-- Copyright © 1993 by  McGraw-Hill, Inc. and Zainalabedin Navabi

-- FIGURE 5.4 




-- ENTITY DECLARATION OF NIBBLE-COMPARATOR TEST BENCH :

ENTITY nibble_comparator_test_bench IS
END nibble_comparator_test_bench ;
--




-- PROCEDURAL ARCHITECTURE OF NIBBLE-COMPARATOR TEST BENCH :

ARCHITECTURE procedural OF nibble_comparator_test_bench IS
  TYPE integer IS ARRAY (0 TO 12) OF INTEGER;
  PROCEDURE apply_data
    (SIGNAL target : OUT BIT_VECTOR (3 DOWNTO 0);
       CONSTANT values : IN  integers;
       CONSTANT period : IN TIME )
    IS
    VARIABLE j: INTEGER;
    VARIABLE tmp : INTEGER := O;
    VARIABLE buf : BIT_VECTOR (3 DOWNTO 0);
  BEGIN
    FOR i IN 0 TO 12 LOOP
      tmp:=values (i);
      j:=0;
      WHILE j <= 3
        IF (tmp MOD 2 = 1) THEN
          buf(j) := '1';
        ELSE buf (j) := '0';
        ENDIF;
        tmp := tmp / 2;
        j := j + 1 ;
      END LOOP
      target <= TRANSPORT buf AFTER i * period ;
    END LOOP;
  END apply_data;

  COMPONENT comp4 PORT (
    a, b : IN bit_vector (3 DOWNTO 0); gt, eq, lt : IN BIT;
    a_gt_b, a_eq_b, a_lt_b : OUT BIT);
  END COMPONENT;
  FOR a1 : comp4 USE ENTITY WORK.nibble_comparator(structural);
  SIGNAL a, b : BIT_VECTOR (3 DOWNTO 0); 
  SIGNAL eql, lss, gtr : BIT;
  SIGNAL vdd : BIT := '1';
  SIGNAL gnd : BIT := '0';
BEGIN
  a1: comp4 PORT MAP (a, b, gnd, vdd, gnd, gtr, eql, lss);
  apply_data (a, 00&15&15&14&14&14&14&10&00&15&00&00&15, 500 NS);
  apply_data (b, 00&14&14&15&15&12&12&12&15&15&15&00&00, 500 NS);
END procedural;
--