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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

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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 :  o8_rtc

-- Description:  Provides automatically updated registers that maintain the

--            :   time of day. Keeps track of the day of week, hours, minutes

--            :   seconds, and tenths of a second. Module is doubled buffered

--            :   to ensure time consistency during accesses. Also provides

--            :   a programmable periodic interrupt timer, as well as a uSec

--            :    tick for external use.

--

-- Register Map:

-- Offset  Bitfield Description                        Read/Write

--   0x0   AAAAAAAA Periodic Interval Timer in uS      (RW)

--   0x1   -AAAAAAA Tenths  (0x00 - 0x63)              (RW)

--   0x2   --AAAAAA Seconds (0x00 - 0x3B)              (RW)

--   0x3   --AAAAAA Minutes (0x00 - 0x3B)              (RW)

--   0x4   ---AAAAA Hours   (0x00 - 0x17)              (RW)

--   0x5   -----AAA Day of Week (0x00 - 0x06)          (RW)

--   0x6   -------- Update RTC regs from Shadow Regs   (WO)

--   0x7   A------- Update Shadow Regs from RTC regs   (RW)

--                  A = Update is Busy

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_rtc is

generic(

  Sys_Freq                   : real;

  Reset_Level                : std_logic;

  Address                    : ADDRESS_TYPE

);

port(

  Clock                      : in  std_logic;

  Reset                      : in  std_logic;

  uSec_Tick                  : out std_logic;

  --

  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_PIT              : out std_logic;

  Interrupt_RTC              : out std_logic

);

end entity;

architecture behave of o8_rtc is

  constant User_Addr         : std_logic_vector(15 downto 3)

                               := Address(15 downto 3);

  alias  Comp_Addr           is Bus_Address(15 downto 3);

  signal Addr_Match          : std_logic;

  alias  Reg_Addr            is Bus_Address(2 downto 0);

  signal Reg_Addr_q          : std_logic_vector(2 downto 0);

  signal Wr_En               : std_logic;

  signal Wr_Data_q           : DATA_TYPE;

  signal Rd_En               : std_logic;

  constant DLY_1USEC_VAL     : integer := integer(Sys_Freq / 1000000.0);

  constant DLY_1USEC_WDT     : integer := ceil_log2(DLY_1USEC_VAL - 1);

  constant DLY_1USEC         : std_logic_vector :=

                     conv_std_logic_vector( DLY_1USEC_VAL - 1, DLY_1USEC_WDT);

  signal uSec_Cntr           : std_logic_vector( DLY_1USEC_WDT - 1 downto 0 )

                               := (others => '0');

  signal uSec_Tick_i         : std_logic;

  type PIT_TYPE is record

    timer_cnt           : DATA_TYPE;

    timer_ro            : std_logic;

  end record;

  signal pit            : PIT_TYPE;

  type RTC_TYPE is record

    frac                : std_logic_vector(15 downto 0);

    frac_ro             : std_logic;

    tens_l              : std_logic_vector(3 downto 0);

    tens_l_ro           : std_logic;

    tens_u              : std_logic_vector(3 downto 0);

    tens_u_ro           : std_logic;

    secs_l              : std_logic_vector(3 downto 0);

    secs_l_ro           : std_logic;

    secs_u              : std_logic_vector(3 downto 0);

    secs_u_ro           : std_logic;

    mins_l              : std_logic_vector(3 downto 0);

    mins_l_ro           : std_logic;

    mins_u              : std_logic_vector(3 downto 0);

    mins_u_ro           : std_logic;

    hours_l             : std_logic_vector(3 downto 0);

    hours_l_ro          : std_logic;

    hours_u             : std_logic_vector(3 downto 0);

    hours_u_ro          : std_logic;

    dow                 : std_logic_vector(2 downto 0);

  end record;

  constant DECISEC      : std_logic_vector(15 downto 0) :=

                           conv_std_logic_vector(10000,16);

  signal rtc            : RTC_TYPE;

  signal interval       : DATA_TYPE;

  signal update_interval: std_logic;

  signal new_interval   : DATA_TYPE;

  signal shd_tens       : DATA_TYPE;

  signal shd_secs       : DATA_TYPE;

  signal shd_mins       : DATA_TYPE;

  signal shd_hours      : DATA_TYPE;

  signal shd_dow        : DATA_TYPE;

  signal update_rtc     : std_logic;

  signal update_shd     : std_logic;

  signal update_ctmr    : std_logic_vector(3 downto 0);

begin

  uSec_Tick                  <= uSec_Tick_i;

