Source file System09_base/common.vhd

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-------------------------------------------------------------------- 
-- Company       : XESS Corp. 
-- Engineer      : Dave Vanden Bout 
-- Creation Date : 05/17/2005 
-- Copyright     : 2005, XESS Corp 
-- Tool Versions : WebPACK 6.3.03i 
-- 
-- Description: 
--    Miscellaneous VHDL constants and functions 
-- 
-- Revision: 
--    1.0.0 
-- 
-- Additional Comments: 
--    1.1.0: 
--        Added int_select() and real_select functions. 
--    1.0.0: 
--        Initial release. 
-- 
-- License: 
--    This code can be freely distributed and modified as long as 
--    this header is not removed. 
-------------------------------------------------------------------- 
 
 
 
library IEEE; 
use IEEE.std_logic_1164.all; 
use IEEE.numeric_std.all; 
 
--* @brief Miscellaneous VHDL constants and functions 
--* 
--* @author Dave Vanden Bout 
--* @version 1.1.0 from 05/17/2005 
 
package common is 
 
  constant YES                :    std_logic := '1'; 
  constant NO                 :    std_logic := '0'; 
  constant HI                 :    std_logic := '1'; 
  constant LO                 :    std_logic := '0'; 
  constant ONE                :    std_logic := '1'; 
  constant ZERO               :    std_logic := '0'; 
  -- convert a Boolean to a std_logic 
  function boolean2stdlogic(b : in boolean) return std_logic; 
  -- find the base-2 logarithm of a number 
  function log2(v             : in natural) return natural; 
  -- select one of two integers based on a Boolean 
  function int_select(s       : in boolean; a : in integer; b : in integer) return integer; 
  -- select one of two reals based on a Boolean 
  function real_select(s      : in boolean; a : in real; b : in real) return real; 
 
end package common; 
 
 
 
library IEEE; 
use IEEE.std_logic_1164.all; 
use IEEE.numeric_std.all; 
 
 
package body common is 
 
  --* convert a Boolean to a std_logic 
  function boolean2stdlogic(b : in boolean) return std_logic is 
    variable s                :    std_logic; 
  begin 
    if b then 
      s := '1'; 
    else 
      s := '0'; 
    end if; 
    return s; 
  end function boolean2stdlogic; 
 
  --* find the base 2 logarithm of a number 
  function log2(v : in natural) return natural is 
    variable n    :    natural; 
    variable logn :    natural; 
  begin 
    n      := 1; 
    for i in 0 to 128 loop 
      logn := i; 
      exit when (n >= v); 
      n    := n * 2; 
    end loop; 
    return logn; 
  end function log2; 
 
  --* select one of two integers based on a Boolean 
  function int_select(s : in boolean; a : in integer; b : in integer) return integer is 
  begin 
    if s then 
      return a; 
    else 
      return b; 
    end if; 
    return a; 
  end function int_select; 
 
  --* select one of two reals based on a Boolean 
  function real_select(s : in boolean; a : in real; b : in real) return real is 
  begin 
    if s then 
      return a; 
    else 
      return b; 
    end if; 
    return a; 
  end function real_select; 
 
end package body common;