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-- Copyright (c)2023 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 : adc12s022
-- Description: Provides higher-level control of a single ADC128S022 12-bit ADC
-- Note that the base part has a maximum Fsclk of 3.2MHz. Note that to simplify
--  downstream logic, the data is expanded to a 16-bit bus.
--
-- Revision History
-- Author          Date     Change
------------------ -------- ---------------------------------------------------
-- Seth Henry      05/18/23 Initial Upload
 
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;
 
entity adc12s022 is
generic(
  Clock_Frequency            : real;
  Reset_Level                : std_logic := '1'
);
port(
  Clock                      : in  std_logic;
  Reset                      : in  std_logic;
  --
  Reinit                     : in  std_logic := '0'; -- Optional sync reset
  --
  RAW_Channel                : out std_logic_vector(2 downto 0);
  RAW_Data                   : out std_logic_vector(15 downto 0);
  RAW_Valid                  : out std_logic;
  --
  Busy_In                    : in  std_logic;
  --
  SDO                        : in  std_logic;
  SDI                        : out std_logic;
  SCLK                       : out std_logic;
  CSn                        : out std_logic
);
end entity;
 
architecture behave of adc12s022 is
 
  -- The ceil_log2 function returns the minimum register width required to
  --  hold the supplied integer.
  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;
 
  -- Per the datasheet, the _022 part has a Fsmax of 3.2MHz, which results in
  --  a maximum single-channel conversion rate of 200ksps, or maximum
  --  multiplexed rate of 25ksps.
  constant ADS128S022_FSCLK  : real := 3200000.0;
 
  constant Clock_Ratio       : real :=
    ((Clock_Frequency + (0.5*ADS128S022_FSCLK)) / ADS128S022_FSCLK);
 
  constant Half_Period_Clks  : integer := integer(Clock_Ratio * 0.5);
 
  type ADC_STATES is ( INIT, IDLE, REQ_SP, SP_WAIT, INC_CH );
  signal ADC_State           : ADC_STATES := INIT;
 
  signal Channel             : std_logic_vector(2 downto 0) := "000";
  signal Conv_Start          : std_logic := '0';
 
  signal Data_Out            : std_logic_vector(11 downto 0) :=
                                 (others => '0');
  signal Valid               : std_logic := '0';
 
  constant Clk_Div_i         : integer := Half_Period_Clks - 1;
  constant Clk_Div_Bits      : integer := ceil_log2(Clk_Div_i);
  constant CLK_DIV_VAL       : std_logic_vector(Clk_Div_Bits - 1 downto 0) :=
                                conv_std_logic_vector(Clk_Div_i,Clk_Div_Bits);
  signal HT_Cntr             : std_logic_vector(Clk_Div_Bits - 1 downto 0);
  signal HT_Tick             : std_logic := '0';
 
  type SPI_STATES is ( IDLE, ALIGN, CSn_START, CLK_SETUP, CLK_HOLD, CSn_END );
  signal spi_state           : SPI_STATES;
 
  signal spi_wr_buffer       : std_logic_vector(15 downto 0) := x"0000";
  signal spi_rd_buffer       : std_logic_vector(15 downto 0) := x"0000";
 
  signal bit_cntr            : std_logic_vector(3 downto 0) := x"0";
 
begin
 
  ADC_Control_FSM_proc: process( Clock, Reset )
  begin
    if( Reset = Reset_Level )then
      ADC_State              <= INIT;
      Channel                <= (others => '0');
      Conv_Start             <= '0';
 
      RAW_Channel            <= (others => '0');
      RAW_Data               <= (others => '0');
      RAW_Valid              <= '0';
 
    elsif( rising_edge(Clock) )then
      Conv_Start             <= '0';
 
      RAW_Channel            <= (others => '0');
      RAW_Data               <= (others => '0');
      RAW_Valid              <= '0';
 
      case ADC_State is
        when INIT =>
          Channel            <= (others => '0');
          ADC_State          <= IDLE;
 
        when IDLE =>
          if( Reinit = '1' )then
            ADC_State        <= INIT;
          elsif( Busy_In = '0' )then
            ADC_State        <= REQ_SP;
          end if;
 
        when REQ_SP =>
          Conv_Start         <= '1';
          ADC_State          <= SP_WAIT;
 
        when SP_WAIT =>
          if( Valid = '1' )then
            RAW_Channel      <= Channel - 1;
            RAW_Data         <= "0000" & Data_Out;
            RAW_Valid        <= '1';
            ADC_State        <= INC_CH;
          end if;
 
        when INC_CH =>
          Channel            <= Channel + 1;
          ADC_State          <= IDLE;
 
        when others =>
          null;
      end case;
    end if;
  end process;
 
 
  SPI_IO_FSM: process( Clock, Reset )
  begin
    if( Reset = Reset_Level )then
      spi_state              <= IDLE;
      spi_wr_buffer          <= (others => '0');
      spi_rd_buffer          <= (others => '0');
      bit_cntr               <= (others => '0');
 
 
      HT_Cntr                <= (others => '0');
      HT_Tick                <= '0';
 
      SDI                    <= '0';
      SCLK                   <= '0';
      CSn                    <= '1';
 
      Data_Out               <= (others => '0');
      Valid                  <= '0';
    elsif( rising_edge(Clock) )then
 
      HT_Cntr                <= HT_Cntr - 1;
      HT_Tick                <= '0';
      if( HT_Cntr = 0 )then
        HT_Cntr              <= CLK_DIV_VAL;
        HT_Tick              <= '1';
      end if;
 
      SCLK                   <= '1';
      SDI                    <= '1';
 
      Valid                  <= '0';
 
      case( spi_state )is
        when IDLE =>
          CSn                <= '1';
          bit_cntr           <= x"F";
          if( Conv_Start = '1' )then
            spi_wr_buffer    <= "00" & Channel & "00000000000";
            spi_state        <= ALIGN;
          end if;
 
        when ALIGN =>
          if( HT_Tick = '1' )then
            spi_state        <= CSn_START;
          end if;
 
        when CSn_START =>
          CSn                <= '0';
          if( HT_Tick = '1' )then
            spi_state        <= CLK_SETUP;
          end if;
 
        when CLK_SETUP =>
          SCLK               <= '0';
          SDI                <= spi_wr_buffer(conv_integer(bit_cntr));
          CSn                <= '0';
          if( HT_Tick = '1' )then
            spi_rd_buffer    <= spi_rd_buffer(14 downto 0) & SDO;
            spi_state        <= CLK_HOLD;
          end if;
 
        when CLK_HOLD =>
          SDI                <= spi_wr_buffer(conv_integer(bit_cntr));
          if( HT_Tick = '1' )then
            bit_cntr         <= bit_cntr - 1;
            spi_state        <= CLK_SETUP;
            if( bit_cntr = 0 )then
              spi_state      <= CSn_END;
            end if;
          end if;
 
        when CSn_END =>
          if( HT_Tick = '1' )then
            Data_Out         <= spi_rd_buffer(11 downto 0);
            Valid            <= '1';
            spi_state        <= IDLE;
          end if;
 
        when others =>
          null;
      end case;
 
    end if;
  end process;
 
end architecture;