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

  Interrupt_PIT              <= pit.timer_ro;

  Interrupt_RTC              <= rtc.frac_ro;

  io_reg: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

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

      uSec_Tick_i            <= '0';

      pit.timer_cnt          <= x"00";

      pit.timer_ro           <= '0';

      rtc.frac               <= DECISEC;

      rtc.frac_ro            <= '0';

      rtc.tens_l             <= (others => '0');

      rtc.tens_l_ro          <= '0';

      rtc.tens_u             <= (others => '0');

      rtc.tens_u_ro          <= '0';

      rtc.secs_l             <= (others => '0');

      rtc.secs_l_ro          <= '0';

      rtc.secs_u             <= (others => '0');

      rtc.secs_u_ro          <= '0';

      rtc.mins_l             <= (others => '0');

      rtc.mins_l_ro          <= '0';

      rtc.mins_u             <= (others => '0');

      rtc.mins_u_ro          <= '0';

      rtc.hours_l            <= (others => '0');

      rtc.hours_l_ro         <= '0';

      rtc.hours_u            <= (others => '0');

      rtc.hours_u_ro         <= '0';

      rtc.dow                <= (others => '0');

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

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

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

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

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

      update_rtc             <= '0';

      update_shd             <= '0';

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

      interval               <= x"00";

      update_interval        <= '0';

      new_interval           <= x"00";

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

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

      Wr_En                  <= '0';

      Rd_En                  <= '0';

      Rd_Data                <= OPEN8_NULLBUS;

    elsif( rising_edge( Clock ) )then

      uSec_Cntr              <= uSec_Cntr - 1;

      uSec_Tick_i            <= '0';

      if( uSec_Cntr = 0 )then

        uSec_Cntr            <= DLY_1USEC;

        uSec_Tick_i          <= '1';

      end if;

      -- Periodic Interval Timer

      pit.timer_cnt          <= pit.timer_cnt - uSec_Tick_i;

      pit.timer_ro           <= '0';

      if( update_interval = '1' )then

        pit.timer_cnt        <= new_interval;

      elsif( or_reduce(pit.timer_cnt) = '0' )then

        pit.timer_cnt        <= interval;

        pit.timer_ro         <= or_reduce(interval);

      end if;

      -- Fractional decisecond counter - cycles every 10k microseconds

      rtc.frac               <= rtc.frac - uSec_Tick_i;

      rtc.frac_ro            <= '0';

      if( or_reduce(rtc.frac) = '0' or update_rtc = '1' )then

        rtc.frac             <= DECISEC;

        rtc.frac_ro          <= not update_rtc;

      end if;

      -- Decisecond counter (lower)

      rtc.tens_l             <= rtc.tens_l + rtc.frac_ro;

      rtc.tens_l_ro          <= '0';

      if( update_rtc = '1' )then

        rtc.tens_l           <= shd_tens(3 downto 0);

      elsif( rtc.tens_l > x"9")then

        rtc.tens_l           <= (others => '0');

        rtc.tens_l_ro        <= '1';

      end if;

      -- Decisecond counter (upper)

      rtc.tens_u             <= rtc.tens_u + rtc.tens_l_ro;

      rtc.tens_u_ro          <= '0';

      if( update_rtc = '1' )then

        rtc.tens_u           <= shd_tens(7 downto 4);

      elsif( rtc.tens_u > x"9")then

        rtc.tens_u           <= (others => '0');

        rtc.tens_u_ro        <= '1';

      end if;

      -- Second counter (lower)

      rtc.secs_l             <= rtc.secs_l + rtc.tens_u_ro;

      rtc.secs_l_ro          <= '0';

      if( update_rtc = '1' )then

        rtc.secs_l           <= shd_secs(3 downto 0);

      elsif( rtc.secs_l > x"9")then

        rtc.secs_l           <= (others => '0');

        rtc.secs_l_ro        <= '1';

      end if;

      -- Second counter (upper)

      rtc.secs_u             <= rtc.secs_u + rtc.secs_l_ro;

      rtc.secs_u_ro          <= '0';

      if( update_rtc = '1' )then

        rtc.secs_u           <= shd_secs(7 downto 4);

      elsif( rtc.secs_u > x"5")then

        rtc.secs_u           <= (others => '0');

        rtc.secs_u_ro        <= '1';

      end if;

