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-- $Id: s6_cmt_sfs_gsim.vhd 799 2016-08-21 09:20:19Z mueller $

--

-- Copyright 2013- 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:    s6_cmt_sfs - sim

-- Description:    Spartan-6 CMT for simple frequency synthesis

--                 simple vhdl model, without Xilinx UNISIM primitives

--

-- Dependencies:   -

-- Test bench:     -

-- Target Devices: generic Spartan-6

-- Tool versions:  xst 14.5-14.7; ghdl 0.29-0.33

--

-- Revision History: 

-- Date         Rev Version  Comment

-- 2016-08-18   799   1.0.1  remove 'assert false' from report statements

-- 2013-10-06   538   1.0    Initial version (derived from s7_cmt_sfs_gsim)

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

library ieee;

use ieee.std_logic_1164.all;

use work.slvtypes.all;

entity s6_cmt_sfs is                    -- Spartan-6 CMT for simple freq. synth.

  generic (

    VCO_DIVIDE : positive := 1;         -- vco clock divide

    VCO_MULTIPLY : positive := 1;       -- vco clock multiply 

    OUT_DIVIDE : positive := 1;         -- output divide

    CLKIN_PERIOD : real := 10.0;        -- CLKIN period (def is 10.0 ns)

    CLKIN_JITTER : real := 0.01;        -- CLKIN jitter (def is 10 ps)

    STARTUP_WAIT : boolean := false;    -- hold FPGA startup till LOCKED

    GEN_TYPE : string := "PLL");        -- PLL or MMCM

  port (

    CLKIN : in slbit;                   -- clock input

    CLKFX : out slbit;                  -- clock output (synthesized freq.) 

    LOCKED : out slbit                  -- pll/mmcm locked

  );

end s6_cmt_sfs;

architecture sim of s6_cmt_sfs is

  signal CLK_DIVPULSE : slbit := '0';

  signal CLKOUT_PERIOD : Delay_length := 0 ns;

  signal R_CLKOUT : slbit := '0';

  signal R_LOCKED : slbit := '0';

begin

  proc_init : process

    -- currently frequency limits taken from Spartan-6 speed grade -2

    constant f_vcomin_pll  : integer :=  400;

    constant f_vcomax_pll  : integer := 1000;

    constant f_pdmin_pll   : integer :=   19;

    constant f_pdmax_pll   : integer :=  375;

    variable t_vco : Delay_length := 0 ns;

    variable t_vcomin : Delay_length := 0 ns;

    variable t_vcomax : Delay_length := 0 ns;

    variable t_pd : Delay_length := 0 ns;

    variable t_pdmin : Delay_length := 0 ns;

    variable t_pdmax : Delay_length := 0 ns;

  begin

    -- validate generics

    if not (GEN_TYPE = "PLL" or GEN_TYPE = "DCM") then

      report "assert(GEN_TYPE='PLL' or GEN_TYPE='DCM')"

        severity failure;

    end if;

    if VCO_DIVIDE/=1 or VCO_MULTIPLY/=1 or OUT_DIVIDE/=1 then

      if GEN_TYPE = "PLL" then

        -- check DIV/MULT parameter range

        if VCO_DIVIDE<1   or VCO_DIVIDE>52 or

           VCO_MULTIPLY<1 or VCO_MULTIPLY>64 or

           OUT_DIVIDE<1   or OUT_DIVIDE>128

        then

          report

          "assert(VCO_DIVIDE in 1:52 VCO_MULTIPLY in 1:64 OUT_DIVIDE in 1:128)"

            severity failure;

        end if;

        -- setup VCO and PD range check boundaries

        t_vcomin := (1000 ns / f_vcomax_pll) - 1 ps;

        t_vcomax := (1000 ns / f_vcomin_pll) + 1 ps;

        t_pdmin  := (1000 ns / f_pdmax_pll) - 1 ps;

        t_pdmax  := (1000 ns / f_pdmin_pll) + 1 ps;

        -- now check whether VCO and PD frequency is in range

        t_pd  := (1 ps * (1000.0*CLKIN_PERIOD)) * VCO_DIVIDE;

        t_vco := t_pd / VCO_MULTIPLY;

        if t_vco<t_vcomin or t_vco>t_vcomax then

          report "assert(VCO frequency out of range)"

            severity failure;

        end if;

        if t_pd<t_pdmin or t_pd>t_pdmax then

          report "assert(PD frequency out of range)"

            severity failure;

        end if;

    end if; -- GEN_TYPE = "PLL"

      if GEN_TYPE = "DCM" then

        -- check DIV/MULT parameter range

        if VCO_DIVIDE<1   or VCO_DIVIDE>32 or

           VCO_MULTIPLY<2 or VCO_MULTIPLY>32 or

           OUT_DIVIDE/=1

        then

          report

          "assert(VCO_DIVIDE in 1:32 VCO_MULTIPLY in 2:32 OUT_DIVIDE=1)"

            severity failure;

        end if;

      end if; -- GEN_TYPE = "MMCM"

    end if;  -- one factor /= 1

    wait;

  end process proc_init;

  proc_clkin : process (CLKIN)

    variable t_lastclkin : time := 0 ns;

    variable t_lastperiod : Delay_length := 0 ns;

    variable t_period : Delay_length := 0 ns;

    variable nclkin : integer := 1;

  begin

    if CLKIN'event then

      if CLKIN = '1' then               -- if CLKIN rising edge

        if t_lastclkin > 0 ns then

          t_lastperiod := t_period;

          t_period := now - t_lastclkin;

          CLKOUT_PERIOD <= (t_period * VCO_DIVIDE * OUT_DIVIDE) / VCO_MULTIPLY;

          if t_lastperiod > 0 ns and abs(t_period-t_lastperiod) > 1 ps then

            report "s6_cmt_sp_sfs: CLKIN unstable" severity warning;

          end if;

        end if;

        t_lastclkin := now;

        if t_period > 0 ns then

          nclkin := nclkin - 1;

          if nclkin <= 0 then

            nclkin := VCO_DIVIDE * OUT_DIVIDE;

            CLK_DIVPULSE <= '1';

            R_LOCKED     <= '1';

          end if;

        end if;

      else                              -- if CLKIN falling edge

        CLK_DIVPULSE <= '0';

      end if;

    end if;

  end process proc_clkin;

  proc_clkout : process

    variable t_lastclkin : time := 0 ns;

    variable t_lastperiod : Delay_length := 0 ns;

    variable t_period : Delay_length := 0 ns;

    variable nclkin : integer := 1;

  begin

    loop

      wait until CLK_DIVPULSE = '1';

      for i in 1 to VCO_MULTIPLY loop

        R_CLKOUT <= '1';

        wait for CLKOUT_PERIOD/2;

        R_CLKOUT <= '0';

        if i /= VCO_MULTIPLY then

          wait for CLKOUT_PERIOD/2;

        end if;

      end loop;  -- i

    end loop;

  end process proc_clkout;

  CLKFX  <= R_CLKOUT;

  LOCKED <= R_LOCKED;

end sim;