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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;