- Intital revision

git-svn-id: http://moon:8086/svn/vhdl/trunk@86 cc03376c-175c-47c8-b038-4cd826a8556b

lib/misc/ram_sim.vhd

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+-------------------------------------------------------------------------
+-- Project: JCPU, a portable 8-bit RISC CPU written in VHDL
+-- This file: The ROM file for use in your VHDL design
+--
+-- Copyright (C) 2007 J. Ahrensfeld
+--
+-- 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 3 of the License, 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, see <http://www.gnu.org/licenses/>.
+--
+-- For questions and ideas, please contact the author at jens@jayfield.org
+--
+--------------------------------------------------------------------------
+
+LIBRARY ieee;
+use IEEE.STD_LOGIC_1164.ALL;
+USE ieee.numeric_std.ALL;
+
+
+ENTITY ram IS
+	Generic 
+	(
+		word_addr_width 	: integer := 6
+	);
+	Port 
+	(
+		clk			: in  STD_LOGIC;
+		ce			: in  STD_LOGIC;
+		we			: in  unsigned(3 downto 0);
+		addr		: in  unsigned(31 downto 0);
+		din			: in  unsigned(31 downto 0);
+		dout		: out unsigned(31 downto 0)
+	);
+END ram;
+
+ARCHITECTURE behavior OF ram IS 
+
+	constant depth : natural := 2**word_addr_width;
+	
+	type sram_t is array (0 to depth-1) of unsigned(31 downto 0);
+
+	function sram_clear return sram_t is
+
+	variable result : sram_t;
+	begin
+		for i in 0 to sram_t'length-1 loop
+			result(i) := (others => '0');
+		end loop;
+		return result;
+	end sram_clear;
+
+	signal sram : sram_t := sram_clear;
+	
+BEGIN
+
+
+SRAM_RW:
+	process(clk)
+	variable index : natural range 0 to depth-1;
+	begin
+		if rising_edge(clk) and ce = '1' then
+			index := to_integer(addr(word_addr_width+1 downto 2));
+			if we(0) = '1' then
+				sram(index)(7 downto 0)		<= din(7 downto 0);
+			end if;	
+			if we(1) = '1' then
+				sram(index)(15 downto 8)	<= din(15 downto 8);
+			end if;	
+			if we(2) = '1' then
+				sram(index)(23 downto 16)	<= din(23 downto 16);
+			end if;	
+			if we(3) = '1' then
+				sram(index)(31 downto 24)	<= din(31 downto 24);
+			end if;	
+			dout <= sram(index);
+		end if;	
+	end process;
+	
+end behavior;