$ cat funky_i_o.pl
use strict;
use warnings;
use Term::ReadKey;
use Time::HiRes qw( alarm );

# Buffer used to build our command line
my $command_line = "";

# Buffer for our (fake) serial data
my @serial_data = ();

# Put console into raw mode
ReadMode 4;

setup_serial_interface();

my $are_we_done_yet = 0;
while (!$are_we_done_yet) {

    my $con_key = ReadKey(-1);
    if (defined $con_key) {
        if ($con_key eq "\r" or $con_key eq "\n") {
            # user finished entering the command
            handle_command($command_line);
            $command_line = "";
        }
        else {
            # Not end of line, so add to command line.
            # NOTE: you'll want to handle backspace and/or
            # other line editing commands.  But that's too
            # much work for a quick demo...
            $command_line .= $con_key;
        }
    }
    elsif (is_serial_data_ready()) {
        # Serial device gave us something to do
        handle_serial_data();
    }
    else {
        # Don't eat *ALL* the cpu, since nothing came in from
        # the console or serial line, pause a brief time to let
        # something arrive

        # Here, you'd normally use a sleep or usleep.  But alarm
        # and sleep aren't necessarily on friendly terms with each
        # other, and we're using alarm to fake a serial device. So
        # we're not actually going to delay here, but you would want
        # to in a real application.
    }
}

# Restore normal console mode
ReadMode(0);

sub handle_command {
    my $cmd = shift;
    if ($cmd =~ /^q/i) {
        print "Quitting!\n";
        $are_we_done_yet = 1;
    }
    elsif ($cmd =~ /^d.*(\d+)/i) {
        print "Starting a task that takes $1 seconds!\n";
        my $t = time;
        while ($t + $1 > time) {
            ; # fake process ... just wait until time expires
        }
        print "...and now we're done!\n";
    }
    else {
        print "Unknown command: $cmd\n";
    }
}

###
# Our fake serial interface
###

sub setup_serial_interface {
    my $seconds_per_transmission = 0.567;

    $SIG{ALRM} = sub {
        push @serial_data, rand;
        alarm $seconds_per_transmission;
    };

    # First packet of data should occur in a couple seconds
    alarm 2.5;
}

sub is_serial_data_ready {
    return scalar @serial_data;
}

sub handle_serial_data {
    print "We haz teh dataz! (", join(", ", @serial_data), ")\n";
    @serial_data = ();
}