Subversion Repositories neorv32

-- #################################################################################################

-- # << NEORV32 - General Purpose Timer (GPTMR) >>                                                 #

-- # ********************************************************************************************* #

-- # 32-bit timer with configurable clock prescaler. The timer fires an interrupt whenever the     #

-- # counter register value reaches the programmed threshold value. The timer can operate in       #

-- # single-shot mode (count until it reaches THRESHOLD and stop) or in continuous mode (count     #

-- # until it reaches THRESHOLD and auto-reset).                                                   #

-- # ********************************************************************************************* #

-- # BSD 3-Clause License                                                                          #

-- #                                                                                               #

-- # Copyright (c) 2021, Stephan Nolting. All rights reserved.                                     #

-- #                                                                                               #

-- # Redistribution and use in source and binary forms, with or without modification, are          #

-- # permitted provided that the following conditions are met:                                     #

-- #                                                                                               #

-- # 1. Redistributions of source code must retain the above copyright notice, this list of        #

-- #    conditions and the following disclaimer.                                                   #

-- #                                                                                               #

-- # 2. 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.                                                            #

-- #                                                                                               #

-- # 3. Neither the name of the copyright holder nor the names of its contributors may be used to  #

-- #    endorse or promote products derived from this software without specific prior written      #

-- #    permission.                                                                                #

-- #                                                                                               #

-- # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "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 THE    #

-- # COPYRIGHT HOLDER OR CONTRIBUTORS 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.                                                            #

-- # ********************************************************************************************* #

-- # The NEORV32 Processor - https://github.com/stnolting/neorv32              (c) Stephan Nolting #

-- #################################################################################################

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

library neorv32;

use neorv32.neorv32_package.all;

entity neorv32_gptmr is

  port (

    -- host access --

    clk_i       : in  std_ulogic; -- global clock line

    addr_i      : in  std_ulogic_vector(31 downto 0); -- address

    rden_i      : in  std_ulogic; -- read enable

    wren_i      : in  std_ulogic; -- write enable

    data_i      : in  std_ulogic_vector(31 downto 0); -- data in

    data_o      : out std_ulogic_vector(31 downto 0); -- data out

    ack_o       : out std_ulogic; -- transfer acknowledge

    -- clock generator --

    clkgen_en_o : out std_ulogic; -- enable clock generator

    clkgen_i    : in  std_ulogic_vector(07 downto 0);

    -- interrupt --

    irq_o       : out std_ulogic -- transmission done interrupt

  );

end neorv32_gptmr;

architecture neorv32_gptmr_rtl of neorv32_gptmr is

  -- IO space: module base address --

  constant hi_abb_c : natural := index_size_f(io_size_c)-1; -- high address boundary bit

  constant lo_abb_c : natural := index_size_f(gptmr_size_c); -- low address boundary bit

  -- control register --

  constant ctrl_en_c    : natural := 0; -- r/w: timer enable

  constant ctrl_prsc0_c : natural := 1; -- r/w: clock prescaler select bit 0

  constant ctrl_prsc1_c : natural := 2; -- r/w: clock prescaler select bit 1

  constant ctrl_prsc2_c : natural := 3; -- r/w: clock prescaler select bit 2

  constant ctrl_mode_c  : natural := 4; -- r/w: mode (0=single-shot, 1=continuous)

  constant ctrl_alarm_c : natural := 5; -- r/c: alarm flag (interrupt), cleared by writing zero

  --

  signal ctrl : std_ulogic_vector(4 downto 0);

  -- access control --

  signal acc_en : std_ulogic; -- module access enable

  signal addr   : std_ulogic_vector(31 downto 0); -- access address

  signal wren   : std_ulogic; -- word write enable

  signal rden   : std_ulogic; -- read enable

  -- clock generator --

  signal gptmr_clk_en : std_ulogic;

  -- timer core --

  type timer_t is record

    count  : std_ulogic_vector(31 downto 0); -- counter register

    thres  : std_ulogic_vector(31 downto 0); -- threshold value

    match  : std_ulogic; -- count == thres

    cnt_we : std_ulogic; -- write access to count

  end record;

  signal timer : timer_t;

