# start quick and EXTREMELY dirty xmodem transfert
sub xmodemrecv
{
  print $sock "\x15"; #NAK 
  A000: while(1) {
    SOH: while(1) {
      if (sysread($sock,$buf,1) <= 0) { die "*** died$! ***\n"; } #SOH
      last SOH if ( $buf eq "\x01" ) || ( $buf eq "\x04" )
    }
    # leave if last byte received is an EOT
    last A000 if ($buf eq "\x04");
    # last byte received was SOH
    if (sysread($sock,$buf,1) <= 0) { die "*** died$! ***\n"; }
    $seq = unpack("c",$buf);
    if (sysread($sock,$buf,1) <= 0) { die "*** died$! ***\n"; }
    $cseq = unpack("c",$buf); 
    $mseq = - ($seq & 255) -1; # just for fun we calculate the cmpl seq as well
    if (sysread($sock,$buf,128) <= 0) { die "*** died$! ***\n"; }
    $sum = 0;
    for ($i = 0; $i < 128; $i++) {
      $sum += unpack("c",substr($buf,$i,1));
    } 
      $sum = pack("c",($sum & 255)); 
    print "$buf";
    if (sysread($sock,$buf,1) <= 0) { die "*** died$! ***\n"; }
    $crc = $buf; 
    if ($crc eq $sum) {
      # packet ok 
      print $sock "\x06"; #ACK
    } else { 
      # packet nok - crc differs
      print $sock "\x15"; #NAK
    }
  }
  print $sock "\x06"; #ACK
}