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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
-- 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: o8_hd44780_if
-- Description: Provides low-level access to "standard" character LCDs using
--               the ST/HD44780(U) control ASIC wired in either 8-bit or
--               reduced (4-bit) mode.
--              All low-level timing of the control signals are handled by this
--               module, allowing client firmware to use a simple register
--               interface to program the LCD panel.
-- Note that this module assumes that the R/Wn line has been tied LOW
--
-- Register Map
-- Address  Function
-- Offset  Bitfield Description                        Read/Write
-- 0x0     AAAAAAAA LCD Register Write                 (Read-Write*)
-- 0x1     AAAAAAAA LCD Data Write                     (Read-Write*)
-- 0x2     AAAAAAAA LCD Rearm Init Timer               (Read-Write*)
-- 0x3     AAAAAAAA LCD Backlight                      (Read-Write)
--
-- Note: Reading 0x0, 0x1 or 0x2 will report whether the panel is ready or not
--        in the MSB (bit 7). 0x00 = NOT READY / 0x80 = READY
--
--------------------------------------------------------------------------------
-- LCD Controller
--------------------------------------------------------------------------------
--
-- LCD Instruction Set (Hitachi Compatible)
-- Instruction             RS  RW  D7  D6  D5  D4  D3  D2  D1  D0  Time
------------------------------------------------------------------------
-- Clear Display         | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1.52mS
-- Return Home           | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | x | 1.52mS
-- Entry Mode            | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | ID| S |   37uS
-- Display Pwr           | 0 | 0 | 0 | 0 | 0 | 0 | 1 | D | C | B |   37uS
-- Cursor/Display Shift  | 0 | 0 | 0 | 0 | 0 | 1 | SC| RL| x | x |   37uS
-- Function Set          | 0 | 0 | 0 | 0 | 1 | DL| N | F | x | x |   37uS
-- Set CGRAM Address     | 0 | 0 | 0 | 1 | A | A | A | A | A | A |   37uS
-- Set DDRAM Address     | 0 | 0 | 1 | A | A | A | A | A | A | A |   37uS
 
-- LCD Instruction Set (New Haven)
-- Instruction             RS  RW  D7  D6  D5  D4  D3  D2  D1  D0  Time
------------------------------------------------------------------------
-- Clear Display         | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 2.00mS
-- Return Home           | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | x |  600uS
-- Entry Mode            | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | ID| S |  600uS
-- Display Pwr           | 0 | 0 | 0 | 0 | 0 | 0 | 1 | D | C | B |  600uS
-- Cursor/Display Shift  | 0 | 0 | 0 | 0 | 0 | 1 | SC| RL| x | x |  600uS
-- Function Set          | 0 | 0 | 0 | 0 | 1 | DL| N | F | T | T |  600uS
-- Set CGRAM Address     | 0 | 0 | 0 | 1 | A | A | A | A | A | A |  600uS
-- Set DDRAM Address     | 0 | 0 | 1 | A | A | A | A | A | A | A |  600uS
--
-- Notes:
-- ID = Increment/Decrement DDRAM Address (1 = increment, 0 = decrement)
-- S  = Shift Enable (1 = Shift display according to ID, 0 = Don't shift)
-- D  = Display On/Off (1 = on, 0 = off)
-- C  = Cursor On/Off  (1 = on, 0 = off)
-- B  = Cursor Blink   (1 = block cursor, 0 = underline cursor)
-- SC / RL = Shift Cursor/Display Right/Left (see data sheet - not needed for init)
-- F  = Font (0 = 5x8, 1 = 5x11) Ignored on 2-line displays (N = 1)
-- N  = Number of Lines (0 = 1 lines, 1 = 2 lines)
-- DL = Data Length (0 = 4-bit bus, 1 = 8-bit bus) This is fixed at 1 in this module
-- A  = Address (see data sheet for usage)
-- T  = New Haven Only - Changes the character set (see data sheet)
--
-- Revision History
-- Author          Date     Change
------------------ -------- ---------------------------------------------------
-- Seth Henry      04/12/21 Design Start
 
 
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_hd44780_if is
generic(
  Use_4Bit_IF                : boolean := FALSE;
  -- LCD bus IF timing
  Tas                        : integer :=    20; -- ns
  Tpwe                       : integer :=   450; -- nS
  Tcyce                      : integer :=  1000; -- nS
  -- LCD command timing
  Tpwrdly                    : integer := 40000; -- uS
  Tcldsp                     : integer :=  2000; -- uS
  Tbusy                      : integer :=    50; -- uS
  -- Backlight
  Use_Backlight              : boolean := FALSE;
  Default_Brightness         : std_logic_vector(7 downto 0) := x"00";
  -- System clock & address
  Clock_Frequency            : real;
  Address                    : ADDRESS_TYPE
);
port(
  Open8_Bus                  : in  OPEN8_BUS_TYPE;
  Write_Qual                 : in  std_logic := '1';
  Rd_Data                    : out DATA_TYPE;
  Interrupt                  : out std_logic;
  --
  LCD_E                      : out std_logic;
  LCD_RS                     : out std_logic;
  LCD_DQ                     : out std_logic_vector(7 downto 0);
  LCD_BL                     : out std_logic
);
end entity;
 
