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-- Copyright (c)2019, 2020 Jeremy Seth Henry

-- All rights reserved.

--

-- Redistribution and use in source and binary 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 binary 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,

--       where applicable (as part of a user interface, debugging port, etc.)

--

-- THIS SOFTWARE IS PROVIDED BY JEREMY SETH HENRY ``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 JEREMY SETH HENRY 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.

--

-- VHDL Units :  o8_vdsm12

-- Description:  12-bit variable delta-sigma modulator. Requires Open8_pkg.vhd

--

-- Register Map:

-- Offset  Bitfield Description                        Read/Write

--   0x0   AAAAAAAA Pending DAC Level (7:0)            (R/W)

--   0x1   AAAAAAAA Pending DAC Level (11:8)           (R/W)

--   0x2   -------- Clear DAC Output (on write)        (WO)

--   0x3   AAAAAAAA Update DAC Output (on write)       (RO)

--

-- Revision History

-- Author          Date     Change

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

-- Seth Henry      12/18/19 Design start

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

use ieee.std_logic_arith.all;

library work;

  use work.open8_pkg.all;

entity o8_vdsm12 is

generic(

  Reset_Level           : std_logic := '1';

  Address               : ADDRESS_TYPE

);

port(

  Clock                 : in  std_logic;

  Reset                 : in  std_logic;

  --

  Bus_Address           : in  ADDRESS_TYPE;

  Wr_Enable             : in  std_logic;

  Wr_Data               : in  DATA_TYPE;

  Rd_Enable             : in  std_logic;

  Rd_Data               : out DATA_TYPE;

  --

  PDM_Out               : out std_logic

);

end entity;

architecture behave of o8_vdsm12 is

  constant User_Addr    : std_logic_vector(15 downto 2)

                          := Address(15 downto 2);

  alias  Comp_Addr      is Bus_Address(15 downto 2);

  alias  Reg_Addr       is Bus_Address(1 downto 0);

  signal Reg_Sel        : std_logic_vector(1 downto 0);

  signal Addr_Match     : std_logic;

  signal Wr_En          : std_logic;

  signal Wr_Data_q      : DATA_TYPE;

  signal Rd_En          : std_logic;

  constant DAC_Width    : integer := 12;

  signal DAC_Val_LB     : DATA_TYPE;

  signal DAC_Val_UB     : DATA_TYPE;

  signal DAC_Val        : std_logic_vector(DAC_Width-1 downto 0);

  constant DELTA_1_I    : integer := 1;

  constant DELTA_2_I    : integer := 5;

  constant DELTA_3_I    : integer := 25;

  constant DELTA_4_I    : integer := 75;

  constant DELTA_5_I    : integer := 125;

  constant DELTA_6_I    : integer := 250;

  constant DELTA_7_I    : integer := 500;

  constant DELTA_8_I    : integer := 1000;

  constant DELTA_9_I    : integer := 2000;

  constant DELTA_10_I   : integer := 3000;

  constant DELTA_1      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_1_I, DAC_Width);

  constant DELTA_2      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_2_I, DAC_Width);

  constant DELTA_3      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_3_I, DAC_Width);

  constant DELTA_4      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_4_I, DAC_Width);

  constant DELTA_5      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_5_I, DAC_Width);

  constant DELTA_6      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_6_I, DAC_Width);

  constant DELTA_7      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_7_I, DAC_Width);

  constant DELTA_8      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_8_I, DAC_Width);

  constant DELTA_9      : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_9_I, DAC_Width);

  constant DELTA_10     : std_logic_vector(DAC_Width-1 downto 0) :=

                           conv_std_logic_vector(DELTA_10_I, DAC_Width);

  constant MAX_PERIOD   : integer := 2**DAC_Width;

  constant DIV_WIDTH    : integer := DAC_Width * 2;

  constant PADJ_1_I     : integer := DELTA_1_I * MAX_PERIOD;

  constant PADJ_2_I     : integer := DELTA_2_I * MAX_PERIOD;

  constant PADJ_3_I     : integer := DELTA_3_I * MAX_PERIOD;

  constant PADJ_4_I     : integer := DELTA_4_I * MAX_PERIOD;

  constant PADJ_5_I     : integer := DELTA_5_I * MAX_PERIOD;

  constant PADJ_6_I     : integer := DELTA_6_I * MAX_PERIOD;

  constant PADJ_7_I     : integer := DELTA_7_I * MAX_PERIOD;

  constant PADJ_8_I     : integer := DELTA_8_I * MAX_PERIOD;

  constant PADJ_9_I     : integer := DELTA_9_I * MAX_PERIOD;

  constant PADJ_10_I    : integer := DELTA_10_I * MAX_PERIOD;

  constant PADJ_1       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_1_I,DIV_WIDTH);

  constant PADJ_2       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_2_I,DIV_WIDTH);

  constant PADJ_3       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_3_I,DIV_WIDTH);

  constant PADJ_4       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_4_I,DIV_WIDTH);

  constant PADJ_5       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_5_I,DIV_WIDTH);

  constant PADJ_6       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_6_I,DIV_WIDTH);

  constant PADJ_7       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_7_I,DIV_WIDTH);

  constant PADJ_8       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_8_I,DIV_WIDTH);

  constant PADJ_9       : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_9_I,DIV_WIDTH);

  constant PADJ_10      : std_logic_vector(DIV_WIDTH-1 downto 0) :=

                           conv_std_logic_vector(PADJ_10_I,DIV_WIDTH);

  signal DACin_q        : std_logic_vector(DAC_Width-1 downto 0);

  signal Divisor        : std_logic_vector(DIV_WIDTH-1 downto 0);

  signal Dividend       : std_logic_vector(DIV_WIDTH-1 downto 0);

