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[/] [open8_urisc/] [trunk/] [VHDL/] [o8_epoch_timer.vhd] - Blame information for rev 189

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Line No. Rev Author Line
1 189 jshamlet
-- Copyright (c)2011, 2019 Jeremy Seth Henry
2 170 jshamlet
-- 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 THIS
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-- SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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--
24 184 jshamlet
-- VHDL Units :  o8_epoch_timer
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-- Description:  Provides a 24-bit, 4uS resolution elapsed timer with
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--            :   alarm and interrupt for the Open8 CPU.
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--
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-- Notes      :  Requires an externally provided uSec tick input - one clock
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--            :   per microsecond.
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--
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-- Register Map:
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-- Offset  Bitfield Description                        Read/Write
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--   0x0   AAAAAAAA B0 of Setpoint (W) or Buffered Time(R)
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--   0x1   AAAAAAAA B1 of Setpoint (W) or Buffered Time(R)
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--   0x2   AAAAAAAA B2 of Setpoint (W) or Buffered Time(R)
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--   0x3   C-----BA Control/Status register (RW)
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--                  A = Update Buffered Time from internal timer (W)
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--                  B = Reset Internal Epoch Time (W)
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--                  C = Alarm State Flag (RW) (write a 1 to clear)
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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 to "o8_epoch_timer" to fit "theme"
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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_epoch_timer is
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generic(
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  Reset_Level           : std_logic;
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  Address               : ADDRESS_TYPE
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);
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port(
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  Clock                 : in  std_logic;
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  Reset                 : in  std_logic;
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  uSec_Tick             : in  std_logic;
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  --
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  Bus_Address           : in  ADDRESS_TYPE;
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  Wr_Enable             : in  std_logic;
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  Wr_Data               : in  DATA_TYPE;
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  Rd_Enable             : in  std_logic;
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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_epoch_timer is
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  constant User_Addr    : std_logic_vector(15 downto 2)
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                          := Address(15 downto 2);
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  alias  Comp_Addr      is Bus_Address(15 downto 2);
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  signal Addr_Match     : std_logic;
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  alias  Reg_Addr       is Bus_Address(1 downto 0);
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  signal Reg_Addr_q     : std_logic_vector(1 downto 0);
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  signal Wr_En          : std_logic;
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  signal Wr_Data_q      : DATA_TYPE;
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  signal Rd_En          : std_logic;
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  signal epoch_tmr      : std_logic_vector(25 downto 0);
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  alias  epoch_tmrcmp   is epoch_tmr(25 downto 2);
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  signal epoch_buffer   : std_logic_vector(23 downto 0);
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  signal epoch_setpt    : std_logic_vector(25 downto 0);
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  signal epoch_alarm    : std_logic;
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  signal epoch_alarm_q  : std_logic;
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begin
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  Addr_Match            <= '1' when Comp_Addr = User_Addr else '0';
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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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      epoch_tmr         <= (others => '0');
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      epoch_buffer      <= (others => '0');
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      epoch_setpt       <= (others => '0');
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      epoch_alarm       <= '0';
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      epoch_alarm_q     <= '0';
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      Wr_Data_q         <= (others => '0');
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      Reg_Addr_q        <= (others => '0');
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      Wr_En             <= '0';
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      Rd_En             <= '0';
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      Rd_Data           <= (others => '0');
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      Interrupt         <= '0';
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    elsif( rising_edge( Clock ) )then
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      epoch_tmr         <= epoch_tmr + uSec_Tick;
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                -- Force the lower bits of the setpoint to "11" so that the offset is
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                --  reduced to 1uS (reproducing the original behavior). Software should
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                --  always subtract 4uS (-1) from the desired time to compensate
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                epoch_setpt(1 downto 0) <= "11";
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      Reg_Addr_q        <= Reg_Addr;
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      Wr_Data_q         <= Wr_Data;
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      Wr_En             <= Addr_Match and Wr_Enable;
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      if( Wr_En = '1' and or_reduce(Reg_Addr_q) = '0' )then
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        epoch_buffer    <= epoch_tmrcmp(25 downto 2);
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      end if;
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      if( Wr_En = '1' )then
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        case( Reg_Addr_q )is
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          when "00" =>
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            epoch_setpt(9 downto 2)   <= Wr_Data_q;
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          when "01" =>
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            epoch_setpt(17 downto 10) <= Wr_Data_q;
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          when "10" =>
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            epoch_setpt(25 downto 18) <= Wr_Data_q;
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          when "11" =>
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            if( Wr_Data_q(0) = '1' )then
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              epoch_buffer            <= epoch_tmrcmp;
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            end if;
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            if( Wr_Data_q(1) = '1' )then
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              epoch_tmr               <= (others => '0');
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            end if;
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            if( Wr_Data_q(7) = '1' )then
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              epoch_alarm             <= '0';
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            end if;
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          when others => null;
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        end case;
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      end if;
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      -- Set and hold on alarm condition
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      if( epoch_tmr > epoch_setpt )then
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        epoch_alarm     <= '1';
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      end if;
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      epoch_alarm_q     <= epoch_alarm;
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      -- Fire on rising edge of epoch_alarm
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      Interrupt         <= epoch_alarm and not epoch_alarm_q;
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      Rd_Data           <= (others => '0');
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      Rd_En             <= Addr_Match and Rd_Enable;
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      if( Rd_En = '1' )then
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        case( Reg_Addr_q )is
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          when "00" =>
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            Rd_Data     <= epoch_buffer(7 downto 0);
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          when "01" =>
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            Rd_Data     <= epoch_buffer(15 downto 8);
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          when "10" =>
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            Rd_Data     <= epoch_buffer(23 downto 16);
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          when "11" =>
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            Rd_Data     <= epoch_alarm & "0000000";
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          when others => null;
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        end case;
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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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