library IEEE; use IEEE.std_logic_1164.all; package logic_pack is function resolve(s : std_ulogic_vector) return std_ulogic; SUBTYPE logic is resolve std_ulogic; TYPE logic_vector IS ARRAY (NATURAL RANGE ) OF logic; TYPE std_logic_array IS ARRAY (NATURAL RANGE ,NATURAL RANGE ) OF std_logic; end logic_pack; package body logic_pack is TYPE stdlogic_table IS ARRAY(std_ulogic, std_ulogic) OF std_ulogic; ------------------------------------------------------------------- -- resolution function ------------------------------------------------------------------- CONSTANT resolve_table : stdlogic_table := ( -- --------------------------------------------------------- -- | U X 0 1 Z W L H - | | -- --------------------------------------------------------- ( 'U', 'U', 'U', 'U', 'U', 'U', 'U', 'U', 'U' ), -- | U | ( 'U', 'X', 'X', 'X', 'X', 'X', 'X', 'X', 'X' ), -- | X | ( 'U', 'X', '0', '0', '0', '0', '0', '0', 'X' ), -- | 0 | ( 'U', 'X', '0', '1', '1', '1', '1', '1', 'X' ), -- | 1 | ( 'U', 'X', '0', '1', 'Z', 'W', 'L', 'H', 'X' ), -- | Z | ( 'U', 'X', '0', '1', 'W', 'W', 'W', 'W', 'X' ), -- | W | ( 'U', 'X', '0', '1', 'L', 'W', 'L', 'W', 'X' ), -- | L | ( 'U', 'X', '0', '1', 'H', 'W', 'W', 'H', 'X' ), -- | H | ( 'U', 'X', 'X', 'X', 'X', 'X', 'X', 'X', 'X' ) -- | - | ); FUNCTION resolve ( s : std_ulogic_vector ) RETURN std_ulogic IS VARIABLE result : std_ulogic := 'Z'; -- weakest state default BEGIN -- the test for a single driver is essential otherwise the -- loop would return 'X' for a single driver of '-' and that -- would conflict with the value of a single driver unresolved -- signal. IF (s'LENGTH = 1) THEN RETURN s(s'LOW); ELSE FOR i IN s'RANGE LOOP result := resolve_table(result, s(i)); END LOOP; END IF; RETURN result; END resolve; end logic_pack;
