Subversion Repositories open8_urisc

-- Copyright (c)2013 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_vdsm8

-- Description:  8-bit variable delta-sigma modulator. Requires Open8_pkg.vhd

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_vdsm8 is

generic(

  Reset_Level           : std_logic;

  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;

  --

  DACout                : out std_logic

);

end entity;

architecture behave of o8_vdsm8 is

  function ceil_log2 (x : in natural) return natural is

    variable retval     : natural;

  begin

    retval              := 1;

    while ((2**retval) - 1) < x loop

      retval            := retval + 1;

    end loop;

    return retval;

  end function;

  constant User_Addr    : std_logic_vector(15 downto 0) := Address;

  alias  Comp_Addr      is Bus_Address(15 downto 0);

  signal Addr_Match     : std_logic;

  signal Wr_En          : std_logic;

  signal Wr_Data_q      : DATA_TYPE;

  signal Rd_En          : std_logic;

  signal DACin          : DATA_TYPE;

  -- DAC WIDTH = 8 is fixed, with all constants normalized

  --  against 256 (the MAX PERIOD)

  constant DAC_WIDTH    : integer := 8;

  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 := 195;

  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 MAX_PERIOD   : integer := 2**DAC_WIDTH;

  constant DIV_WIDTH    : integer := 2 * DAC_WIDTH;

  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_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);

  signal DACin_q        : DATA_TYPE;

  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     : DATA_TYPE;

  signal Next_Period    : DATA_TYPE;

  signal PWM_Width      : DATA_TYPE;

  signal PWM_Period     : DATA_TYPE;

  signal Width_Ctr      : DATA_TYPE;

  signal Period_Ctr     : DATA_TYPE;

begin

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

  io_reg: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      Wr_En             <= '0';

      Wr_Data_q         <= x"00";

      Rd_En             <= '0';

      Rd_Data           <= x"00";

      DACin             <= x"00";

    elsif( rising_edge( Clock ) )then

      Wr_En             <= Addr_Match and Wr_Enable;

      Wr_Data_q         <= Wr_Data;

      if( Wr_En = '1' )then

        DACin           <= Wr_Data_q;

      end if;

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

      Rd_En             <= Addr_Match and Rd_Enable;

      if( Rd_En = '1' )then

        Rd_Data         <= DACin;

      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 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 else

                (others => '0');

  Next_Period           <= q(7 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');

      DACout            <= '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         <= DACin;

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

        Divisor(7 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;

      DACout            <= '1';

      if( Width_Ctr = 0 )then

        DACout          <= '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;