Subversion Repositories pwm_with_dithering

----------------------------------------------------------------------------------
-- Company: 		 Aboa Space Research Oy (ASRO)
-- Engineer: 		 Tero Säntti
-- 
-- Create Date:    11:43:23 02/03/2021 
-- Design Name: 	 PWM
-- Module Name:    pwm_pipelined_small - Behavioral 
-- Target Devices: None / non-specific
-- Tool versions:  None / non-specific
-- Description: 	 Dithered PWM with pipelining to increase maximum clock 
--						 frequency. Somewhat larger and added latency during input
--						 changes. Not sensitive to input changes during operation.
--						 Modified by removing one register (target_i) to give smaller
--						 size with slight speed trade-off.
--
-- Revision: 
-- Revision 0.01 - File Created
-- Additional Comments: 
--
----------------------------------------------------------------------------------
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.NUMERIC_STD.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;  
 
entity pwm_pipelined_small is
    Generic ( 
				bits: integer:=16;
				dithering:integer:=5
				);
    Port ( clk : in  STD_LOGIC;
           set : in  STD_LOGIC_VECTOR(bits-1 downto 0);
           o   : out  STD_LOGIC);
end pwm_pipelined_small;
 
architecture Behavioral of pwm_pipelined_small is
signal o_i:std_logic:='0';
signal cnt:std_logic_vector(bits-1 downto 0):=(others => '0');
signal zeros:std_logic_vector((bits-dithering)-1 downto 0):=(others => '0');
signal ones:std_logic_vector((bits-dithering)-1 downto 0):=(others => '1');
signal target:std_logic_vector((bits-dithering) downto 0);
signal reversed_cnt_top:std_logic_vector((dithering)-1 downto 0);
signal inc:std_logic;
signal trigger:std_logic;
 
function reverse_and_rebase_bit_order(a: in std_logic_vector)
return std_logic_vector is
  variable result: std_logic_vector(a'high-a'low downto 0);
begin
  for i in a'RANGE loop
    result(a'high-i) := a(i);
  end loop;
  return result;
end;
 
begin
 
-- output mapping:
o <= o_i;
 
normal: if dithering = 0  generate
 
zeros <= (others => '0');
ones  <= (others => '1');
 
doit:process(clk)
begin
if rising_edge(clk) then
	cnt <= cnt + 1;
	o_i <= o_i;
	trigger <= '0';
	if trigger = '1' then o_i <= '1'; end if;
	if '0' & cnt=target then o_i <= '0'; end if;
	if cnt(bits-1 downto 0) = ones then target <= '0' & set; trigger <= '1'; end if;
end if;
end process;
end generate;
 
dithered: if dithering > 0  generate
 
reversed_cnt_top <= reverse_and_rebase_bit_order(cnt(bits-1 downto bits-dithering));
 
doit:process(clk)
begin
if rising_edge(clk) then
	if (reversed_cnt_top < set(dithering-1 downto 0)) then inc <= '1'; else inc <= '0'; end if;
	cnt <= cnt + 1;
	o_i <= o_i;
	trigger <= '0';
	if trigger = '1' then o_i <= '1'; end if;
	if ('0' & cnt((bits-dithering)-1 downto 0)) = target then o_i <= '0'; end if;
	if cnt((bits-dithering)-1 downto 0) = ones then target <= ('0' & set(bits-1 downto dithering)) + inc; trigger <= '1'; end if;
end if;
end process;
end generate;
 
end Behavioral;