use Device::SerialPort;
my $port=Device::SerialPort->new("/dev/ttyS0");
$port->baudrate(9600);
$port->parity("none");
$port->handshake("none");
$port->databits(8);
$port->stopbits(1);
$port->read_char_time(0);
$port->read_const_time(1);

my $readChars=0; # init
my $readBytes=""; # init

while(1) # yes, I know this thread is blocking
{
   ($readChars, $readBytes)=$port->read(1);

   if ($readChars ne 0)
   {
      print("$readBytes"); # $Rval = $readBytes when attempting to share from thread to main window
      $readBytes=""; # re-init
   }
}