  signal q              : std_logic_vector(DIV_WIDTH*2-1 downto 0);

  signal diff           : std_logic_vector(DIV_WIDTH downto 0);

  constant CB           : integer := ceil_log2(DIV_WIDTH);

  signal count          : std_logic_vector(CB-1 downto 0);

  signal Next_Width     : std_logic_vector(DAC_Width-1 downto 0);

  signal Next_Period    : std_logic_vector(DAC_Width-1 downto 0);

  signal PWM_Width      : std_logic_vector(DAC_Width-1 downto 0);

  signal PWM_Period     : std_logic_vector(DAC_Width-1 downto 0);

  signal Width_Ctr      : std_logic_vector(DAC_Width-1 downto 0);

  signal Period_Ctr     : std_logic_vector(DAC_Width-1 downto 0);

begin

  Addr_Match            <= '1' when Comp_Addr = User_Addr else '0';

  io_reg: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      Reg_Sel           <= "00";

      Rd_En             <= '0';

      Rd_Data           <= OPEN8_NULLBUS;

      Wr_En             <= '0';

      Wr_Data_q         <= x"00";

      DAC_Val_LB        <= x"00";

      DAC_Val_UB        <= x"00";

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

    elsif( rising_edge( Clock ) )then

      Reg_Sel           <= Reg_Addr;

      Wr_En             <= Addr_Match and Wr_Enable;

      Wr_Data_q         <= Wr_Data;

      if( Wr_En = '1' )then

        case( Reg_Sel )is

          when "00" =>

            DAC_Val_LB  <= Wr_Data_q;

          when "01" =>

            DAC_Val_UB  <= "0000" & Wr_Data_q(3 downto 0);

          when "10" =>

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

          when "11" =>

            DAC_Val     <= DAC_Val_UB(3 downto 0) & DAC_Val_LB;

          when others => null;

        end case;

      end if;

      Rd_Data           <= OPEN8_NULLBUS;

      Rd_En             <= Addr_Match and Rd_Enable;

      if( Rd_En = '1' )then

        case( Reg_Sel )is

          when "00" =>

            Rd_Data     <= DAC_Val_LB;

          when "01" =>

            Rd_Data     <= DAC_Val_UB;

          when others => null;

        end case;

      end if;

    end if;

  end process;

  diff                  <= ('0' & q(DIV_WIDTH*2-2 downto DIV_WIDTH-1)) -

                           ('0' & Divisor);

  Dividend   <= PADJ_2  when DACin_q >= DELTA_2_I and DACin_q < DELTA_3_I else

                PADJ_3  when DACin_q >= DELTA_3_I and DACin_q < DELTA_4_I else

                PADJ_4  when DACin_q >= DELTA_4_I and DACin_q < DELTA_5_I else

                PADJ_5  when DACin_q >= DELTA_5_I and DACin_q < DELTA_6_I else

                PADJ_6  when DACin_q >= DELTA_6_I and DACin_q < DELTA_7_I else

                PADJ_7  when DACin_q >= DELTA_7_I and DACin_q < DELTA_8_I else

                PADJ_8  when DACin_q >= DELTA_8_I and DACin_q < DELTA_9_I else

                PADJ_9  when DACin_q >= DELTA_9_I and DACin_q < DELTA_10_I else

                PADJ_10 when DACin_q >= DELTA_10_I else

                PADJ_1;

  Next_Width <= DELTA_1  when DACin_q >= DELTA_1_I and DACin_q < DELTA_2_I else

                DELTA_2  when DACin_q >= DELTA_2_I and DACin_q < DELTA_3_I else

                DELTA_3  when DACin_q >= DELTA_3_I and DACin_q < DELTA_4_I else

                DELTA_4  when DACin_q >= DELTA_4_I and DACin_q < DELTA_5_I else

                DELTA_5  when DACin_q >= DELTA_5_I and DACin_q < DELTA_6_I else

                DELTA_6  when DACin_q >= DELTA_6_I and DACin_q < DELTA_7_I else

                DELTA_7  when DACin_q >= DELTA_7_I and DACin_q < DELTA_8_I else

                DELTA_8  when DACin_q >= DELTA_8_I and DACin_q < DELTA_9_I else

                DELTA_9  when DACin_q >= DELTA_9_I and DACin_q < DELTA_10_I else

                DELTA_10 when DACin_q >= DELTA_10_I else

                (others => '0');

  Next_Period            <= q(DAC_Width-1 downto 0) - 1;

  vDSM_proc: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

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

      count             <= (others => '1');

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

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

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

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

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

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

      PDM_Out           <= '0';

    elsif( rising_edge(Clock) )then

      q                 <= diff(DIV_WIDTH-1 downto 0) &

                           q(DIV_WIDTH-2 downto 0) & '1';

      if( diff(DIV_WIDTH) = '1' )then

        q               <= q(DIV_WIDTH*2-2 downto 0) & '0';

      end if;

      count             <= count + 1;

      if( count = DIV_WIDTH )then

        PWM_Width       <= Next_Width;

        PWM_Period      <= Next_Period;

        DACin_q         <= DAC_val;

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

        Divisor(DAC_Width-1 downto 0) <= DACin_q;

        q               <= conv_std_logic_vector(0,DIV_WIDTH) & Dividend;

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

      end if;

      Period_Ctr        <= Period_Ctr - 1;

      Width_Ctr         <= Width_Ctr - 1;

      PDM_Out           <= '1';

      if( Width_Ctr = 0 )then

        PDM_Out         <= '0';

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

      end if;

      if( Period_Ctr = 0 )then

        Period_Ctr      <= PWM_Period;

        Width_Ctr       <= PWM_Width;

      end if;

    end if;

  end process;

end architecture;