Subversion Repositories neorv32

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

-- # << NEORV32 - Watch Dog Timer (WDT) >>                                                         #

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

-- # Watchdog counter to trigger an action if the CPU gets stuck.                                  #

-- # The internal counter is 20-bit wide. If this counter overflows one of two possible actions is #

-- # triggered: Generate an IRQ or force a hardware reset of the system.                           #

-- # A WDT action can also be triggered manually at any time by setting the FORCE bit.             #

-- #                                                                                               #

-- # Access to the control register can be permanently locked by setting the lock bit. This bit    #

-- # can only be cleared by a hardware reset (external or caused by the watchdog itself).          #

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

-- # 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_wdt is

  port (

    -- host access --

    clk_i       : in  std_ulogic; -- global clock line

    rstn_i      : in  std_ulogic; -- global reset line, low-active

    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);

    -- timeout event --

    irq_o       : out std_ulogic; -- timeout IRQ

    rstn_o      : out std_ulogic  -- timeout reset, low_active, use as async

  );

end neorv32_wdt;

architecture neorv32_wdt_rtl of neorv32_wdt 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(wdt_size_c); -- low address boundary bit

  -- Control register bits --

  constant ctrl_enable_c  : natural := 0; -- r/w: WDT enable

  constant ctrl_clksel0_c : natural := 1; -- r/w: prescaler select bit 0

  constant ctrl_clksel1_c : natural := 2; -- r/w: prescaler select bit 1

  constant ctrl_clksel2_c : natural := 3; -- r/w: prescaler select bit 2

  constant ctrl_mode_c    : natural := 4; -- r/w: 0: WDT timeout triggers interrupt, 1: WDT timeout triggers hard reset

  constant ctrl_rcause_c  : natural := 5; -- r/-: cause of last action (reset/IRQ): 0=external reset, 1=watchdog overflow

  constant ctrl_reset_c   : natural := 6; -- -/w: reset WDT if set

  constant ctrl_force_c   : natural := 7; -- -/w: force WDT action

  constant ctrl_lock_c    : natural := 8; -- r/w: lock access to control register when set

  -- access control --

  signal acc_en : std_ulogic; -- module access enable

  signal wren   : std_ulogic;

  signal rden   : std_ulogic;

  -- control register --

  type ctrl_reg_t is record

    enable  : std_ulogic; -- 1=WDT enabled

    clk_sel : std_ulogic_vector(2 downto 0);

    mode    : std_ulogic; -- 0=trigger IRQ on overflow; 1=trigger hard reset on overflow

    rcause  : std_ulogic; -- cause of last system reset: '0' = external, '1' = watchdog

    reset   : std_ulogic; -- reset WDT

    enforce : std_ulogic; -- force action

    lock    : std_ulogic; -- lock control register

  end record;

  signal ctrl_reg : ctrl_reg_t;

  -- prescaler clock generator --

  signal prsc_tick : std_ulogic;

  -- WDT core --

  signal wdt_cnt : std_ulogic_vector(20 downto 0);

  signal hw_rst  : std_ulogic;

  signal rst_gen : std_ulogic_vector(03 downto 0);

  -- internal reset (sync, low-active) --

  signal rstn_sync : std_ulogic;

  -- cpu interrupt --

  type cpu_irq_t is record

    pending : std_ulogic;

    set     : std_ulogic;

    clr     : std_ulogic;

  end record;

  signal cpu_irq : cpu_irq_t;

begin

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

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

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

  wren   <= acc_en and wren_i;

  rden   <= acc_en and rden_i;

  -- Write Access ---------------------------------------------------------------------------

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

  write_access: process(rstn_i, clk_i)

  begin

    if (rstn_i = '0') then

      ctrl_reg.reset   <= '0';

      ctrl_reg.enforce <= '0';

      ctrl_reg.enable  <= '0'; -- disable WDT

      ctrl_reg.mode    <= '0'; -- trigger interrupt on WDT overflow

      ctrl_reg.clk_sel <= (others => '1'); -- slowest clock source

      ctrl_reg.lock    <= '0';

    elsif rising_edge(clk_i) then

      -- acknowledge interrupt when resetting WDT --

      if (rstn_sync = '0') then -- internal reset

        ctrl_reg.reset   <= '0';

        ctrl_reg.enforce <= '0';

        ctrl_reg.enable  <= '0'; -- disable WDT

        ctrl_reg.mode    <= '0'; -- trigger interrupt on WDT overflow

        ctrl_reg.clk_sel <= (others => '1'); -- slowest clock source

        ctrl_reg.lock    <= '0';

      else

        -- auto-clear WDT reset and WDT force flags --

        ctrl_reg.reset   <= '0';

        ctrl_reg.enforce <= '0';

