use POSIX;
use Fcntl;

use sigtrap qw(die untrapped);


sub SIGIO_Handler {
  my $signame = shift;
  print "Somebody sent me a SIG$signame\n";
}

$SIG{IO} = \&SIGIO_Handler;


$| = 1;
open(LINK, "+</dev/ttyS0") || die "Can't connet to the device: $!";

my $termios = new POSIX::Termios;

$termios->getattr( fileno(LINK) );

my $c_cflag = $termios->getcflag;
my $c_lflag = $termios->getlflag;

$c_cflag |= (CLOCAL | CREAD | CS8);
$c_cflag &= ~(PARENB);
$c_cflag &= ~(CSTOPB);
$c_cflag |=  (CSIZE);

$c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
$c_oflag &= ~(OPOST);

$termios->setcc(VMIN,   0);
$termios->setcc(VTIME, 10);

$termios->setcflag($c_cflag);
$termios->setlflag($c_lflag);
$termios->setoflag($c_oflag);

$termios->setispeed(B2400);
$termios->setospeed(B2400);

$termios->setattr( fileno(LINK), TCSAFLUSH);

# -- Register "myself" ($$) to catch SIGIOs.
fcntl(LINK, &Fcntl::F_SETOWN, $$);
fcntl(LINK, F_SETFL, O_ASYNC);


print LINK "AT\r";

while (1) {
  # -- Just wait and ...
  # -- see if any SIGIO arrives
};