sub is_serial_data_ready {
    print "is_serial_data_ready: enter\n";

    # Non-blocking read: otherwise, we'll hang up here!
    my $c = $port->input;

    print "is_serial_data_ready: got <$c>\n";

    # Process the incoming characters
    for my $char (split '', $c) {
        print "is_serial_data_ready: char '$char'\n";
        if ($char eq "\n" or $char eq "\r") {
            print "is_serial_data_ready: end-of-line found\n";
            # End of line found, add current line to buffer
            # (unless it's empty)
            if ($serial_input ne '') {
                push @serial_data, $serial_input;
                # start a new blank line
                $serial_input = "";
            }
        }
        else {
            # Just a normal character, add to the input
            $serial_input .= $char;
        }
    }

    # Returns true if there are any completed lines to handle
    print "is_serial_data_ready: ", join(" // ", @serial_data), ".\n";

    return scalar @serial_data;
}