procedure Sound(Freq: Word);
var
  B: Byte;
begin
  if Freq > 18 then
  begin
    Freq := Word(1193181 div LongInt(Freq));
    B := Byte(GetPort($61));

    if (B and 3) = 0 then
    begin
      SetPort($61, Word(B or 3));
      SetPort($43, $B6);
    end;

    SetPort($42, Freq);
    SetPort($42, Freq shr 8);
  end;
end;

procedure NoSound;
var
  Value: Word;
begin
  Value := GetPort($61) and $FC;
  SetPort($61, Value);
end;

procedure SetPort(address, Value: Word);
var
  bValue: byte;
begin
  bValue := trunc(Value and 255);
  asm
    mov dx, address
    mov al, bValue
    out dx, al
  end;
end;

function GetPort(address: word): word;
var
  bValue: byte;
begin
  asm
    mov dx, address
    in al, dx
    mov bValue, al
  end;
  GetPort := bValue;
end;