatibility mode -r, --raw don't interpret packages (implies --all) If no tower device name is specified, it is taken from the environment variable RCXTTY or the default setting /dev/ttyS0. Copyright 2004 Stephan Höhrmann, published under the GPL.