---------------------------------------------------------------
-- A package with definitions of some constants and subtypes.
-- The entity mem uses the defined package. 
---------------------------------------------------------------

PACKAGE  my_package IS
   CONSTANT word_size: positive := 32;
   SUBTYPE address IS bit_vector(word_size-1 DOWNTO 0);
   SUBTYPE bus IS bit_vector(word_size-1 DOWNTO 0);
END PACKAGE my_package;

USE WORK.my_package.ALL;
ENTITY mem IS
   PORT( addr: IN address; 
         d_in : IN bus; 
         d_out : OUT bus);
END ENTITY mem;

ARCHITECTURE  sample OF mem IS
   CONSTANT pi: real := 3.14159; 
BEGIN 
   P1: PROCESS (sensitivity_list) IS 
     VARIABLE counter: integer; 
   BEGIN 
     -- statements using pi, counter, addr, d_in, d_out 
   END PROCESS P1; 
END ARCHITECTURE sample;