Subversion Repositories t48

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--

-- The Timer/Counter unit.

--

-- $Id: timer.vhd,v 1.5 2004-07-11 16:51:33 arniml Exp $

--

-- Copyright (c) 2004, Arnim Laeuger (arniml@opencores.org)

--

-- All rights reserved

--

-- Redistribution and use in source and synthezised forms, with or without

-- modification, are permitted provided that the following conditions are met:

--

-- Redistributions of source code must retain the above copyright notice,

-- this list of conditions and the following disclaimer.

--

-- Redistributions in synthesized form must reproduce the above copyright

-- notice, this list of conditions and the following disclaimer in the

-- documentation and/or other materials provided with the distribution.

--

-- Neither the name of the author nor the names of other contributors may

-- be used to endorse or promote products derived from this software without

-- specific prior written permission.

--

-- THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"

-- AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,

-- THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

-- PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE

-- LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR

-- CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF

-- SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS

-- INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN

-- CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)

-- ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE

-- POSSIBILITY OF SUCH DAMAGE.

--

-- Please report bugs to the author, but before you do so, please

-- make sure that this is not a derivative work and that

-- you have the latest version of this file.

--

-- The latest version of this file can be found at:

--      http://www.opencores.org/cvsweb.shtml/t48/

--

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

library ieee;

use ieee.std_logic_1164.all;

use work.t48_pack.word_t;

use work.t48_pack.mstate_t;

entity timer is

  generic (

    -- state in which T1 is sampled (3 or 4)

    sample_t1_state_g : integer := 4

  );

  port (

    -- Global Interface -------------------------------------------------------

    clk_i         : in  std_logic;

    res_i         : in  std_logic;

    en_clk_i      : in  boolean;

    t1_i          : in  std_logic;

    clk_mstate_i  : in  mstate_t;

    -- T48 Bus Interface ------------------------------------------------------

    data_i        : in  word_t;

    data_o        : out word_t;

    read_timer_i  : in  boolean;

    write_timer_i : in  boolean;

    -- Decoder Interface ------------------------------------------------------

    start_t_i     : in  boolean;

    start_cnt_i   : in  boolean;

    stop_tcnt_i   : in  boolean;

    overflow_o    : out std_logic

  );

end timer;

library ieee;

use ieee.numeric_std.all;

use work.t48_pack.all;

architecture rtl of timer is

  -- the 8 bit counter core

  signal counter_q   : unsigned(word_t'range);

  signal overflow_q  : boolean;

  -- increment signal for the counter core

  type   inc_type_t is (NONE, TIMER, COUNTER);

  signal increment_s : boolean;

  signal inc_sel_q   : inc_type_t;

  -- T1 edge detector

  signal t1_q        : std_logic;

  signal t1_inc_s    : boolean;

  -- timer prescaler

  signal prescaler_q : unsigned(4 downto 0);

  signal pre_inc_s   : boolean;

begin

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

  -- Verify the generics

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

  -- pragma translate_off

  assert (sample_t1_state_g = 3) or (sample_t1_state_g = 4)

    report "sample_t1_state_g must be either 3 or 4!"

    severity failure;

  -- pragma translate_on

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

  -- Process t1_edge

  --

  -- Purpose:

  --   Implements the edge detector for T1.

  --

  t1_edge: process (t1_i,

                    t1_q,

                    clk_mstate_i)

  begin

    t1_inc_s     <= false;

    -- sample in state according to generic

    -- Old devices: sample at the beginning of state 3

    -- New devices: sample in state 4

    if (sample_t1_state_g = 3 and clk_mstate_i = MSTATE3) or

       (sample_t1_state_g = 4 and clk_mstate_i = MSTATE4) then

      -- detect falling edge

      if t1_q = '1' and t1_i = '0' then

        t1_inc_s <= true;

      end if;

    end if;

  end process t1_edge;

  --

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

  pre_inc_s <= clk_mstate_i = MSTATE4 and prescaler_q = 31;

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

  -- Process inc_sel

  --

  -- Purpose:

  --   Select increment source (timer, counter or none).

  --

  inc_sel: process (inc_sel_q,

                    pre_inc_s,

                    t1_inc_s)

  begin

    -- default assignment

    increment_s     <= false;

    case inc_sel_q is

      when NONE =>

        increment_s <= false;

      when TIMER =>

        increment_s <= pre_inc_s;

      when COUNTER =>

        increment_s <= t1_inc_s;

      when others =>

        null;

    end case;

  end process inc_sel;

  --

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

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

  -- Process regs

  --

  -- Purpose:

  --   Implements the counter, the prescaler and other registers.

  --

  regs: process (res_i, clk_i)

  begin

    if res_i = res_active_c then

      overflow_q     <= false;

      t1_q           <= '0';

      prescaler_q    <= (others => '0');

      inc_sel_q      <= NONE;

    elsif clk_i'event and clk_i = clk_active_c then

      if en_clk_i then

        -- Counter Core and overflow ------------------------------------------

        overflow_q     <= false;

        if write_timer_i then

          counter_q    <= unsigned(data_i);

        elsif increment_s then

          counter_q    <= counter_q + 1;

          if counter_q = 255 then

            overflow_q <= true;

          end if;

        end if;

        -- T1 edge detector ---------------------------------------------------

        if (sample_t1_state_g = 3 and clk_mstate_i = MSTATE3) or

           (sample_t1_state_g = 4 and clk_mstate_i = MSTATE4) then

          t1_q <= t1_i;

        end if;

        -- Prescaler ----------------------------------------------------------

        if start_t_i then

          prescaler_q  <= (others => '0');

        elsif clk_mstate_i = MSTATE3 then

          prescaler_q  <= prescaler_q + 1;

        end if;

        -- Increment Selector -------------------------------------------------

        if start_t_i then

          inc_sel_q <= TIMER;

        elsif start_cnt_i then

          inc_sel_q <= COUNTER;

        elsif stop_tcnt_i then

          inc_sel_q <= NONE;

        end if;

      end if;

    end if;

  end process regs;

  --

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

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

  -- Output Mapping.

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

  data_o     <=   std_logic_vector(counter_q)

                when read_timer_i else

                  (others => bus_idle_level_c);

  overflow_o <= to_stdLogic(overflow_q);

end rtl;

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

-- File History:

--

-- $Log: not supported by cvs2svn $

-- Revision 1.4  2004/07/04 13:06:45  arniml

-- counter_q is not cleared during reset

-- this would match all different descriptions of the Counter as

-- a) if the software assumes that the Counter is modified during reset, it

--    will initialize the Counter anyhow

-- b) the special case 'Counter not modified during reset' is covered

--

-- Revision 1.3  2004/05/16 15:32:57  arniml

-- fix edge detector bug for counter

--

-- Revision 1.2  2004/04/15 22:05:13  arniml

-- increment prescaler with MSTATE4

--

-- Revision 1.1  2004/03/23 21:31:53  arniml

-- initial check-in

--

--

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