        -- actual write access --

        if (wren = '1') then

          ctrl_reg.reset   <= data_i(ctrl_reset_c);

          ctrl_reg.enforce <= data_i(ctrl_force_c);

          if (ctrl_reg.lock = '0') then -- update configuration only if unlocked

            ctrl_reg.enable  <= data_i(ctrl_enable_c);

            ctrl_reg.mode    <= data_i(ctrl_mode_c);

            ctrl_reg.clk_sel <= data_i(ctrl_clksel2_c downto ctrl_clksel0_c);

            ctrl_reg.lock    <= data_i(ctrl_lock_c);

          end if;

        end if;

      end if;

    end if;

  end process write_access;

  -- clock generator --

  clkgen_en_o <= ctrl_reg.enable; -- enable clock generator

  prsc_tick   <= clkgen_i(to_integer(unsigned(ctrl_reg.clk_sel))); -- clock enable tick

  -- Watchdog Counter -----------------------------------------------------------------------

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

  wdt_counter: process(clk_i)

  begin

    if rising_edge(clk_i) then

      if (ctrl_reg.reset = '1') then -- watchdog reset

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

      elsif (ctrl_reg.enable = '1') and (prsc_tick = '1') then

        wdt_cnt <= std_ulogic_vector(unsigned(wdt_cnt) + 1);

      end if;

    end if;

  end process wdt_counter;

  -- action trigger --

  cpu_irq.set <= ctrl_reg.enable and (wdt_cnt(wdt_cnt'left) or ctrl_reg.enforce) and (not ctrl_reg.mode); -- mode 0: IRQ

  cpu_irq.clr <= ctrl_reg.reset; -- ack IRQ on WDT reset

  hw_rst      <= ctrl_reg.enable and (wdt_cnt(wdt_cnt'left) or ctrl_reg.enforce) and (    ctrl_reg.mode); -- mode 1: RESET

  -- Interrupt ------------------------------------------------------------------------------

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

  irq_gen: process(clk_i)

  begin

    if rising_edge(clk_i) then

      if (ctrl_reg.enable = '0') then

        cpu_irq.pending <= '0';

      else

        if (cpu_irq.set = '1') then

          cpu_irq.pending <= '1';

        elsif(cpu_irq.clr = '1') then

          cpu_irq.pending <= '0';

        else

          cpu_irq.pending <= cpu_irq.pending;

        end if;

      end if;

    end if;

  end process irq_gen;

  -- CPU IRQ --

  irq_o <= cpu_irq.pending;

  -- Reset Generator & Action Cause Indicator -----------------------------------------------

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

  reset_generator: process(rstn_i, clk_i)

  begin

    if (rstn_i = '0') then

      ctrl_reg.rcause <= '0';

      rst_gen         <= (others => '1'); -- do NOT fire on reset!

      rstn_sync       <= '1';

    elsif rising_edge(clk_i) then

      ctrl_reg.rcause <= ctrl_reg.rcause or hw_rst; -- sticky-set on WDT timeout/force

      if (hw_rst = '1') then

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

      else

        rst_gen <= rst_gen(rst_gen'left-1 downto 0) & '1';

      end if;

      rstn_sync <= rst_gen(rst_gen'left);

    end if;

  end process reset_generator;

  -- system reset --

  rstn_o <= rst_gen(rst_gen'left);

  -- Read Access ----------------------------------------------------------------------------

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

  read_access: process(clk_i)

  begin

    if rising_edge(clk_i) then

      ack_o  <= rden or wren;

      if (rden = '1') then

        data_o(ctrl_enable_c) <= ctrl_reg.enable;

        data_o(ctrl_mode_c)   <= ctrl_reg.mode;

        data_o(ctrl_rcause_c) <= ctrl_reg.rcause;

        data_o(ctrl_clksel2_c downto ctrl_clksel0_c) <= ctrl_reg.clk_sel;

        data_o(ctrl_lock_c)   <= ctrl_reg.lock;

      else

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

      end if;

    end if;

  end process read_access;

end neorv32_wdt_rtl;