Subversion Repositories open8_urisc

-- Copyright (c)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 Entity: pwm_adc

-- Description: Integrates a PWM input to return the approximate duty cycle

--              Uses a 1kB block ram as storage for a rolling integrator that

--               acts as a simple successive-approximation ADC.

--

-- Revision History

-- Author          Date     Change

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

-- Seth Henry      05/07/20 Design Start

library ieee;

  use ieee.std_logic_1164.all;

  use ieee.std_logic_unsigned.all;

library work;

  use work.open8_pkg.all;

entity o8_pwm_adc is

generic(

  Address                    : ADDRESS_TYPE

);

port(

  Open8_Bus                  : in  OPEN8_BUS_TYPE;

  Rd_Data                    : out DATA_TYPE;

  --

  PWM_In                     : in  std_logic

);

end entity;

architecture behave of o8_pwm_adc is

  alias Clock                is Open8_Bus.Clock;

  alias Reset                is Open8_Bus.Reset;

  alias uSec_Tick            is Open8_Bus.uSec_Tick;

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

  alias  Comp_Addr           is Open8_Bus.Address(15 downto 0);

  signal Addr_Match          : std_logic := '0';

  signal Rd_En_d             : std_logic := '0';

  signal Rd_En_q             : std_logic := '0';

  signal Sample              : DATA_TYPE := x"00";

  signal RAM_Addr            : std_logic_vector(9 downto 0) := (others => '0');

  signal RAM_Data            : DATA_TYPE := x"00";

  signal Accumulator         : std_logic_vector(17 downto 0) := (others => '0');

  signal Average             : DATA_TYPE := x"00";

begin

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

  Rd_En_d                    <= Addr_Match and Open8_Bus.Rd_En;

  io_reg: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      Rd_En_q                <= '0';

      Rd_Data                <= OPEN8_NULLBUS;

    elsif( rising_edge( Clock ) )then

      Rd_En_q                <= Rd_En_d;

      Rd_Data                <= OPEN8_NULLBUS;

      if( Rd_En_q = '1' )then

        Rd_Data              <= Average;

      end if;

    end if;

  end process;

  -- PWM input is binary, so the sample swings between 0x00 and 0xFF

  Sample                     <= (others => PWM_In);

  U_DP : entity work.o8_pwm_adc_ram

  port map(

                address                  => RAM_Addr,

                clock                    => Clock,

                data                     => Sample,

                wren                     => '1',

                q                        => RAM_Data

        );

  ADC_proc: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

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

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

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

    elsif( rising_edge(Clock) )then

      RAM_Addr               <= RAM_Addr + 1;

      Accumulator            <= Accumulator + ("0000000000" & RAM_Data);

      if( RAM_Addr = 0 )then

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

        Average              <= Accumulator(17 downto 10);

      end if;

    end if;

  end process;

end architecture;