architecture behave of o8_hd44780_if 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 2)
                               := Address(15 downto 2);
  alias  Comp_Addr           is Open8_Bus.Address(15 downto 2);
  signal Addr_Match          : std_logic;
 
  alias  Reg_Sel_d           is Open8_Bus.Address(1 downto 0);
  signal Reg_Sel_q           : std_logic_vector(1 downto 0) := "00";
  signal Wr_En_d             : std_logic := '0';
  signal Wr_En_q             : std_logic := '0';
  alias  Wr_Data_d           is Open8_Bus.Wr_Data;
  signal Wr_Data_q           : DATA_TYPE := x"00";
  signal Rd_En_d             : std_logic := '0';
  signal Rd_En_q             : std_logic := '0';
 
  signal Rearm_Init          : std_logic := '0';
 
  signal Reg_Valid           : std_logic := '0';
  signal Reg_Sel             : std_logic := '0';
  signal Reg_Data            : std_logic_vector(7 downto 0) := x"00";
 
  signal Tx_Ready            : std_logic := '0';
 
  constant HW_TMR_BITS       : integer := ceil_log2(Tpwrdly);
  constant TPWR_DELAY        : std_logic_vector(HW_TMR_BITS-1 downto 0) :=
                               conv_std_logic_vector(Tpwrdly,HW_TMR_BITS);
 
  constant CLDSP_DELAY       : std_logic_vector(HW_TMR_BITS-1 downto 0) :=
                               conv_std_logic_vector(Tcldsp,HW_TMR_BITS);
 
  constant BUSY_DELAY        : std_logic_vector(HW_TMR_BITS-1 downto 0) :=
                               conv_std_logic_vector(Tbusy, HW_TMR_BITS);
 
  signal hw_timer            : std_logic_vector(HW_TMR_BITS-1 downto 0);
 
  type CTRL_STATES is (INIT, PWR_WAIT, IDLE, PREP_WR, ISSUE_WR, WR_WAIT,
                       BUSY_WAIT, ISSUE_INT );
 
  signal ctrl_state          : CTRL_STATES := INIT;
 
  signal Wr_Fnset            : std_logic := '0';
  signal Wr_Data             : DATA_TYPE := x"00";
  signal Wr_Reg              : std_logic := '0';
  signal Wr_En               : std_logic := '0';
 
  signal IO_Done             : std_logic := '0';
 
  signal LCD_Data            : DATA_TYPE := x"00";
  signal LCD_Addr            : std_logic := '0';
 
--------------------------------------------------------------------------------
-- Backlight signals
--------------------------------------------------------------------------------
 
  signal LCD_Bright          : DATA_TYPE := x"00";
 
begin
 
--------------------------------------------------------------------------------
-- Open8 Register interface
--------------------------------------------------------------------------------
 
  Addr_Match                 <= '1' when Comp_Addr = User_Addr else '0';
  Wr_En_d                    <= Addr_Match and Open8_Bus.Wr_En and Write_Qual;
  Rd_En_d                    <= Addr_Match and Open8_Bus.Rd_En;
 
  io_reg: process( Clock, Reset )
  begin
    if( Reset = Reset_Level )then
      Reg_Sel_q              <= "00";
      Wr_En_q                <= '0';
      Wr_Data_q              <= x"00";
      Rd_En_q                <= '0';
      Rd_Data                <= OPEN8_NULLBUS;
 
      Rearm_Init             <= '0';
 
      Reg_Valid              <= '0';
      Reg_Sel                <= '0';
      Reg_Data               <= x"00";
 
      LCD_Bright             <= Default_Brightness;
    elsif( rising_edge( Clock ) )then
      Reg_Sel_q              <= Reg_Sel_d;
 
      Rearm_Init             <= '0';
 
      Wr_En_q                <= Wr_En_d;
      Wr_Data_q              <= Wr_Data_d;
      Reg_Valid              <= '0';
      if( Wr_En_q = '1' )then
        case( Reg_Sel_q )is
          when "00" | "01" =>
            Reg_Valid        <= '1';
            Reg_Sel          <= Reg_Sel_q(0);
            Reg_Data         <= Wr_Data_q;
          when "10" =>
            Rearm_Init       <= '1';
          when "11" =>
            LCD_Bright       <= Wr_Data_q;
          when others => null;
        end case;
      end if;
 
      Rd_En_q                <= Rd_En_d;
      Rd_Data                <= OPEN8_NULLBUS;
      if( Rd_En_q = '1' )then
        case( Reg_Sel_q )is
          when "00" | "01" | "10" =>
            Rd_Data(7)       <= Tx_Ready;
          when "11" =>
            Rd_Data          <= LCD_Bright;
          when others => null;
        end case;
      end if;
    end if;
  end process;
 
