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-- Copyright (c)2013, 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

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-- (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 : ltc2355_2p

-- Description: Reads out a pair of LTC2355 14-bit ADCs which are wired with

--            :  common clock and CONVERT START inputs. Because they are

--            :  synchronized, this entity provides simultaneously updated

--            :  parallel data buses.

--

-- Notes      : Depends on the fact that the two LTC2355 converters are wired

--            :  with their SCLK and CONV lines tied together, and DATA1 and

--            :  DATA2 independently routed to separate I/O pins.

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

use ieee.std_logic_arith.all;

use ieee.std_logic_misc.all;

library work;

  use work.open8_pkg.all;

entity o8_ltc2355_2p is

generic(

  Address                    : ADDRESS_TYPE;

  Reset_Level                : std_logic;

  Sys_Freq                   : real

);

port(

  Clock                      : in  std_logic; -- 96MHz MAX for proper operation

  Reset                      : in  std_logic;

  uSec_Tick                  : in  std_logic;

  -- Client IF

  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;

  Interrupt                  : out std_logic;

  -- ADC IF

  ADC_SCLK                   : out std_logic;

  ADC_CONV                   : out std_logic;

  ADC_DATA1                  : in  std_logic;

  ADC_DATA2                  : in  std_logic

);

end entity;

architecture behave of o8_ltc2355_2p is

  constant Divide_SCLK_by_2  : boolean := (Sys_Freq > 96000000.0);

  constant User_Addr         : std_logic_vector(15 downto 3) := Address(15 downto 3);

  alias  Comp_Addr           is Bus_Address(15 downto 3);

  alias  Reg_Sel             is Bus_Address(2 downto 0);

  signal Reg_Sel_q           : std_logic_vector(2 downto 0);

  signal Wr_Data_q           : DATA_TYPE;

  signal Addr_Match          : std_logic;

  signal Wr_En               : std_logic;

  signal Rd_En               : std_logic;

  signal User_In             : DATA_TYPE;

  signal User_Trig           : std_logic;

  signal Timer_Int           : DATA_TYPE;

  signal Timer_Cnt           : DATA_TYPE;

  signal Timer_Trig          : std_logic;

  type ADC_STATES is ( IDLE, START, CLK_HIGH, CLK_HIGH2, CLK_LOW, CLK_LOW2, UPDATE );

  signal ad_state            : ADC_STATES;

  signal rx_buffer1          : std_logic_vector(16 downto 0);

  signal rx_buffer2          : std_logic_vector(16 downto 0);

  signal bit_cntr            : std_logic_vector(4 downto 0);

  constant BIT_COUNT         : std_logic_vector(4 downto 0) :=

                                conv_std_logic_vector(16,5);

  signal ADC1_Data           : std_logic_vector(13 downto 0);

  signal ADC2_Data           : std_logic_vector(13 downto 0);

  signal ADC_Ready           : std_logic;

begin

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

  io_reg: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

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

      Wr_Data_q              <= x"00";

      Wr_En                  <= '0';

      Rd_En                  <= '0';

      Rd_Data                <= OPEN8_NULLBUS;

      User_Trig              <= '0';

      Timer_Int              <= x"00";

    elsif( rising_edge( Clock ) )then

      Reg_Sel_q              <= Reg_Sel;

      Wr_Data_q              <= Wr_Data;

      Wr_En                  <= Wr_Enable and Addr_Match;

      User_Trig              <= '0';

      if( Wr_En = '1' )then

        if( Reg_Sel_q = "110" )then

          Timer_Int          <= Wr_Data_q;

        end if;

        if( Reg_Sel_q = "111" )then

          User_Trig          <= '1';

        end if;

      end if;

      Rd_En                  <= Rd_Enable and Addr_Match;

      Rd_Data                <= OPEN8_NULLBUS;

      if( Rd_En = '1' )then

        case( Reg_Sel_q )is

          -- Channel 1, Full resolution, lower byte

          when "000" =>

            Rd_Data          <= ADC1_Data(7 downto 0);

          -- Channel 1, Full resolution, upper byte

          when "001" =>

            Rd_Data          <= "00" & ADC1_Data(13 downto 8);

          -- Channel 2, Full resolution, lower byte

          when "010" =>

            Rd_Data          <= ADC2_Data(7 downto 0);

          -- Channel 2, Full resolution, upper byte

          when "011" =>

            Rd_Data          <= "00" & ADC2_Data(13 downto 8);

          -- Channel 1, 8-bit resolution

          when "100" =>

            Rd_Data          <= ADC1_Data(13 downto 6);

          -- Channel 2, 8-bit resolution

          when "101" =>

            Rd_Data          <= ADC2_Data(13 downto 6);

          -- Self-update rate

          when "110" =>

            Rd_Data          <= Timer_Int;

          -- Interface status

          when "111" =>

            Rd_Data(7)       <= ADC_Ready;

          when others =>

            null;

        end case;

      end if;

    end if;

  end process;

  Interval_proc: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      Timer_Cnt              <= x"00";

      Timer_Trig             <= '0';

    elsif( rising_edge(Clock) )then

      Timer_Trig             <= '0';

      Timer_Cnt              <= Timer_Cnt - uSec_Tick;

      if( or_reduce(Timer_Cnt) = '0' )then

        Timer_Cnt            <= Timer_Int;

        Timer_Trig           <= or_reduce(Timer_Int); -- Only issue output on Int > 0

      end if;

    end if;

  end process;

  ADC_IO_FSM: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      ad_state               <= IDLE;

      ADC_Ready              <= '0';

      rx_buffer1             <= (others => '0');

      rx_buffer2             <= (others => '0');

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

      ADC1_Data              <= (others => '0');

      ADC2_Data              <= (others => '0');

      ADC_SCLK               <= '1';

      ADC_CONV               <= '0';

      Interrupt              <= '0';

    elsif( rising_edge(Clock) )then

      ADC_Ready              <= '0';

      ADC_SCLK               <= '1';

      ADC_CONV               <= '0';

      Interrupt              <= '0';

      case( ad_state )is

        when IDLE =>

          ADC_Ready          <= '1';

          if( (User_Trig or Timer_Trig) = '1' )then

            ad_state         <= START;

          end if;

        when START =>

          ADC_SCLK           <= '0';

          ADC_CONV           <= '1';

          bit_cntr           <= BIT_COUNT;

          ad_state           <= CLK_HIGH;

        when CLK_HIGH =>

          ad_state           <= CLK_LOW;

          if( Divide_SCLK_by_2 )then

            ad_state         <= CLK_HIGH2;

          end if;

        when CLK_HIGH2 =>

          ad_state           <= CLK_LOW;

        when CLK_LOW =>

          ADC_SCLK           <= '0';

          rx_buffer1(conv_integer(bit_cntr)) <= ADC_DATA1;

          rx_buffer2(conv_integer(bit_cntr)) <= ADC_DATA2;

          bit_cntr           <= bit_cntr - 1;

          ad_state           <= CLK_HIGH;

          if( bit_cntr = 0 )then

            ad_state         <= UPDATE;

          elsif( Divide_SCLK_by_2 )then

            ad_state         <= CLK_LOW2;

          end if;

        when CLK_LOW2 =>

          ADC_SCLK           <= '0';

          ad_state           <= CLK_HIGH;

        when UPDATE =>

          ADC_SCLK           <= '0';

          ad_state           <= IDLE;

          ADC1_Data          <= rx_buffer1(14 downto 1);

          ADC2_Data          <= rx_buffer2(14 downto 1);

          Interrupt          <= '1';

        when others =>

          null;

      end case;

    end if;

  end process;

end architecture;