system/ip/audio_single_pwm_1.0/hdl/pulse_gen.vhdl

   1 --
   2 -- * pulse generator *
   3 --
   4 -- based on code from LXPWR motion control board (c) PiKRON Ltd
   5 -- idea by Pavel Pisa PiKRON Ltd <ppisa@pikron.com>
   6 --
   7 -- license: BSD
   8 --
   9
  10 library ieee;
  11 use ieee.std_logic_1164.all;
  12 use ieee.numeric_std.all;
  13
  14 entity pulse_gen is
  15         generic (
  16                 duration_width_g : natural := 4
  17         );
  18         port
  19         (
  20                 clk_i      : in std_logic;                              --clk to divide
  21                 en_i       : in std_logic;                              --enable bit?
  22                 reset_i    : in std_logic;                              --asynch. reset
  23                 trigger_i  : in std_logic;                              --start to generate pulse
  24                 duration_i : in std_logic_vector(duration_width_g-1 downto 0);--duration/interval of the pulse
  25                 q_out_o    : out std_logic                              --generates pulse for given duration
  26         );
  27 end pulse_gen;
  28
  29 architecture behavioral of pulse_gen is
  30         signal cnt_val_s : natural range 0 to (2**duration_width_g - 1);        --counter value before DFF
  31         signal cnt_val_r : natural range 0 to (2**duration_width_g - 1);        --counter value after DFF
  32 begin
  33
  34 comb: process (reset_i, en_i, duration_i, trigger_i, cnt_val_r)
  35         begin
  36                 if reset_i = '1' then --reset detection
  37                         cnt_val_s <= 0;         --set defined value
  38                         q_out_o   <= '0';                               --reset output
  39                 else
  40                         if en_i = '0' then                              --stop-state
  41                                 cnt_val_s <= cnt_val_r;                 --hold the value
  42                         else
  43                                 if trigger_i = '1' then                 --trigger pulse generator
  44                                         if to_integer(unsigned(duration_i)) = 0 then
  45                                                 q_out_o   <= '0';
  46                                         else
  47                                                 q_out_o   <= '1';
  48                                         end if;
  49                                         cnt_val_s <= to_integer(unsigned(duration_i)); --set initial value
  50                                 elsif cnt_val_r = 0 then                        --pulse finished
  51                                         cnt_val_s <= cnt_val_r;
  52                                         q_out_o   <= '0';               --set output
  53                                 else
  54                                         cnt_val_s <= cnt_val_r - 1;     --decrement counter
  55                                         q_out_o   <= '1';               --reset output
  56                                 end if;
  57                         end if;
  58                 end if;
  59         end process;
  60
  61 seq: process
  62         begin
  63                 wait until clk_i'event and clk_i = '1';
  64                 cnt_val_r <= cnt_val_s;
  65         end process;
  66
  67 end behavioral;
  68