--------------------------------------------------------------------------------
-- LCD and Register logic
--------------------------------------------------------------------------------
 
  LCD_Ctrl_proc: process( Clock, Reset )
  begin
    if( Reset = Reset_Level )then
      ctrl_state             <= INIT;
      hw_timer               <= (others => '0');
      Wr_Fnset               <= '0';
      Wr_Data                <= x"00";
      Wr_Reg                 <= '0';
      Wr_En                  <= '0';
      Tx_Ready               <= '0';
      Interrupt              <= '0';
    elsif( rising_edge(Clock) )then
      Wr_En                  <= '0';
      Tx_Ready               <= '0';
      Interrupt              <= '0';
      hw_timer               <= hw_timer - uSec_Tick;
      case( ctrl_state )is
 
        when INIT =>
          hw_timer           <= TPWR_DELAY;
          ctrl_state         <= PWR_WAIT;
 
        when PWR_WAIT =>
          if( hw_timer = 0 )then
            ctrl_state       <= IDLE;
          end if;
 
        when IDLE =>
          Tx_Ready           <= '1';
          if( Rearm_Init = '1' )then
            ctrl_state       <= INIT;
          elsif( Reg_Valid = '1' )then
            Wr_Reg           <= Reg_Sel;
            Wr_Data          <= Reg_Data;
            ctrl_state       <= PREP_WR;
          end if;
 
        when PREP_WR =>
          Wr_Fnset           <= '0';
          -- Trap on Function Set if we are in 4-bit mode, so that we can issue
          --  the first nibble twice.
          if( Use_4Bit_IF and
              Wr_Reg = '0' and
              Wr_Data(7 downto 4) = "0010" )then
            Wr_Fnset         <= '1';
          end if;
            ctrl_state       <= ISSUE_WR;
 
        when ISSUE_WR =>
          Wr_En              <= '1';
          hw_timer           <= BUSY_DELAY;
          if( Wr_Reg = '0' and Wr_Data < 4 )then
            hw_timer         <= CLDSP_DELAY;
          end if;
          ctrl_state         <= WR_WAIT;
 
        when WR_WAIT =>
          if( IO_Done = '1' )then
            ctrl_state       <= BUSY_WAIT;
          end if;
 
        when BUSY_WAIT =>
          if( hw_timer = 0 )then
            ctrl_state       <= ISSUE_INT;
          end if;
 
        when ISSUE_INT =>
          Interrupt          <= '1';
          ctrl_state         <= IDLE;
 
        when others => null;
 
      end case;
 
    end if;
  end process;
 
--------------------------------------------------------------------------------
-- Low-level I/O drivers
--------------------------------------------------------------------------------
 
IF_Type_4bit: if( Use_4Bit_IF )generate
 
  U_IO : entity work.hd44780_4b
  generic map(
    Tas                      => Tas,
    Tpwe                     => Tpwe,
    Tcyce                    => Tcyce,
    Clock_Frequency          => Clock_Frequency,
    Reset_Level              => Reset_Level
  )
  port map(
    Clock                    => Clock,
    Reset                    => Reset,
    --
    Wr_Fnset                 => Wr_Fnset,
    Wr_Data                  => Wr_Data,
    Wr_Reg                   => Wr_Reg,
    Wr_En                    => Wr_En,
    --
    IO_Done                  => IO_Done,
    --
    LCD_RS                   => LCD_RS,
    LCD_E                    => LCD_E,
    LCD_DQ                   => LCD_DQ
  );
 
end generate;
 
IF_Type_8bit: if( not Use_4Bit_IF )generate
 
  U_IO : entity work.hd44780_8b
  generic map(
    Tas                      => Tas,
    Tpwe                     => Tpwe,
    Tcyce                    => Tcyce,
    Clock_Frequency          => Clock_Frequency,
    Reset_Level              => Reset_Level
  )
  port map(
    Clock                    => Clock,
    Reset                    => Reset,
    --
    Wr_Data                  => Wr_Data,
    Wr_Reg                   => Wr_Reg,
    Wr_En                    => Wr_En,
    --
    IO_Done                  => IO_Done,
    --
    LCD_RS                   => LCD_RS,
    LCD_E                    => LCD_E,
    LCD_DQ                   => LCD_DQ
  );
 
end generate;
 
--------------------------------------------------------------------------------
-- Backlight control logic (optional)
--------------------------------------------------------------------------------
 
Backlight_Disabled: if( not Use_Backlight )generate
  LCD_BL                <= '0';
end generate;
 
Backlight_Enabled: if( Use_Backlight )generate
 
  U_BL : entity work.vdsm8
  generic map(
    Reset_Level              => Reset_Level
  )
  port map(
    Clock                    => Clock,
    Reset                    => Reset,
    DACin                    => LCD_Bright,
    DACout                   => LCD_BL
  );
 
end generate;
 
end architecture;