1
2-- Copyright (C) 1996 Morgan Kaufmann Publishers, Inc
3
4-- This file is part of VESTs (Vhdl tESTs).
5
6-- VESTs is free software; you can redistribute it and/or modify it
7-- under the terms of the GNU General Public License as published by the
8-- Free Software Foundation; either version 2 of the License, or (at
9-- your option) any later version.
10
11-- VESTs is distributed in the hope that it will be useful, but WITHOUT
12-- ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13-- FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14-- for more details.
15
16-- You should have received a copy of the GNU General Public License
17-- along with VESTs; if not, write to the Free Software Foundation,
18-- Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
19
20-- ---------------------------------------------------------------------
21--
22-- $Id: ch_08_fg_08_06.vhd,v 1.1.1.1 2001-08-22 18:20:48 paw Exp $
23-- $Revision: 1.1.1.1 $
24--
25-- ---------------------------------------------------------------------
26
27package cpu_types is
28
29  constant word_size : positive := 16;
30  constant address_size : positive := 24;
31
32  subtype word is bit_vector(word_size - 1 downto 0);
33  subtype address is bit_vector(address_size - 1 downto 0);
34
35  type status_value is ( halted, idle, fetch, mem_read, mem_write,
36                         io_read, io_write, int_ack );
37
38  subtype opcode is bit_vector(5 downto 0);
39
40  function extract_opcode ( instr_word : word ) return opcode;
41
42  constant op_nop : opcode := "000000";
43  constant op_breq : opcode := "000001";
44  constant op_brne : opcode := "000010";
45  constant op_add : opcode := "000011";
46  -- . . .
47
48end package cpu_types;
49
50
51
52-- not in book
53
54package body cpu_types is
55
56  function extract_opcode ( instr_word : word ) return opcode is
57  begin
58    return work.cpu_types.op_nop;
59  end function extract_opcode;
60
61end package body cpu_types;
62
63-- end not in book
64