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[/] [open8_urisc/] [trunk/] [VHDL/] [o8_sys_timer.vhd] - Blame information for rev 246

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1 246 jshamlet
-- Copyright (c)2006, 2016, 2019, 2020 Jeremy Seth Henry
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-- All rights reserved.
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--
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-- Redistribution and use in source and binary forms, with or without
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-- modification, are permitted provided that the following conditions are met:
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--     * Redistributions of source code must retain the above copyright
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--       notice, this list of conditions and the following disclaimer.
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--     * Redistributions in binary form must reproduce the above copyright
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--       notice, this list of conditions and the following disclaimer in the
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--       documentation and/or other materials provided with the distribution,
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--       where applicable (as part of a user interface, debugging port, etc.)
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--
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-- THIS SOFTWARE IS PROVIDED BY JEREMY SETH HENRY ``AS IS'' AND ANY
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-- EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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-- WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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-- DISCLAIMED. IN NO EVENT SHALL JEREMY SETH HENRY BE LIABLE FOR ANY
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-- DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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-- (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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-- LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
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-- ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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-- (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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-- THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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--
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-- VHDL Units :  o8_sys_timer
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-- Description:  Provides an 8-bit microsecond resolution timer for generating
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--            :   periodic interrupts for the Open8 CPU.
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--
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--
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-- Revision History
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-- Author          Date     Change
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------------------ -------- ---------------------------------------------------
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-- Seth Henry      07/28/11 Design Start
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-- Seth Henry      12/19/19 Renamed Tmr_Out to Interrupt
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-- Seth Henry      04/09/20 Modified timer update logic to reset the timer on
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--                           interval write.
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-- Seth Henry      04/16/20 Modified to use Open8 bus record
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-- Seth Henry      05/18/20 Added write qualification input
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library ieee;
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use ieee.std_logic_1164.all;
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  use ieee.std_logic_unsigned.all;
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  use ieee.std_logic_arith.all;
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  use ieee.std_logic_misc.all;
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library work;
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  use work.open8_pkg.all;
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entity o8_sys_timer is
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generic(
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  mSec_Resolution            : boolean := FALSE;
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  Address                    : ADDRESS_TYPE
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);
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port(
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  Open8_Bus                  : in  OPEN8_BUS_TYPE;
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  Write_Qual                 : in  std_logic := '1';
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  Rd_Data                    : out DATA_TYPE;
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  Interrupt                  : out std_logic
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);
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end entity;
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architecture behave of o8_sys_timer is
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  alias Clock                is Open8_Bus.Clock;
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  alias Reset                is Open8_Bus.Reset;
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  alias uSec_Tick            is Open8_Bus.uSec_Tick;
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  constant User_Addr         : ADDRESS_TYPE := Address;
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  alias  Comp_Addr           is Open8_Bus.Address(15 downto 0);
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  signal Addr_Match          : std_logic := '0';
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  signal Wr_En_d             : std_logic;
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  signal Wr_En_q             : std_logic := '0';
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  alias  Wr_Data_d           is Open8_Bus.Wr_Data;
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  signal Wr_Data_q           : DATA_TYPE := x"00";
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  signal Rd_En_d               : std_logic := '0';
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  signal Rd_En_q             : std_logic := '0';
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  signal Interval            : DATA_TYPE := x"00";
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  signal Update_Interval     : std_logic;
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  signal Timer_Cnt           : DATA_TYPE := x"00";
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  constant MSEC_DELAY        : std_logic_vector(9 downto 0) :=
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                                conv_std_logic_vector(1000,10);
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  signal mSec_Timer          : std_logic_vector(9 downto 0) := (others => '0');
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  signal Timer_Tick          : std_logic := '0';
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begin
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  Addr_Match                 <= '1' when Comp_Addr = User_Addr else '0';
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  Wr_En_d                    <= Addr_Match and Open8_Bus.Wr_En;
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  Rd_En_d                    <= Addr_Match and Open8_Bus.Rd_En;
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mSec_Resolution_enabled : if( mSec_Resolution )generate
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  mSec_Tick_proc: process( Clock, Reset )
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  begin
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    if( Reset = Reset_Level )then
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      mSec_Timer             <= (others => '0');
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      Timer_Tick             <= '0';
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    elsif( rising_edge(Clock) )then
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      mSec_Timer             <= mSec_Timer - uSec_Tick;
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      Timer_Tick             <= '0';
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      if( mSec_Timer = 0 )then
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        mSec_Timer           <= MSEC_DELAY;
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        Timer_Tick           <= '1';
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      end if;
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    end if;
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  end process;
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end generate;
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uSec_Resolution_enabled : if( not mSec_Resolution )generate
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  Timer_Tick                 <= uSec_Tick;
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end generate;
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  io_reg: process( Clock, Reset )
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  begin
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    if( Reset = Reset_Level )then
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      Wr_En_q                <= '0';
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      Wr_Data_q              <= x"00";
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      Rd_En_q                <= '0';
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      Rd_Data                <= OPEN8_NULLBUS;
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      Interval               <= x"00";
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      Update_Interval        <= '0';
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    elsif( rising_edge( Clock ) )then
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      Wr_En_q                <= Wr_En_d;
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      Wr_Data_q              <= Wr_Data_d;
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      Update_Interval        <= Wr_En_q and Write_Qual;
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      if( Wr_En_q = '1' and Write_Qual = '1' )then
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        Interval             <= Wr_Data_q;
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      end if;
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      Rd_Data                <= (others => '0');
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      Rd_En_q                <= Rd_En_d;
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      if( Rd_En_q = '1' )then
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        Rd_Data              <= Interval;
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      end if;
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    end if;
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  end process;
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  Interval_proc: process( Clock, Reset )
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  begin
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    if( Reset = Reset_Level )then
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      Timer_Cnt              <= x"00";
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      Interrupt              <= '0';
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    elsif( rising_edge(Clock) )then
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      Interrupt              <= '0';
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      Timer_Cnt              <= Timer_Cnt - Timer_Tick;
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      if( Update_Interval = '1' )then
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        Timer_Cnt            <= Interval;
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      elsif( or_reduce(Timer_Cnt) = '0' )then
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        Timer_Cnt            <= Interval;
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        Interrupt            <= or_reduce(Interval); -- Only trigger on Int > 0
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      end if;
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    end if;
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  end process;
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end architecture;

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