Subversion Repositories neorv32

-- #################################################################################################
-- # << NEORV32 - Watch Dog Timer (WDT) >>                                                         #
-- # ********************************************************************************************* #
-- # The internal counter is 20 bit wide and increases using 1 out of 8 available clock            #
-- # prescalers. When the counter overflows, either a hardware reset (mode = 1) is performed or an #
-- # interrupt (mode = 0) is triggered. 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). For a write access with a wrong password           #
-- # a HW reset or IRQ (depending on mode) 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 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
 
  -- Watchdog access password --
  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_mode_c    : natural := 4; -- r/w: 0: timeout causes interrupt, 1: timeout causes hard reset
  constant ctrl_cause_c   : natural := 5; -- r/-: action (reset/IRQ) cause (0: external, 1: watchdog)
  constant ctrl_pwfail_c  : natural := 6; -- r/-: watchdog action (reset/IRQ) 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 source  : std_ulogic; -- source of wdt action: '0' = external, '1' = watchdog
  signal pw_fail : std_ulogic; -- watchdog action caused by wrong password access
  signal enable  : std_ulogic;
  signal mode    : std_ulogic;
  signal clk_sel : std_ulogic_vector(02 downto 0);
 
  -- reset counter --
  signal cnt      : std_ulogic_vector(20 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 (rstn_i = '0') or (rst_sync(1) = '0') then -- external or internal reset
        enable  <= '0'; -- disable WDT
        mode    <= '0'; -- trigger interrupt if watchdog timeouts
        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);
          mode    <= data_i(ctrl_mode_c);
        end if;
        -- trigger system reset when enabled AND reset mode AND timeout OR unauthorized access --
        if (enable = '1') and (mode = '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);
      -- IRQ mode --
      irq_o <= '0';
      if (enable = '1') and (mode = '0') and ((cnt(cnt'left) = '1') or (fail_ff = '1')) then
        irq_o <= '1'; -- trigger interrupt if watchdog timeout and MODE=0
      end if;
      -- 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 --
  rstn_o <= rst_sync(1);
 
 
  -- Reset Cause Indicator ------------------------------------------------------------------
  -- -------------------------------------------------------------------------------------------
  rst_cause: process(rstn_i, clk_i)
  begin
    if (rstn_i = '0') then
      source  <= '0';
      pw_fail <= '0';
    elsif rising_edge(clk_i) then
      source  <= 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
    end if;
  end process rst_cause;
 
 
  -- Read Access ----------------------------------------------------------------------------
  -- -------------------------------------------------------------------------------------------
  read_access: process(clk_i)
  begin
    if rising_edge(clk_i) then
      ack_o  <= acc_en and (rden_i or wren_i);
      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_cause_c)  <= source;
        data_o(ctrl_pwfail_c) <= pw_fail;
        data_o(ctrl_mode_c)   <= mode;
      end if;
    end if;
  end process read_access;
 
 
end neorv32_wdt_rtl;