Added VME watchdog

src/vme_watchdog.vhd

+library ieee;
+use ieee.std_logic_1164.all;
+use work.vme_pkg.all;
+
+entity vme_watchdog is
+  port (
+    signal clk      : in std_logic;
+
+    signal vme_as_n_i                 : in std_logic;
+    signal vme_berr_n_o               : out std_logic := '0';
+    signal vme_berr_n_dir             : out std_logic := c_PIN_IN
+    
+    );
+end entity;
+
+architecture rtl of vme_watchdog is
+  constant CNT_MAX : integer := 255;
+  signal cnt : integer range 0 to 255 := CNT_MAX;
+begin
+
+  process (clk)
+  begin
+    if (rising_edge(clk)) then
+      if vme_as_n_i = '0' then
+        if cnt = 0 then
+          vme_berr_n_o <= '0';
+          vme_berr_n_dir <= c_PIN_OUT;
+        else
+          cnt <= cnt - 1;
+        end if;
+      else
+          vme_berr_n_o <= '1';
+          vme_berr_n_dir <= c_PIN_IN;
+          cnt <= CNT_MAX;
+      end if;
+    end if;
+  end process;  
+end architecture;  
+