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-- $Id: clkdivce.vhd 314 2010-07-09 17:38:41Z mueller $

--

-- Copyright 2007- by Walter F.J. Mueller <W.F.J.Mueller@gsi.de>

--

-- This program is free software; you may redistribute and/or modify it under

-- the terms of the GNU General Public License as published by the Free

-- Software Foundation, either version 2, 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 complete details.

--

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

-- Module Name:    clkgen - syn

-- Description:    Generate usec and msec enable signals

--

-- Dependencies:   -

-- Test bench:     -

-- Target Devices: generic

-- Tool versions:  xst 8.1, 8.2, 9.1, 9.2; ghdl 0.18-0.25

-- Revision History: 

-- Date        Rev  Version    Comment

-- 2008-01-20   112   1.0.2  rename clkgen->clkdivce; remove SYS_CLK port

-- 2007-10-12    88   1.0.1  avoid ieee.std_logic_unsigned, use cast to unsigned

-- 2007-06-30    62   1.0    Initial version 

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_arith.all;

use work.slvtypes.all;

entity clkdivce is                      -- generate usec/msec ce pulses

  generic (

    CDUWIDTH : positive := 6;           -- usec clock divider width

    USECDIV : positive :=  50;          -- divider ratio for usec pulse

    MSECDIV : positive := 1000);        -- divider ratio for msec pulse

  port (

    CLK     : in slbit;                 -- input clock

    CE_USEC : out slbit;                -- usec pulse

    CE_MSEC : out slbit                 -- msec pulse

  );

end clkdivce;

architecture syn of clkdivce is

  type regs_type is record

    ucnt : slv(CDUWIDTH-1 downto 0);    -- usec clock divider counter

    mcnt : slv10;                       -- msec clock divider counter

    usec : slbit;                       -- usec pulse

    msec : slbit;                       -- msec pulse

  end record regs_type;

  constant regs_init : regs_type := (

    conv_std_logic_vector(USECDIV-1,CDUWIDTH),

    conv_std_logic_vector(MSECDIV-1,10),

    '0','0'

  );

  signal R_REGS : regs_type := regs_init;  -- state registers

  signal N_REGS : regs_type := regs_init;  -- next value state regs

begin

  assert USECDIV <= 2**CDUWIDTH and MSECDIV <= 1024

    report "assert(USECDIV <= 2**CDUWIDTH and MSECDIV <= 1024): " &

           "USECDIV too large for given CDUWIDTH or MSECDIV>1024"

    severity FAILURE;

  proc_regs: process (CLK)

  begin

    if CLK'event and CLK='1' then

      R_REGS <= N_REGS;

    end if;

  end process proc_regs;

  proc_next: process (R_REGS)

    variable r : regs_type := regs_init;

    variable n : regs_type := regs_init;

  begin

    r := R_REGS;

    n := R_REGS;

    n.usec := '0';

    n.msec := '0';

    n.ucnt := unsigned(r.ucnt) - 1;

    if unsigned(r.ucnt) = 0 then

      n.usec := '1';

      n.ucnt := conv_std_logic_vector(USECDIV-1,CDUWIDTH);

      n.mcnt := unsigned(r.mcnt) - 1;

      if unsigned(r.mcnt) = 0 then

        n.msec := '1';

        n.mcnt := conv_std_logic_vector(MSECDIV-1,10);

      end if;

    end if;

    N_REGS <= n;

    CE_USEC <= r.usec;

    CE_MSEC <= r.msec;

  end process proc_next;

end syn;