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+--------------------------------------------------------------------------
+--
+--  Copyright (C) 1993, Peter J. Ashenden
+--  Mail:	Dept. Computer Science
+--		University of Adelaide, SA 5005, Australia
+--  e-mail:	petera@cs.adelaide.edu.au
+--
+--  This program is free software; you can redistribute it and/or modify
+--  it under the terms of the GNU General Public License as published by
+--  the Free Software Foundation; either version 1, or (at your option)
+--  any later version.
+--
+--  This program is distributed in the hope that it will be useful,
+--  but WITHOUT ANY WARRANTY; without even the implied warranty of
+--  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+--  GNU General Public License for more details.
+--
+--  You should have received a copy of the GNU General Public License
+--  along with this program; if not, write to the Free Software
+--  Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+--
+--------------------------------------------------------------------------
+--
+--  $RCSfile: alu-behaviour.vhdl,v $  $Revision: 2.1 $  $Date: 1993/11/02 18:52:07 $
+--
+--------------------------------------------------------------------------
+--
+--  Behavioural architecture of ALU.
+--
+
+
+architecture behaviour of alu is
+
+begin
+
+  alu_op: process (s1, s2, latch_en, func)
+
+    use work.bv_arithmetic.all;
+
+    variable stored_s1, stored_s2 : dlx_word;
+    variable temp_result : dlx_word;
+    variable temp_overflow : boolean;
+
+  begin
+    if latch_en = '1' then
+      stored_s1 := s1;
+      stored_s2 := s2;
+    end if;
+    case func is
+      when alu_pass_s1 =>
+        temp_result := stored_s1;
+      when alu_pass_s2 =>
+        temp_result := stored_s2;
+      when alu_and =>
+        temp_result := stored_s1 and stored_s2;
+      when alu_or =>
+        temp_result := stored_s1 or stored_s2;
+      when alu_xor =>
+        temp_result := stored_s1 xor stored_s2;
+      when alu_sll =>
+        temp_result := bv_sll(stored_s1, bv_to_natural(stored_s2(27 to 31)));
+      when alu_srl =>
+        temp_result := bv_srl(stored_s1, bv_to_natural(stored_s2(27 to 31)));
+      when alu_sra =>
+        temp_result := bv_sra(stored_s1, bv_to_natural(stored_s2(27 to 31)));
+      when alu_add =>
+        bv_add(stored_s1, stored_s2, temp_result, temp_overflow);
+      when alu_addu =>
+        bv_addu(stored_s1, stored_s2, temp_result, temp_overflow);
+      when alu_sub =>
+        bv_sub(stored_s1, stored_s2, temp_result, temp_overflow);
+      when alu_subu =>
+        bv_subu(stored_s1, stored_s2, temp_result, temp_overflow);
+    end case;
+    result <= temp_result after Tpd;
+    zero <= bit'val(boolean'pos(temp_result = dlx_word'(X"0000_0000"))) after Tpd;
+    negative <= temp_result(0) after Tpd;
+    overflow <= bit'val(boolean'pos(temp_overflow)) after Tpd;
+  end process alu_op;
+  
+end behaviour;