source: PROJECT_CORE_MPI/CORE_MPI/TRUNK/FIfo_proc.vhd

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-- Company: 
-- Engineer: 
-- 
-- Create Date:    04:35:05 10/15/2012 
-- Design Name: 
-- Module Name:    FIfo_mem - Behavioral 
-- Project Name: 
-- Target Devices: 
-- Tool versions: 
-- Description: 
--
-- Dependencies: 
--
-- Revision: 
-- Revision 0.01 - File Created
-- Additional Comments: 
--
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library IEEE; 
use IEEE.std_logic_1164.all; 
use IEEE.std_logic_unsigned.all; 
entity FIFO_LOGIC is 
 generic (N: integer := 3); 
 port (CLK, PUSH, POP, INIT: in std_logic; 
  ADD: out std_logic_vector(N-1 downto 0); 
  FULL, EMPTY, WE, NOPUSH, NOPOP: buffer std_logic); 
end entity FIFO_LOGIC; 
architecture RTL of FIFO_LOGIC is 
signal WPTR, RPTR: std_logic_vector(N-1 downto 0); 
signal LASTOP: std_logic; 
begin 
SYNC: process (CLK) begin 
 if (CLK'event and CLK = '1') then 
  if (INIT = '1') then  -- initialization -- 
   WPTR <= (others => '0'); 
   RPTR <= (others => '0'); 
   LASTOP <= '0'; 
  elsif (POP = '1' and EMPTY = '0') then  -- pop -- 
   RPTR <= RPTR + 1; 
   LASTOP <= '0'; 
  elsif (PUSH = '1' and FULL = '0') then  -- push -- 
   WPTR <= WPTR + 1; 
   LASTOP <= '1'; 
  end if;  -- otherwise all Fs hold their value -- 
 end if; 
end process SYNC;
COMB: process (PUSH, POP, WPTR, RPTR, LASTOP, FULL, EMPTY) begin 
-- full and empty flags -- 
 if (RPTR = WPTR) then 
  if (LASTOP = '1') then 
      FULL  <=  '1'; 
   EMPTY <= '0'; 
    else 
      FULL  <=  '0'; 
   EMPTY <= '1'; 
  end if; 
 else 
  FULL <= '0'; 
  EMPTY <= '0'; 
 end if; 
-- address, write enable and nopush/nopop logic -- 
 if (POP = '0' and PUSH = '0') then -- no operation -- 
  ADD <= RPTR; 
  WE <= '0'; 
  NOPUSH <= '0'; 
  NOPOP <= '0'; 
 elsif (POP = '0' and PUSH = '1') then -- push only -- 
  ADD <= WPTR; 
  NOPOP <= '0'; 
  if (FULL = '0') then -- valid write condition -- 
   WE <= '1'; 
   NOPUSH <= '0'; 
  else     -- no write condition -- 
   WE <= '0'; 
   NOPUSH <= '1'; 
  end if; 
 elsif (POP = '1' and PUSH = '0') then -- pop only -- 
  ADD <= RPTR; 
  NOPUSH <= '0'; 
  WE <= '0'; 
  if (EMPTY = '0') then -- valid read condition -- 
   NOPOP <= '0'; 
    else 
   NOPOP <= '1';  -- no red condition -- 
  end if; 
 else   -- push and pop at same time - 
  if (EMPTY = '0') then -- valid pop -- 
  ADD <= RPTR; 
   WE <= '0'; 
   NOPUSH <= '1'; 
   NOPOP <= '0'; 
    else 
   ADD <= wptr; 
   WE <= '1'; 
   NOPUSH <= '0'; 
   NOPOP <= '1'; 
  end if; 
 end if; 
end process COMB; 
end architecture RTL;