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--
--	fifo.vhd
--
--	simple fifo
--
--	uses FF and every rd or wr has to 'bubble' through the hole fifo.
--	
--	Author: Martin Schoeberl	martin.schoeberl@chello.at
--
--
--	resources on ACEX1K
--
--		(width+2)*depth-1 LCs
--
--
--	2002-01-06	first working version
--	2002-11-03	a signal for reaching threshold
--	2005-02-20	change entity order for modelsim vcom
--
 
library ieee;
use ieee.std_logic_1164.all;
 
entity fifo_elem is
 
generic (width : integer);
port (
	clk		: in std_logic;
	reset	: in std_logic;
 
	din		: in std_logic_vector(width-1 downto 0);
	dout	: out std_logic_vector(width-1 downto 0);
 
	rd		: in std_logic;
	wr		: in std_logic;
 
	rd_prev	: out std_logic;
	full	: out std_logic
);
end fifo_elem;
 
architecture rtl of fifo_elem is
 
	signal buf		: std_logic_vector(width-1 downto 0);
	signal f		: std_logic;
 
begin
 
	dout <= buf;
 
process(clk, reset, f)
 
begin
 
	full <= f;
 
	if (reset='1') then
 
		buf <= (others => '0');
		f <= '0';
		rd_prev <= '0';
 
	elsif rising_edge(clk) then
 
		rd_prev <= '0';
		if f='0' then
			if wr='1' then
				rd_prev <= '1';
				buf <= din;
				f <= '1';
			end if;
		else
			if rd='1' then
				f <= '0';
			end if;
		end if;
 
	end if;
 
end process;
 
end rtl;
 
library ieee;
use ieee.std_logic_1164.all;
 
entity fifo is
 
generic (width : integer := 8; depth : integer := 4; thres : integer := 2);
port (
	clk		: in std_logic;
	reset	: in std_logic;
 
	din		: in std_logic_vector(width-1 downto 0);
	dout	: out std_logic_vector(width-1 downto 0);
 
	rd		: in std_logic;
	wr		: in std_logic;
 
	empty	: out std_logic;
	full	: out std_logic;
	half	: out std_logic
);
end fifo ;
 
architecture rtl of fifo is
 
component fifo_elem is
 
generic (width : integer);
port (
	clk		: in std_logic;
	reset	: in std_logic;
 
	din		: in std_logic_vector(width-1 downto 0);
	dout	: out std_logic_vector(width-1 downto 0);
 
	rd		: in std_logic;
	wr		: in std_logic;
 
	rd_prev	: out std_logic;
	full	: out std_logic
);
end component;
 
	signal r, w, rp, f	: std_logic_vector(depth-1 downto 0);
	type d_array is array (0 to depth-1) of std_logic_vector(width-1 downto 0);
	signal di, do		: d_array;
 
 
 
begin
 
 
	g1: for i in 0 to depth-1 generate
 
		f1: fifo_elem generic map (width)
			port map (clk, reset, di(i), do(i), r(i), w(i), rp(i), f(i));
 
		x: if i<depth-1 generate
			r(i) <= rp(i+1);
			w(i+1) <= f(i);
			di(i+1) <= do(i);
		end generate;
 
	end generate;
 
	di(0) <= din;
	dout <= do(depth-1);
	w(0) <= wr;
	r(depth-1) <= rd;
 
	full <= f(0);
	half <= f(depth-thres);
	empty <= not f(depth-1);
 
end rtl;