#!/usr/bin/perl -w

use POSIX;

$port = '2';

$fd = POSIX::open('/dev/ttyS'. $port, O_RDWR | O_NOCTTY) or die "$! in open";
$termios = POSIX::Termios->new;
$termios->getattr($fd) or die "$! in getattr";
print $termios->getispeed, " ", $termios->getospeed, " ", POSIX::B9600, " ", POSIX::B38400, "\n";

POSIX::tcflush($fd, &POSIX::TCIOFLUSH);
$buff = '!!SP2!SE';
POSIX::write($fd, $buff, 8);

my $rin = '';
my $rout;
vec($rin, fileno(STDIN), 1) = 1;

my $sonar_in = '';
my $sonar_out;
vec($sonar_in, $fd, 1) = 1;

#
# wait 1/20 second, or until keypress; if keypress, STOP!
#
until (select($rout=$rin, undef, undef, 0.5) == 1) {

    POSIX::tcflush($fd, &POSIX::TCIOFLUSH);
    $buff = '!!SR';
    POSIX::write($fd, $buff, 4);
    $sonar_dist = 0;
    do {
	if (select ($sonar_out=$sonar_in, undef, undef, 0.5) == 1)
	{
	    while (!defined ($ret = POSIX::read($fd,$sonar_buff, 1))) {
		print "<\n";
	    };
	    if ($sonar_buff !~ /\n/) {
		$sonar_dist = $sonar_dist * 10 + $sonar_buff;
	    };
	}
	else {
	    $sonar_buff = "\n";
	    $sonar_dist = "TIMEOUT";
	}
    } until ($sonar_buff =~ /\n/);

    print "$sonar_dist\n";
};

END {
    $buff = '!!SD';
  POSIX::write($fd, $buff, 4);
  POSIX::close($fd);
}