fir filter.vhd

FIR Filter的例子

library maths;
library matrix;
library vfp;
library dsp;
architecture behavioural of FIR_32tap_8_8 is
  use maths.maths_functions.all;
  use matrix.matrix_class.all;
  use vfp.generic_functions.all;
  use vfp.generic_conversions.all;
  use vfp.mixed_operators.all;
  use vfp.twos_complement_types.all;
  constant number_of_taps: integer := 32;
  signal data_table: single_vector(number_of_taps-1 downto 0);
  signal coefficient_table: single_vector(number_of_taps-1 downto 0);
begin
  -- y <= sum_over (0, k-1, a((k-1)-i), b(i))
  -- coefficient_table <= b;
  fir_algorithm: process (clock)
    variable data_out : single;
    variable fir_result : single;
    variable data_table_var: single_vector(number_of_taps-1 downto 0);
    -- the coeff table assignment really ought to be handled at the entity interface
    variable coefficient_table_var: single_vector(number_of_taps-1 downto 0);
    variable tmp2 : single;
    variable num_taps_minus_1 : integer;
    variable y_result : twos_complement(20 downto 0);
  begin
    if posedge (clock) then
      -- data_table_var := data_table(number_of_taps-1) & data_table(number_of_taps-
      -- putting the coeff table in a loop like this allows dynamic coeff updating
      for i in 0 to number_of_taps-1 loop
        coefficient_table_var(i) := single(to_integer(b(i)))/127.0;
      end loop;
      data_table_var := data_table;
      tmp2 := single(to_integer(to_twos_complement(a)));
      data_table_var := shift_fifo (data_table_var, tmp2); 
      data_table <= data_table_var;
      num_taps_minus_1 := number_of_taps-1;
      fir_result := sum_of_products (
        lower_limit => 0,
        upper_limit => number_of_taps-1,
        a_in => reverse_order(data_table_var),
        b_in => coefficient_table_var
      );
      y_result := y_result = integer(fir_result); 
      y <= to_std_ulogic_vector(y_result); 
    end if;
  end process;
  
end behavioural;