      -- Minutes counter (lower)

      rtc.mins_l             <= rtc.mins_l + rtc.secs_u_ro;

      rtc.mins_l_ro          <= '0';

      if( update_rtc = '1' )then

        rtc.mins_l           <= shd_mins(3 downto 0);

      elsif( rtc.mins_l > x"9")then

        rtc.mins_l           <= (others => '0');

        rtc.mins_l_ro        <= '1';

      end if;

      -- Minutes counter (upper)

      rtc.mins_u             <= rtc.mins_u + rtc.mins_l_ro;

      rtc.mins_u_ro          <= '0';

      if( update_rtc = '1' )then

        rtc.mins_u           <= shd_mins(7 downto 4);

      elsif( rtc.mins_u > x"5")then

        rtc.mins_u           <= (others => '0');

        rtc.mins_u_ro        <= '1';

      end if;

      -- Hour counter (lower)

      rtc.hours_l            <= rtc.hours_l + rtc.mins_u_ro;

      rtc.hours_l_ro         <= '0';

      if( update_rtc = '1' )then

        rtc.hours_l          <= shd_hours(3 downto 0);

      elsif( rtc.hours_l > x"9")then

        rtc.hours_l          <= (others => '0');

        rtc.hours_l_ro       <= '1';

      end if;

      -- Hour counter (upper)

      rtc.hours_u            <= rtc.hours_u + rtc.hours_l_ro;

      if( update_rtc = '1' )then

        rtc.hours_u          <= shd_hours(7 downto 4);

      end if;

      rtc.hours_u_ro         <= '0';

      if( rtc.hours_u >= x"2" and rtc.hours_l > x"3" )then

        rtc.hours_l          <= (others => '0');

        rtc.hours_u          <= (others => '0');

        rtc.hours_u_ro       <= '1';

      end if;

      -- Day of Week counter

      rtc.dow                <= rtc.dow + rtc.hours_u_ro;

      if( update_rtc = '1' )then

        rtc.dow              <= shd_dow(2 downto 0);

      elsif( rtc.dow = x"07")then

        rtc.dow              <= (others => '0');

      end if;

      -- Copy the RTC registers to the shadow registers when the coherency

      --  timer is zero (RTC registers are static)

      if( update_shd = '1' and or_reduce(update_ctmr) = '0' )then

        shd_tens             <= rtc.tens_u & rtc.tens_l;

        shd_secs             <= rtc.secs_u & rtc.secs_l;

        shd_mins             <= rtc.mins_u & rtc.mins_l;

        shd_hours            <= rtc.hours_u & rtc.hours_l;

        shd_dow              <= "00000" & rtc.dow;

        update_shd           <= '0';

      end if;

      update_interval        <= '0';

      Reg_Addr_q             <= Reg_Addr;

      Wr_Data_q              <= Wr_Data;

      Wr_En                  <= Addr_Match and Wr_Enable;

      update_rtc             <= '0';

      if( Wr_En = '1' )then

        case( Reg_Addr_q )is

          when "000" =>

            new_interval     <= Wr_Data_q;

            update_interval  <= '1';

          when "001" =>

            shd_tens         <= Wr_Data_q;

          when "010" =>

            shd_secs         <= Wr_Data_q;

          when "011" =>

            shd_mins         <= Wr_Data_q;

          when "100" =>

            shd_hours        <= Wr_Data_q;

          when "101" =>

            shd_dow          <= Wr_Data_q;

          when "110" =>

            update_rtc       <= '1';

          when "111" =>

            update_shd  <= '1';

          when others => null;

        end case;

      end if;

      -- Coherency timer - ensures that the shadow registers are updated with

      --  valid time data by delaying updates until the rtc registers have

      --  finished cascading.

      update_ctmr            <= update_ctmr - or_reduce(update_ctmr);

      if( rtc.frac_ro = '1' )then

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

      end if;

      Rd_Data                <= OPEN8_NULLBUS;

      Rd_En                  <= Addr_Match and Rd_Enable;

      if( Rd_En = '1' )then

        case( Reg_Addr_q )is

          when "000" =>

            Rd_Data          <= interval;

          when "001" =>

            Rd_Data          <= shd_tens;

          when "010" =>

            Rd_Data          <= shd_secs;

          when "011" =>

            Rd_Data          <= shd_mins;

          when "100" =>

            Rd_Data          <= shd_hours;

          when "101" =>

            Rd_Data          <= shd_dow;

          when "110" =>

            null;

          when "111" =>

            Rd_Data          <= update_shd & "0000000";

          when others => null;

        end case;

      end if;

    end if;

  end process;

end architecture;