pascal / winpcap example ... i don't get any packets

pcapdemo.pas

{$mode delphi}
program pcapdemo;
uses pcap, sysutils, crt;

procedure throw(msg:string; detail:pchar);
  begin raise Exception.Create(msg + ': ' + detail)
  end;

function IPv4ToStr(addr:dword) : string;
  // this probably exists somewhere but i don't know where.
  type asbytes = array[0..3] of byte;
  var i, b : byte;
  begin
    for i := 0 to 3 do begin
      result += intToStr(asbytes(addr)[i]);
      if i < 3 then result += '.';
    end;
  end;

var
  err : pchar;
  cap  : ppcap;
  dev, devs : ppcap_if;
  addr, mask : dword;
  prog : Tbpf_program;
  head : Tpcap_pkthdr;
  pack : pchar;
  filter : pchar = ''; //tcp port 80';
  choice, count : word;

const
  kPcapOptimize = 1;
  kPcapNoOptimize = 0;
  kPcapOK = 0;
  kPCapError = -1;
  kPcapPromiscuous = 1;
  kSnaplen = 64; // chars to capture
  kTimeout = 1000; // milliseconds
begin
  err := stralloc(PCAP_ERRBUF_SIZE);
  try

    // name := pcap_lookupdev(err);
    // if name = nil then throw('error looking up device', err);

    if pcap_findalldevs(@devs, err) <> kPCapOK
    then throw('error listing all devices', err);

    {-- choose which device to monitor --}
    dev := devs; count := 0;
    repeat
      writeln(count:3, ' ', dev^.description);
      dev := dev^.next; inc(count);
    until dev = nil;

    if count = 0 then choice := 0
    else begin

      repeat write('which? (0-', count, ')'); readln(choice);
      until (choice >= 0) and (choice < count);

      dev := devs; count := 0;
      while count < choice do begin
        dev := dev^.next; inc(count);
      end
    end;

    {-- set up the connection --------}

    if pcap_lookupnet(dev^.name, @addr, @mask, err) <> kPCapOK
    then throw('error looking up net details', err);

    cap := pcap_open_live(dev^.name, ksnaplen, kPcapPromiscuous, kTimeout, err);
    if cap = nil then throw('error opening live', err);

    if pcap_compile(cap, @prog, filter, kPcapNoOptimize, mask) <> kPcapOK
    then throw('error compiling program', pcap_geterr(cap));

    if pcap_setfilter(cap, @prog) <> kPcapOK
    then throw('error setting filter', pcap_geterr(cap));

    writeln;
    writeln('device : ', dev^.name, ' (', dev^.description, ')');
    writeln('address: ', IPv4ToStr(addr));
    writeln('filter : ', filter);
    writeln;

    writeln('listening...');
    writeln('----------------------------------------------');
    repeat
      if pcap_next_ex(cap, @head, @pack) <> kPcapError
      then writeln(head.len, ' ', pack); // <-- always 0 and empty string
    until keypressed;

  except
    on e:exception do writeln(e.message)
  end;
  pcap_close(cap); pcap_freealldevs(devs);
  readln;
end.