Subversion Repositories neo430

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

-- # << NEO430 - Watchdog Timer >>                                                                 #

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

-- # The internal counter is 16 bit wide and triggers a HW reset when overflowing. The clock is    #

-- # selected via the clk_sel bits of the control register. The WDT can only operate when the      #

-- # enable bit is set. A write access to the WDT can only be performed, if the higher byte of the #

-- # written data contains the specific WDT password (0x47). I a write access occurs with a wrong  #

-- # password, a HW reset is triggered, but only if the WDT is enabled.                            #

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

-- # BSD 3-Clause License                                                                          #

-- #                                                                                               #

-- # Copyright (c) 2020, 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 NEO430 Processor - https://github.com/stnolting/neo430                                    #

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

library neo430;

use neo430.neo430_package.all;

entity neo430_wdt is

  port (

    -- host access --

    clk_i       : in  std_ulogic; -- global clock line

    rst_i       : in  std_ulogic; -- external reset, low-active, use as async

    rden_i      : in  std_ulogic; -- read enable

    wren_i      : in  std_ulogic; -- write enable

    addr_i      : in  std_ulogic_vector(15 downto 0); -- address

    data_i      : in  std_ulogic_vector(15 downto 0); -- data in

    data_o      : out std_ulogic_vector(15 downto 0); -- data out

    -- clock generator --

    clkgen_en_o : out std_ulogic; -- enable clock generator

    clkgen_i    : in  std_ulogic_vector(07 downto 0);

    -- system reset --

    rst_o       : out std_ulogic -- timeout reset, low_active, use it as async!

  );

end neo430_wdt;

architecture neo430_wdt_rtl of neo430_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

  -- Watchdog access password - do not change! --

  constant wdt_password_c : std_ulogic_vector(07 downto 0) := x"47";

  -- Control register bits --

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

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

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

  constant ctrl_enable_c  : natural := 3; -- r/w: WDT enable

  constant ctrl_rcause_c  : natural := 4; -- r/-: reset cause (0: external, 1: watchdog timeout)

  constant ctrl_rpwfail_c : natural := 5; -- r/-: watchdog reset caused by wrong password access when '1'

  -- access control --

  signal acc_en        : std_ulogic; -- module access enable

  signal pwd_ok        : std_ulogic; -- password correct

  signal fail, fail_ff : std_ulogic; -- unauthorized access

  signal wren          : std_ulogic;

  -- accessible regs --

  signal rst_source : std_ulogic; -- source of the system reset: '0' = external, '1' = watchdog timeout

  signal pw_fail    : std_ulogic; -- watchdog reset caused by wrong password access

  signal enable     : std_ulogic;

  signal clk_sel    : std_ulogic_vector(02 downto 0);

  -- reset counter --

  signal cnt      : std_ulogic_vector(16 downto 0);

  signal rst_gen  : std_ulogic_vector(03 downto 0);

  signal rst_sync : std_ulogic_vector(01 downto 0);

  -- prescaler clock generator --

  signal prsc_tick : std_ulogic;

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';

  pwd_ok <= '1' when (data_i(15 downto 8) = wdt_password_c) else '0'; -- password check

  wren   <= '1' when ((acc_en = '1') and (wren_i = '1') and (pwd_ok = '1')) else '0'; -- write access ok

  fail   <= '1' when ((acc_en = '1') and (wren_i = '1') and (pwd_ok = '0')) else '0'; -- write access fail!

  -- Write Access, Reset Generator --------------------------------------------

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

  wdt_core: process(clk_i)

  begin

    if rising_edge(clk_i) then

      if (rst_i = '0') or (rst_sync(1) = '0') then -- external or internal reset

        enable  <= '0'; -- disable WDT

        clk_sel <= (others => '1'); -- slowest clock rst_source

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

      else

        -- control register write access --

        if (wren = '1') then -- allow write if password is correct

          enable  <= data_i(ctrl_enable_c);

          clk_sel <= data_i(ctrl_clksel2_c downto ctrl_clksel0_c);

        end if;

        -- reset generator - enabled and (overflow or unauthorized access)? --

        if (enable = '1') and ((cnt(cnt'left) = '1') or (fail_ff = '1')) then

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

        else

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

        end if;

      end if;

    end if;

  end process wdt_core;

  -- enable external clock generator --

  clkgen_en_o <= enable;

  -- Counter Update -----------------------------------------------------------

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

  cnt_sync: process(clk_i)

  begin

    if rising_edge(clk_i) then

      -- clock_en buffer --

      prsc_tick <= clkgen_i(to_integer(unsigned(clk_sel)));

      -- unauthorized access buffer --

      fail_ff <= fail;

      -- reset synchronizer --

      rst_sync <= rst_sync(0) & rst_gen(rst_gen'left);

      -- counter update --

      if (wren = '1') then -- clear counter on write access (manual watchdog reset)

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

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

        cnt <= std_ulogic_vector(unsigned('0' & cnt(cnt'left-1 downto 0)) + 1);

      end if;

    end if;

  end process cnt_sync;

  -- system reset --

  rst_o <= rst_sync(1);

  -- Reset Cause Indicator ----------------------------------------------------

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

  rst_cause: process(rst_i, clk_i)

  begin

    if (rst_i = '0') then

      rst_source <= '0';

      pw_fail    <= '0';

    elsif rising_edge(clk_i) then

      rst_source <= rst_source or (cnt(cnt'left) and enable) or (fail_ff and enable); -- set on WDT timeout or access error

      pw_fail    <= (pw_fail or (fail_ff and enable)) and (not (cnt(cnt'left) and enable)); -- set on failed access, clear on WDT timeout

    --pw_fail    <= (pw_fail and (not (cnt(cnt'left) and enable))) or (fail_ff and enable); -- clear on WDT timeout, set on failed access

    end if;

  end process rst_cause;

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

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

  read_access: process(clk_i)

  begin

    if rising_edge(clk_i) then

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

      if (acc_en = '1') and (rden_i = '1') then

        data_o(ctrl_clksel2_c downto ctrl_clksel0_c) <= clk_sel;

        data_o(ctrl_enable_c)  <= enable;

        data_o(ctrl_rcause_c)  <= rst_source;

        data_o(ctrl_rpwfail_c) <= pw_fail;

      end if;

    end if;

  end process read_access;

end neo430_wdt_rtl;