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-- 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 Units :  o8_max7221

-- Description:  Provides a memory mapped SPI interface to the max7221 LED

--                controller/driver.

--

-- Revision History

-- Author          Date     Change

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

-- Seth Henry      01/22/20 Design Start

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_max7221 is

generic(

  Bit_Rate              : real := 5000000.0;

  Sys_Freq              : real;

  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;

  --

  Mx_Data               : out std_logic;

  Mx_Clock              : out std_logic;

  MX_LDCSn              : out std_logic

);

end entity;

architecture behave of o8_max7221 is

  signal FIFO_Reset     : std_logic;

  constant User_Addr    : std_logic_vector(15 downto 4) := Address(15 downto 4);

  alias  Comp_Addr      is Bus_Address(15 downto 4);

  signal FIFO_Wr_En     : std_logic;

  signal FIFO_Wr_Data   : std_logic_vector(11 downto 0);

  signal FIFO_Rd_En     : std_logic;

  signal FIFO_Empty     : std_logic;

  signal FIFO_Rd_Data   : std_logic_vector(11 downto 0);

  type TX_CTRL_STATES is (IDLE, TX_BYTE, TX_START, TX_WAIT );

  signal TX_Ctrl        : TX_CTRL_STATES;

  signal TX_En          : std_logic;

  signal TX_Idle        : std_logic;

  constant BAUD_DLY_VAL : integer := integer((Sys_Freq / Bit_Rate) / 2.0 );

  constant BAUD_DLY_WDT : integer := ceil_log2(BAUD_DLY_VAL - 1);

  constant BAUD_DLY     : std_logic_vector :=

                           conv_std_logic_vector(BAUD_DLY_VAL - 1, BAUD_DLY_WDT);

  signal Baud_Cntr      : std_logic_vector( BAUD_DLY_WDT - 1 downto 0 )

                          := (others => '0');

  signal Baud_Tick      : std_logic;

  type IO_STATES is ( IDLE, SYNC_CLK, SCLK_L, SCLK_H, ADV_BIT, DONE );

  signal io_state       : IO_STATES;

  signal bit_cntr       : std_logic_vector(3 downto 0);

  signal tx_buffer      : std_logic_vector(15 downto 0);

begin

  FIFO_Wr_En            <= Wr_Enable when Comp_Addr = User_Addr else '0';

  FIFO_Wr_Data          <= Bus_Address(3 downto 0) & Wr_Data;

  FIFO_Reset            <= Reset when Reset_Level = '1' else (not Reset);

  U_FIFO : entity work.o8_max7221_fifo

  port map(

    aclr                => FIFO_Reset,

    clock               => Clock,

    data                => FIFO_Wr_Data,

    rdreq               => FIFO_Rd_En,

    wrreq               => FIFO_Wr_En,

    empty               => FIFO_Empty,

    q                   => FIFO_Rd_Data

  );

  tx_FSM: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      TX_Ctrl          <= IDLE;

      TX_En            <= '0';

      FIFO_Rd_En       <= '0';

    elsif( rising_edge(Clock) )then

      TX_En            <= '0';

      FIFO_Rd_En       <= '0';

      case( TX_Ctrl )is

        when IDLE =>

          if( FIFO_Empty = '0' )then

            FIFO_Rd_En  <= '1';

            TX_Ctrl     <= TX_BYTE;

          end if;

        when TX_BYTE =>

          TX_En         <= '1';

          TX_Ctrl       <= TX_START;

        when TX_START =>

          if( TX_Idle = '0' )then

            TX_Ctrl     <= TX_WAIT;

          end if;

        when TX_WAIT =>

          if( TX_Idle = '1' )then

            TX_Ctrl     <= IDLE;

          end if;

        when others => null;

      end case;

    end if;

  end process;

  Baud_Rate_proc: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

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

      Baud_Tick         <= '0';

    elsif( rising_edge( Clock ) )then

      Baud_Cntr         <= Baud_Cntr - 1;

      Baud_Tick         <= nor_reduce(Baud_Cntr);

      if( Baud_Cntr = 0 )then

        Baud_Cntr       <= BAUD_DLY;

      end if;

    end if;

  end process;

  io_FSM: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      io_state          <= IDLE;

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

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

      TX_Idle           <= '0';

      Mx_Clock          <= '0';

      Mx_Data           <= '0';

      MX_LDCSn          <= '0';

    elsif( rising_edge(Clock) )then

      TX_Idle           <= '0';

      Mx_Clock          <= '0';

      case( io_state )is

        when IDLE =>

          Mx_Data       <= '0';

          MX_LDCSn      <= '1';

          TX_Idle       <= '1';

          if( TX_En = '1' )then

            tx_buffer   <= "0000" & FIFO_Rd_Data;

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

            io_state    <= SYNC_CLK;

          end if;

        when SYNC_CLK =>

          if( Baud_Tick = '1' )then

            io_state    <= SCLK_L;

          end if;

        when SCLK_L =>

          MX_LDCSn      <= '0';

          Mx_Data       <= tx_buffer(conv_integer(bit_cntr));

          if( Baud_Tick = '1' )then

            io_state    <= SCLK_H;

          end if;

        when SCLK_H =>

          Mx_Clock      <= '1';

          if( Baud_Tick = '1' )then

            bit_cntr    <= bit_cntr - 1;

            io_state    <= ADV_BIT;

          end if;

        when ADV_BIT =>

          io_state      <= SCLK_L;

          if( and_reduce(bit_cntr) = '1' )then

            io_state    <= DONE;

          end if;

        when DONE =>

          Mx_Data       <= '0';

          if( Baud_Tick = '1' )then

            io_state    <= IDLE;

          end if;

        when others => null;

      end case;

    end if;

  end process;

end architecture;