Subversion Repositories open8_urisc

-- VHDL Units :  o8_timer24

-- Description:  Provides an 24-bit microsecond resolution timer for generating

--            :   periodic interrupts for the Open8 CPU. This timer has a

--            :   programmable timebase selector that allows the resolution to

--            :   be set at run-time.

--

-- Register Map:

-- Offset  Bitfield Description                        Read/Write

--   0x00  AAAAAAAA Req Interval Byte 0                   (RW)

--   0x01  AAAAAAAA Req Interval Byte 1                   (RW)

--   0x02  AAAAAAAA Req Interval Byte 2                   (RW)

--   0x03  CBA----- Control/Status Register               (RW)

--                   A: Update timer (WR) or pending (RD)

--                   B: Timebase (0 = uS / 1 = mS)

--                   C: Output Enable

--

-- Notes      :  Setting the output to 0x000000 OR clearing bit C will disable

--            :   the timer.

--            :  Update pending is true if bit A is 1, otherwise false

--

-- Revision History

-- Author          Date     Change

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

-- Seth Henry      05/17/23 Initial upload (based on sys_timer_ii)

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_timer24 is

generic(

  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

);

end entity;

architecture behave of o8_timer24 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 := '0';

  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;

  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 Req_Interval        : std_logic_vector(23 downto 0) := x"000000";

  alias  Req_Interval_B0     is Req_Interval( 7 downto  0);

  alias  Req_Interval_B1     is Req_Interval(15 downto  8);

  alias  Req_Interval_B2     is Req_Interval(23 downto 16);

  signal Int_Interval        : std_logic_vector(23 downto 0) := x"000000";

  signal Timebase            : std_logic := '0';

  signal Update_Interval     : std_logic := '0';

  signal Update_Pending      : std_logic := '0';

  signal Output_Enable       : std_logic := '0';

  signal Output_Qual         : std_logic := '0';

  signal Timer_Cnt           : std_logic_vector(23 downto 0) := x"000000";

  constant MSEC_DELAY        : std_logic_vector(9 downto 0) :=

                                conv_std_logic_vector(1000,10);

  signal mSec_Timer          : std_logic_vector(9 downto 0) := (others => '0');

  signal mSec_Tick           : std_logic := '0';

  signal Timer_Tick          : std_logic := '0';

begin

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

  Wr_En_d                    <= Addr_Match and Open8_Bus.Wr_En;

  Rd_En_d                    <= Addr_Match and Open8_Bus.Rd_En;

  mSec_Tick_proc: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

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

      mSec_Tick             <= '0';

    elsif( rising_edge(Clock) )then

      mSec_Timer            <= mSec_Timer - uSec_Tick;

      mSec_Tick             <= '0';

      if( mSec_Timer = 0 )then

        mSec_Timer          <= MSEC_DELAY;

        mSec_Tick           <= '1';

      end if;

    end if;

  end process;

  Timer_Tick                 <= mSec_Tick when Timebase = '1' else uSec_Tick;

  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;

      Req_Interval           <= x"000000";

      Update_Interval        <= '0';

      Update_Pending         <= '0';

      Timebase               <= '0';

      Output_Enable          <= '0';

    elsif( rising_edge( Clock ) )then

      Reg_Sel_q              <= Reg_Sel_d;

      Wr_En_q                <= Wr_En_d;

      Wr_Data_q              <= Wr_Data_d;

      Update_Interval        <= '0';

      if( Wr_En_q = '1' and Write_Qual = '1' )then

        case( Reg_Sel_q )is

          when "00" =>

            Req_Interval_B0  <= Wr_Data_q;

            Update_Pending   <= '1';

          when "01" =>

            Req_Interval_B1  <= Wr_Data_q;

            Update_Pending   <= '1';

          when "10" =>

            Req_Interval_B2  <= Wr_Data_q;

            Update_Pending   <= '1';

          when "11" =>

            Output_Enable    <= Wr_Data_q(7);

            Timebase         <= Wr_Data_q(6);

            Update_Interval  <= Wr_Data_q(5);

          when others => null;

        end case;

      end if;

      if( Update_Interval = '1' )then

        Update_Pending       <= '0';

      end if;

      Rd_Data                <= OPEN8_NULLBUS;

      Rd_En_q                <= Rd_En_d;

      if( Rd_En_q = '1' )then

        case( Reg_Sel_q )is

          when "00" =>

            Rd_Data          <= Req_Interval_B0;

          when "01" =>

            Rd_Data          <= Req_Interval_B1;

          when "10" =>

            Rd_Data          <= Req_Interval_B2;

          when "11" =>

            Rd_Data          <= Output_Enable & Timebase &

                                Update_Pending & "00000";

          when others => null;

        end case;

      end if;

    end if;

  end process;

  Interval_proc: process( Clock, Reset )

  begin

    if( Reset = Reset_Level )then

      Output_Qual            <= '0';

      Int_Interval           <= x"000000";

      Timer_Cnt              <= x"000000";

      Interrupt              <= '0';

    elsif( rising_edge(Clock) )then

      Output_Qual            <= Output_Enable and or_reduce(Int_Interval);

      Interrupt              <= '0';

      Timer_Cnt              <= Timer_Cnt - Timer_Tick;

      if( Update_Interval = '1' )then

        Int_Interval         <= Req_Interval;

        Timer_Cnt            <= Req_Interval;

      elsif( or_reduce(Timer_Cnt) = '0' )then

        Timer_Cnt            <= Int_Interval;

        Interrupt            <= Output_Qual;

      end if;

    end if;

  end process;

end architecture;