Subversion Repositories plasma_fpu

-- --------------------------------------------------------------------------

-- >>>>>>>>>>>>>>>>>>>>>>>>>>>> COPYRIGHT NOTICE <<<<<<<<<<<<<<<<<<<<<<<<<<<<

-- --------------------------------------------------------------------------

-- TITLE:       Plasma COMPARATOR

-- AUTHOR:      Alex Schoenberger (Alex.Schoenberger@ies.tu-darmstadt.de)

-- COMMENT:     This project is based on Plasma CPU core by Steve Rhoads

--

-- www.ies.tu-darmstadt.de

-- TU Darmstadt

-- Institute for Integrated Systems

-- Merckstr. 25

-- 

-- 64283 Darmstadt - GERMANY

-- --------------------------------------------------------------------------

-- PROJECT:       Plasma CPU core with FPU

-- FILENAME:      plasma_comparator.vhd

-- --------------------------------------------------------------------------

-- COPYRIGHT: 

--  This project is distributed by GPLv2.0

--  Software placed into the public domain by the author.

--  Software 'as is' without warranty.  Author liable for nothing.

-- --------------------------------------------------------------------------

-- DESCRIPTION:

--    compares input values depeding on operation code

--

--    SYNTHESIZABLE

--

----------------------------------------------------------------------------

-- Revision History

-- --------------------------------------------------------------------------

-- Revision   Date    Author     CHANGES

-- 1.0      4/2014    AS         initial

-- 2.0      5/2015    AS         works with MIPS I commands directly

-- --------------------------------------------------------------------------

library IEEE;

   use IEEE.std_logic_1164.ALL;

library PLASMA;

  use PLASMA.mips_instruction_set.ALL;

  use PLASMA.plasma_pack.ALL;

entity plasma_comparator is

    port(

      comp_a_in               : in  t_plasma_word;

      comp_b_in               : in  t_plasma_word;

      comp_func               : in  t_mips_opcode;

      comp_out                : out std_logic

    );

end entity plasma_comparator;

architecture structure_comparator of plasma_comparator is

  alias  func           : std_logic_vector(2 downto 0) is comp_func(2 downto 0);

  signal comp_eq        : std_logic;            -- input values are equal

  signal comp_eq_z      : std_logic;            -- input = 0

  signal comp_neg       : std_logic;            -- input < 0

begin

  comp_eq       <= '1' when comp_a_in = comp_b_in         else '0';

  comp_eq_z     <= '1' when comp_a_in = PLASMA_ZERO_WORD  else '0';

  comp_neg      <= comp_a_in(PLASMA_DATA_WIDTH - 1);                    -- check MSB

  -- COMPARATOR MUX

  with func select

    comp_out    <=  comp_eq                     when "100",   -- BEQ

                    not comp_eq                 when "101",   -- BNE

                    comp_neg or comp_eq_z       when "110",   -- BLEZ

                    not(comp_neg or comp_eq_z)  when "111",   -- BGTZ

                    comp_neg                    when "000",   -- BLTZ

                    not comp_neg                when "001",   -- BGEZ

                    '0'                         when others;

end architecture structure_comparator;