#!/usr/bin/perl -w

use strict;
use Device::SerialPort qw( :PARAM :STAT 0.07 );
use Term::ANSIColor qw(:constants);

print YELLOW,"Location of device: ",RESET;
my $port = <>; # prompt for device, eg: /dev/tty0
chomp $port;

my $rootDir = "~";

my $config = "$rootDir/.testconf";

open(LOG,">>$rootDir/test.log");
print LOG "started\n";

# protocol-specific control chars
my %IM = (
  'SOM'  => chr(2),   #Start of message (STX)
  'EOM'  => chr(3),   #End of message (ETX)
  'AFF'  => chr(6),   #Affirmative Acknowledge (ACK)
  'NEG'  => chr(21),  #Negative Acknowledge (NAK)
  'POL'  => chr(5),   #Poll for data (ENQ)
  'SEL'  => chr(7),   #Alarm (BEL)
  'EOR'  => chr(13),  #End of record (CR)
  'DLE'  => chr(16),  #DLE
  'RES'  => chr(4),   #Reset (EOT)
  'ESOM' => chr(15),  #On Error, Start of Message (SI)
  'EEOM' => chr(14),  #On Error, End of Message (SO)
);

print "\nCreating config file...\n";

my $PortObj = new Device::SerialPort ($port) || die("Can't open $port:
+ $^E\n\n");

$PortObj->databits(7);
$PortObj->baudrate(19200);
$PortObj->parity("even");
$PortObj->stopbits(1);
$PortObj->handshake("xoff");
$PortObj->buffers(4096, 4096);

$PortObj->write_settings || undef $PortObj;

$PortObj->save("$config");

$PortObj->close || die("failed to close\n\n");

if(defined $PortObj)
{ print YELLOW, "Success!\n", RESET; }
else
{ die("PortObj is undefined!\n\n"); }

undef $PortObj;

print LOG "config file created and saved\n";

print "\nTie()ing to port...\n";
$PortObj = tie (*SERIAL, 'Device::SerialPort', "$config")
              || die("Can't open $port: $^E\n\n");

# use non-blocking read on serial port
$PortObj->read_char_time(5);
$PortObj->read_const_time(500);

print YELLOW, "Success!\n",RESET;
print LOG "tied to serial port\n";

my $EXIT = 0;
$SIG{'INT'} = sub { $EXIT = 1 };

my $data;

while($EXIT == 0)
{
  print "\nPolling for data...\n";
  $data = pollForData();
  print YELLOW, "Success!\n",RESET;

  print "\nData: ",GREEN,"$data",RESET;
}

print LOG "stopping\n";
close(LOG);

print "\n\n";

$PortObj->close || die("failed to close");
untie *SERIAL;
undef $PortObj;

exit;

sub pollForData
{
  my($length,$buffer,$lrc,$input);

  $buffer = join('',RED,"NO DATA",RESET);

  print SERIAL $IM{'POL'};

    $length = read(SERIAL,$buffer,4096);

  if($buffer eq '')
  { return join('',RED,"BLANK STRING",RESET); }

  if(!defined $buffer)
  { return join('',RED,"UNDEFINED STRING",RESET); }

  if($buffer ne $IM{'RES'})
  {  print SERIAL $IM{'AFF'}; }

  # otherwise, return data
  return $buffer;
}
[download]

when this is run, it saves and loads the config file without a problem, tie()s to a filehandle without a problem, and then prints "NO DATA" in the loop, meaning it doesnt match '' or undef...

i'm stumped, could anyone please help me?