Hello all,

 I tried to implement circular buffer in vhdl.. I am getting partial o/p waveform when i tried to simulate it.

Library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

entity fifoeda is

generic (

B : natural :=8; -- number of bit

W: natural :=4 -- number of address bit

);

port (

clk, reset :  in std_logic;

rd, wr : in std_logic;

w_data : in std_logic_vector ( B-1 downto 0);

empty, full : out std_logic;

r_data : out std_logic_vector (B-1 downto 0)

);

end fifoeda;

architecture arch of fifoeda is

type reg_file_type is array (2**W-1 downto 0) of std_logic_vector (B-1 downto 0);

--signal array_reg: reg_file_type;

signal w_ptr_reg, w_ptr_next, w_ptr_succ: std_logic_vector(W-1 downto 0);

signal r_ptr_reg, r_ptr_next, r_ptr_succ: std_logic_vector(W-1 downto 0);

signal full_reg, empty_reg, full_next, empty_next: std_logic;

signal wr_op: std_logic_vector ( 1 downto 0);

signal wr_en: std_logic;

begin

--==============================================

--========register files=====

process(clk, reset)

variable array_reg : reg_file_type;

begin

if (reset='1') then

  array_reg:= (others=>(others=>'0'));

elsif (clk'event and clk='1') then

     if wr_en ='1' then

array_reg( to_integer( unsigned (w_ptr_reg))):=w_data;

     end if;

end if;

--end process;

-- read port

r_data<= array_reg( to_integer(unsigned(r_ptr_reg)));

-- write enable only when FIFO is not full

end process;

wr_en<= wr and (not full_reg);

--===================================================

-- fifo control logic

--===================================================

-- register for read and write pointers

process( clk, reset)

begin

     if ( reset= '1') then

w_ptr_reg <= (others=>'0');

r_ptr_reg  <= (others=>'0');

full_reg  <= '0';

empty_reg <= '1';

     elsif (clk' event and clk='1') then

w_ptr_reg<= w_ptr_next;

r_ptr_reg <= r_ptr_next;

full_reg <= full_next;

   empty_reg<= empty_next;

     end if;

end process;

-- successive pointer values

w_ptr_succ<= std_logic_vector (unsigned(w_ptr_reg)+1);

r_ptr_succ<= std_logic_vector (unsigned (r_ptr_reg)+1);

-- next-state logic for read and write pointers

wr_op <= wr& rd;

process( w_ptr_reg, w_ptr_succ, r_ptr_reg, r_ptr_succ, wr_op, empty_reg, full_reg)

begin

w_ptr_next <= w_ptr_reg;

r_ptr_next<= r_ptr_reg;

full_next <= full_reg;

empty_next <= empty_reg;

Case wr_op is

when "00" => -- no op

when "01" => -- read

if ( empty_reg /='1') then -- not empty

r_ptr_next<= r_ptr_succ;

full_next <= '0';

if ( r_ptr_succ = w_ptr_reg) then

    empty_next<= '1';

end if;

end if;

when "10" => -- write 

    if (full_reg /= '1') then -- not full

w_ptr_next <= w_ptr_succ;

empty_next<= '0';

if (w_ptr_succ = r_ptr_reg) then

full_next <= '1';

end if;

    end if;

when others=> -- write /read;

w_ptr_next <= w_ptr_succ;

r_ptr_next <= r_ptr_succ;

end case;

end process;

---==================out put=====

full<= full_reg;

empty <= empty_reg;

end arch;

full, empty signals are not activated in waveform and i even tried removing wr_en(as ref. to some article that circular buffer is a FIFO w/o write enable).

Can anyone help me out from this...

Thanks,

Kavya.