direct_implementation.vhdl

VHDL 实现 有限冲击响应滤波器的设计（直接式）

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;
USE ieee.numeric_std.ALL;

ENTITY direct_implementation IS
   GENERIC (WIDTH:INTEGER:=8;
            N:INTEGER:=4);
   PORT (reset,start:STD_LOGIC;
         x:IN STD_LOGIC_VECTOR(WIDTH-1 DOWNTO 0);
         y:OUT STD_LOGIC_VECTOR(2*WIDTH-1 DOWNTO 0));
END direct_implementation;

ARCHITECTURE arch_direct_implementation OF direct_implementation IS
TYPE const_array_type IS ARRAY(0 TO N-1) OF
              STD_LOGIC_VECTOR(WIDTH-1 DOWNTO 0);
TYPE sample_array_type IS ARRAY(1 TO N-1) OF
              STD_LOGIC_VECTOR(WIDTH-1 DOWNTO 0);

--CONSTANT const_array:mem_array:=("11011000",
--                                 "00011101",
--                                 "00011101",
--                                 "11011000");
CONSTANT const_array:const_array_type:=("00000001",
                                        "00000001",
                                        "00000001",
                                        "00000001");
SIGNAL sample_array:sample_array_type;

BEGIN
   FIR_process:
   PROCESS(reset,start)
   VARIABLE y_var:SIGNED(2*WIDTH-1 DOWNTO 0);
   BEGIN
      IF (reset='1') THEN
         y_var:=(OTHERS=>'0');
         sample_array(1)<="00001111";
         sample_array(2)<="00111100";
         sample_array(3)<="00011100";
--         sample_array(1)<="00000001";
--         sample_array(2)<="00000001";
--         sample_array(3)<="00000001";
      ELSIF (start='1') THEN
         y_var:=(OTHERS=>'0');
         y_var:=SIGNED(x)*SIGNED(const_array(0));
         FOR i IN 1 TO sample_array'HIGH LOOP
              y_var:=y_var+SIGNED(sample_array(i))*
                                 SIGNED(const_array(i));
         END LOOP;
         FOR i IN sample_array'HIGH DOWNTO 2 LOOP
            sample_array(i)<=sample_array(i-1);
         END LOOP;
         sample_array(1)<=x;
      END IF;
      y<=STD_LOGIC_VECTOR(y_var);
   END PROCESS FIR_process;
END arch_direct_implementation;