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-- Baud Rate Counter                                                          --

--------------------------------------------------------------------------------

-- Copyright (C)2011  Mathias Hörtnagl <mathias.hoertnagl@gmail.comt>         --

--                                                                            --

-- This program is free software: you can redistribute it and/or modify       --

-- it under the terms of the GNU General Public License as published by       --

-- the Free Software Foundation, either version 3 of the License, or          --

-- (at your option) any later version.                                        --

--                                                                            --

-- This program is distributed in the hope that it will be useful,            --

-- but WITHOUT ANY WARRANTY; without even the implied warranty of             --

-- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the              --

-- GNU General Public License for more details.                               --

--                                                                            --

-- You should have received a copy of the GNU General Public License          --

-- along with this program.  If not, see <http://www.gnu.org/licenses/>.      --

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library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

entity counter is

   generic(

      FREQ : positive := 50;           -- Clock frequency in MHz.

      RATE : positive := 19200         -- Baud rate (times sampling rate).

   );

   port(

      clk    : in  std_logic;

      rst    : in  std_logic;

      tick   : out std_logic

   );

end counter;

architecture rtl of counter is

   constant MAX : positive := (FREQ*1000000)/(RATE*16);

   signal c, cin : natural range 0 to MAX;

begin

   tick <= '1' when c = MAX else '0';

   cin  <=  0  when c = MAX else c + 1;

   reg : process (clk)

   begin

      if rising_edge(clk) then

         if rst = '1' then

            c <= 0;

         else

            c <= cin;

         end if;

      end if;

   end process;

end rtl;