1 --------------------------------------------------------------------------
2 --
3 -- Copyright (C) 1993, Peter J. Ashenden
4 -- Mail: Dept. Computer Science
5 -- University of Adelaide, SA 5005, Australia
6 -- e-mail: petera@cs.adelaide.edu.au
7 --
8 -- This program is free software; you can redistribute it and/or modify
9 -- it under the terms of the GNU General Public License as published by
10 -- the Free Software Foundation; either version 1, or (at your option)
11 -- any later version.
12 --
13 -- This program is distributed in the hope that it will be useful,
14 -- but WITHOUT ANY WARRANTY; without even the implied warranty of
15 -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
16 -- GNU General Public License for more details.
17 --
18 -- You should have received a copy of the GNU General Public License
19 -- along with this program; if not, write to the Free Software
20 -- Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
21 --
22 --------------------------------------------------------------------------
23 --
24 -- $RCSfile: alu-behaviour.vhdl,v $ $Revision: 1.1 $ $Date: 2000/05/08 14:36:47 $
25 --
26 --------------------------------------------------------------------------
27 --
28 -- Behavioural architecture of ALU.
29 --
30
31
32 architecture behaviour of alu is
33
34 begin
35
36 alu_op: process (s1, s2, latch_en, func)
37
38 use work.bv_arithmetic.all;
39
40 variable stored_s1, stored_s2 : dlx_word;
41 variable temp_result : dlx_word;
42 variable temp_overflow : boolean;
43
44 begin
45 if latch_en = '1' then
46 stored_s1 := s1;
47 stored_s2 := s2;
48 end if;
49 case func is
50 when alu_pass_s1 =>
51 temp_result := stored_s1;
52 when alu_pass_s2 =>
53 temp_result := stored_s2;
54 when alu_and =>
55 temp_result := stored_s1 and stored_s2;
56 when alu_or =>
57 temp_result := stored_s1 or stored_s2;
58 when alu_xor =>
59 temp_result := stored_s1 xor stored_s2;
60 when alu_sll =>
61 temp_result := bv_sll(stored_s1, bv_to_natural(stored_s2(27 to 31)));
62 when alu_srl =>
63 temp_result := bv_srl(stored_s1, bv_to_natural(stored_s2(27 to 31)));
64 when alu_sra =>
65 temp_result := bv_sra(stored_s1, bv_to_natural(stored_s2(27 to 31)));
66 when alu_add =>
67 bv_add(stored_s1, stored_s2, temp_result, temp_overflow);
68 when alu_addu =>
69 bv_addu(stored_s1, stored_s2, temp_result, temp_overflow);
70 when alu_sub =>
71 bv_sub(stored_s1, stored_s2, temp_result, temp_overflow);
72 when alu_subu =>
73 bv_subu(stored_s1, stored_s2, temp_result, temp_overflow);
74 end case;
75 result <= temp_result after Tpd;
76 zero <= bit'val(boolean'pos(temp_result = dlx_word'(X"0000_0000"))) after Tpd;
77 negative <= temp_result(0) after Tpd;
78 overflow <= bit'val(boolean'pos(temp_overflow)) after Tpd;
79 end process alu_op;
80
81 end behaviour;
82
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