feat: add rtl/fault_filter.vhd

rtl/fault_filter.vhd

@@ -0,0 +1,15 @@
+library ieee;
+use ieee.std_logic_1164.all;
+
+entity fault_filter is
+  port (valid : in std_logic;
+        mask_in : in std_logic_vector(2 downto 0);
+        mask_out : out std_logic_vector(2 downto 0);
+        any_fault : out std_logic);
+end entity;
+
+architecture rtl of fault_filter is
+begin
+  mask_out <= mask_in when valid = '1' else (others => '0');
+  any_fault <= (mask_in(0) or mask_in(1) or mask_in(2)) and valid;
+end architecture;