  -- interrupt generator --

  type irq_t is record

    pending : std_ulogic; -- pending interrupt request

    detect  : std_ulogic_vector(1 downto 0); -- rising-edge detector

    clearn  : std_ulogic; -- clear/ack IRQ request, active-low

  end record;

  signal irq : irq_t;

begin

  -- Access Control -------------------------------------------------------------------------

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

  acc_en <= '1' when (addr_i(hi_abb_c downto lo_abb_c) = gptmr_base_c(hi_abb_c downto lo_abb_c)) else '0';

  addr   <= gptmr_base_c(31 downto lo_abb_c) & addr_i(lo_abb_c-1 downto 2) & "00"; -- word aligned

  wren   <= acc_en and wren_i;

  rden   <= acc_en and rden_i;

  -- Read/Write Access ----------------------------------------------------------------------

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

  rw_access: process(clk_i)

  begin

    if rising_edge(clk_i) then

      -- bus access acknowledge --

      ack_o <= rden or wren;

      -- write access --

      irq.clearn   <= '1';

      timer.cnt_we <= '0';

      if (wren = '1') then

        if (addr = gptmr_ctrl_addr_c) then -- control register

          ctrl(ctrl_en_c)    <= data_i(ctrl_en_c);

          ctrl(ctrl_prsc0_c) <= data_i(ctrl_prsc0_c);

          ctrl(ctrl_prsc1_c) <= data_i(ctrl_prsc1_c);

          ctrl(ctrl_prsc2_c) <= data_i(ctrl_prsc2_c);

          ctrl(ctrl_mode_c)  <= data_i(ctrl_mode_c);

          irq.clearn         <= data_i(ctrl_alarm_c);

        end if;

        if (addr = gptmr_thres_addr_c) then -- threshold register

          timer.thres <= data_i;

        end if;

        if (addr = gptmr_count_addr_c) then -- counter register

          timer.cnt_we <= '1';

        end if;

      end if;

      -- read access --

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

      if (rden = '1') then

        case addr(3 downto 2) is

          when "00" => -- control register

            data_o(ctrl_en_c)    <= ctrl(ctrl_en_c);

            data_o(ctrl_prsc0_c) <= ctrl(ctrl_prsc0_c);

            data_o(ctrl_prsc1_c) <= ctrl(ctrl_prsc1_c);

            data_o(ctrl_prsc2_c) <= ctrl(ctrl_prsc2_c);

            data_o(ctrl_mode_c)  <= ctrl(ctrl_mode_c);

            data_o(ctrl_alarm_c) <= irq.pending;

          when "01" => -- threshold register

            data_o <= timer.thres;

          when others => -- counter register

            data_o <= timer.count;

        end case;

      end if;

    end if;

  end process rw_access;

  -- clock generator enable --

  clkgen_en_o <= ctrl(ctrl_en_c);

  -- clock select --

  gptmr_clk_en <= clkgen_i(to_integer(unsigned(ctrl(ctrl_prsc2_c downto ctrl_prsc0_c))));

  -- Timer Core -----------------------------------------------------------------------------

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

  timer_core: process(clk_i)

  begin

    if rising_edge(clk_i) then

      if (timer.cnt_we = '1') then -- write access

        timer.count <= data_i;

      elsif (ctrl(ctrl_en_c) = '1') and (gptmr_clk_en = '1') then -- enabled and clock tick

        if (timer.match = '1') then

          if (ctrl(ctrl_mode_c) = '1') then -- reset counter if continuous mode

            timer.count <= (others => '0');

          end if;

        else

          timer.count <= std_ulogic_vector(unsigned(timer.count) + 1);

        end if;

      end if;

    end if;

  end process timer_core;

  -- counter = threshold? --

  timer.match <= '1' when (timer.count = timer.thres) else '0';

  -- Interrupt Generator --------------------------------------------------------------------

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

  irq_generator: process(clk_i)

  begin

    if rising_edge(clk_i) then

      if (ctrl(ctrl_en_c) = '0') then

        irq.detect  <= "00";

        irq.pending <= '0';

      else

        irq.detect <= irq.detect(0) & timer.match;

        if (irq.detect = "01") then -- rising edge

          irq.pending <= '1';

        elsif (irq.clearn = '0') then

          irq.pending <= '0';

        end if;

      end if;

    end if;

  end process irq_generator;

  -- IRQ request to CPU --

  irq_o <= irq.pending;

end neorv32_gptmr_rtl;