(* receive related procedures are kept in this file *)

  procedure get_char(var character : integer);
    (* get an incoming character from a packet *)

    var
      temp, rec_data, rec_stat : integer;

    begin
      temp := 0;
      character := 0;
      abort := false;
      retry := false;

      repeat

        rec_stat := Port[$d] and $01 ; {rec byte ready?}
        if rec_stat <> 0 then (* there is a character pending *)
            character := Port[$c]; {get it from port}
        temp := bdos (6, $ff); {get char status from console}
        if temp >0 then
           if temp > $1f then character := temp  {it's an ascii char}
           else
           case temp of
             4: abort := true; {^d aborts }
             $0d : retry := true; {cr forces end of packet}
             end; {case}

      until ((rec_stat <> 0) or abort or retry); (* condition for exit *)
      if parity_type_var <> no_parity  then
        character := character and $7f; (* strip the parity bit *)
    end;

  procedure receive_packet;
    (* get a complete packet.  *)

    var
      rec_char, temp : integer;
      check_char, temp_char : char;
      check_ok : boolean;
      checksum, count, index : integer;


      procedure get_p_length;

        (* After getting a ^A, start of packet, the next character should be
           the length of the packet.  This procedure was pulled out of the
           main receive procedure to make it easier to handle a new packet
           coming in before the old one finished (characters lost, etc.)
        *)

        begin
          if not (abort or retry) then (* skip if forced by operator *)
            begin
              get_char(rec_char); (* we get a character *)
              checksum := rec_char; (* first char to checksum *)
              count := rec_char - 32; (* whats our packet length *)
            end;
        end;

    begin (* rec_packet *)
      checksum := 0; (* start with no checksum *)
      rec_packet := ''; (* no data in packet *)
      check_ok := false; (* if we haven't got a packet, it can't be any good *)
      packet_ok := false; (* same here *)
      repeat  (* get ^A *)
        get_char(rec_char);
      until ((rec_char = 1) or abort or retry);
      get_p_length; (* we got a ^A so we need the length of the packet *)
      if not (abort or retry) then
        begin
          repeat
            get_char(rec_char); (* should be packet type and data *)
            if rec_char = 1 then (* got new start of packet *)
              begin              (* clear ourselves out again *)
                rec_packet := '';
                get_p_length; (* get new length *)
              end
            else  (* must be a character *)
              begin
                rec_packet := rec_packet + chr(rec_char); (* add to packet *)
                checksum := checksum + rec_char; (* add in the checksum *)
                count := count - 1; (* decrement the character counter *)
              end;
          until (abort) or retry or (count = 0);
          packets_sent := packets_sent + 1; (* sent is a misnomer here *)
          if debug then (* show what we got *)
            begin
              gotoxy(1,12);
              write('rpack: ');
              for count := 1 to length(rec_packet) do (* print the packet *)
                begin
                  temp_char := rec_packet[count]; (* dummy for printing *)
                  if (temp_char > chr(127)) then (* 8th bit set *)
                    begin
                      write(''''); (* print ' to show 8th bit set *)
                      temp_char := chr(ord(temp_char) and $7f); (* strip eighth bit *)
                    end;                              (* and fall through *)
                  if (temp_char < ' ') then (* print ctl char with ^ *)
                    write('^' + ctl(temp_char))
                  else
                    write(temp_char); (* must be printable *)
                end;
            end;
          if not abort then (* lets check what we can about packet *)
            begin
              checksum := checksum - rec_char; (* subtract chksum char *)
              check_char := char40((checksum + ((checksum and 192) div 64))
                and 63);
              if debug then (* show the checksum expected and received *)
                begin
                  gotoxy(1,15);
                  write('Received checksum: ',rec_packet[length(rec_packet)],
                         ' Calculated checksum: ', check_char);
                end;
              if check_char = rec_packet[length(rec_packet)] then
                check_ok := true; (* good checksum *)
              rec_packet_num := unchar(rec_packet[1]); (* what kind of packet *)
              case rec_packet[2] of
                'B' : packet_type := break_pack;
                'D' : packet_type := data_pack;
                'E' : packet_type := error_pack;
                'F' : packet_type := header_pack;
                'N' : packet_type := nak_pack;
                'S' : packet_type := send_pack;
                'T' : packet_type := reserved_pack;
                'Y' : packet_type := ack_pack;
                'Z' : packet_type := end_pack;
                else packet_type := unknown;
              end; (* case *)
              if length(rec_packet) > 3 then (* clean off the packet number,
                                                packet type, and checksum *)
                begin
                  delete(rec_packet,1,2);
                  delete(rec_packet,length(rec_packet),1);
                end;
              if (check_ok) and (packet_type <> unknown) then
                packet_ok := true;
              if debug then
                begin
                  gotoxy(1,18);
                  write('packet ok: ',packet_ok);
                end;
            end;
        end;
    end; (* rec_packet *)