example8-7.vhd

vhdl 实例 通过实例学习vhdl 编程

LIBRARY IEEE;
USE IEEE.Std_Logic_1164.ALL;
PACKAGE pak IS
  TYPE time_mode IS (minimum, typical, maximum);
  TYPE rise_fall IS
    RECORD
      rise : TIME;
      fall : TIME;
    END RECORD;
  TYPE time_rec IS ARRAY (minimum TO maximum) OF rise_fall;
  FUNCTION calculate (nextstate : IN Std_Logic; mode : IN time_mode;
                      delaytab : IN time_rec) RETURN TIME;
END pak;
PACKAGE BODY pak IS
  FUNCTION calculate (nextstate : IN Std_Logic; mode : IN time_mode;
                     delaytab : IN time_rec) RETURN TIME IS
  BEGIN
  CASE nextstate IS
    WHEN '0' =>
      RETURN delaytab (mode).fall;
    WHEN '1' =>
      RETURN delaytab (mode).rise;
    WHEN OTHERS =>
      IF (delaytab (mode).rise <= delaytab (mode).fall) THEN
      RETURN delaytab (mode).rise;
    ELSE
      RETURN delaytab (mode).fall;
    END IF;
  END CASE;
  END calculate;
END pak;