| Line 1... |
Line 1... |
---------------------------------------------------------------------
|
--------------------------------------------------------------------------------
|
|
-- mips_shifter.vhdl -- combinational barrel shifter
|
|
--
|
|
--------------------------------------------------------------------------------
|
|
-- Copyright (C) 2010 Jose A. Ruiz
|
|
--
|
|
-- This source file may be used and distributed without
|
|
-- restriction provided that this copyright statement is not
|
|
-- removed from the file and that any derivative work contains
|
|
-- the original copyright notice and the associated disclaimer.
|
|
--
|
|
-- This source file is free software; you can redistribute it
|
|
-- and/or modify it under the terms of the GNU Lesser General
|
|
-- Public License as published by the Free Software Foundation;
|
|
-- either version 2.1 of the License, or (at your option) any
|
|
-- later version.
|
|
--
|
|
-- This source is distributed in the hope that it will be
|
|
-- useful, but WITHOUT ANY WARRANTY; without even the implied
|
|
-- warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
|
|
-- PURPOSE. See the GNU Lesser General Public License for more
|
|
-- details.
|
|
--
|
|
-- You should have received a copy of the GNU Lesser General
|
|
-- Public License along with this source; if not, download it
|
|
-- from http://www.opencores.org/lgpl.shtml
|
|
--------------------------------------------------------------------------------
|
|
|
---------------------------------------------------------------------
|
|
library ieee;
|
library ieee;
|
use ieee.std_logic_1164.all;
|
use ieee.std_logic_1164.all;
|
use ieee.std_logic_arith.all;
|
use ieee.std_logic_arith.all;
|
use ieee.std_logic_signed.all;
|
use ieee.std_logic_signed.all;
|
|
|
| Line 36... |
Line 61... |
-- we'll cut the area by 4/11 more or less (depends on how many dedicated
|
-- we'll cut the area by 4/11 more or less (depends on how many dedicated
|
-- muxes vs. LUTs the synth will use).
|
-- muxes vs. LUTs the synth will use).
|
-- The barrel shifter can account for as much as 1/4 of the CPU area
|
-- The barrel shifter can account for as much as 1/4 of the CPU area
|
-- (excluding mult/div unit) so it makes sense to be cheap here if what we
|
-- (excluding mult/div unit) so it makes sense to be cheap here if what we
|
-- want is a small core.
|
-- want is a small core.
|
|
-- NOTE: this logic may or may not be in the critical delay path of the
|
|
-- core, depending on the cache implementation. See your synthesis report.
|
|
|
-- Reverse input when shifting right
|
-- Reverse input when shifting right
|
input_reversed:
|
input_reversed:
|
for i in 0 to 31 generate
|
for i in 0 to 31 generate
|
begin
|
begin
|
