Initial import

git-svn-id: http://moon:8086/svn/vhdl/trunk@5 cc03376c-175c-47c8-b038-4cd826a8556b

lib/FIFO/src/gray_counter.vhd

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+-------------------------------------------------------------------------
+-- Project: JCPU, a portable 8-bit RISC CPU written in VHDL
+-- This file: The call/return/data stack
+
+-- Copyright (C) 2007 J. Ahrensfeld
+
+-- This library is free software; you can redistribute it and/or
+-- modify it under the terms of the GNU Lesser General Public
+-- License as published by the Free Software Foundation; either
+-- version 2.1 of the License, or (at your option) any later version.
+
+-- This library 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
+-- Lesser General Public License for more details.
+
+-- You should have received a copy of the GNU Lesser General Public
+-- License along with this library; if not, write to the Free Software
+-- Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+
+-- For questions and ideas, please contact the author at jens@jayfield.org
+
+-----------------------------------------------------------------------
+-- $Header: /tmp/cvsroot/VHDL/lib/FIFO/src/gray_counter.vhd,v 1.1 2008-08-23 08:20:28 Jens Exp $
+-----------------------------------------------------------------------
+
+library IEEE;
+use IEEE.STD_LOGIC_1164.ALL;
+use IEEE.numeric_std.ALL;
+
+LIBRARY WORK;
+USE WORK.FIFO_CTRL_PKG.ALL;
+
+entity gray_counter is
+	Generic (
+		width : natural := 3;
+		init_value : natural := 0
+	);
+	Port
+	(
+		rst			: in  STD_LOGIC;
+		clk			: in  STD_LOGIC;
+		ce			: in  STD_LOGIC;
+		bcnt		: out unsigned (width-1 downto 0);
+		bnxt		: out unsigned (width-1 downto 0);
+		gcnt		: out unsigned (width-1 downto 0);
+		gnxt		: out unsigned (width-1 downto 0)
+	);
+end gray_counter;
+
+architecture Behavioral of gray_counter is
+
+	signal cntb : unsigned (width-1 downto 0);
+	signal nxtb : unsigned (width-1 downto 0);
+	signal cntg : unsigned (width-1 downto 0);
+	signal nxtg : unsigned (width-1 downto 0);
+
+begin
+
+	bnxt	<= nxtb;
+	gnxt	<= nxtg;
+
+	process(rst, clk, ce, cntb, nxtb)
+	begin
+		if rst = '1' then
+			cntb	<= to_unsigned(init_value, width);
+			nxtb	<= to_unsigned(init_value, width);
+			cntg	<= to_unsigned(init_value, width);
+			nxtg	<= to_unsigned(init_value, width);
+			bcnt	<= to_unsigned(init_value, width);
+			gcnt	<= to_unsigned(init_value, width);
+		else
+			if rising_edge(clk) then
+				bcnt	<= nxtb;
+				gcnt	<= nxtg;
+				cntb	<= nxtb;
+				cntg	<= nxtg;
+			end if;	
+			nxtg <= bin2gray(nxtb);
+			nxtb <= cntb;
+			if ce = '1' then
+				nxtb <= cntb + 1;
+			end if;	
+		end if;	
+	end process;
+
+end Behavioral;
+