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-- The Potato Processor - A simple processor for FPGAs

-- (c) Kristian Klomsten Skordal 2014 <kristian.skordal@wafflemail.net>

-- Report bugs and issues on <http://opencores.org/project,potato,bugtracker>

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

use work.pp_csr.all;

--! @brief ALU used for calculating new values of control and status registers.

entity pp_csr_alu is

        port(

                x, y          : in  std_logic_vector(31 downto 0);

                result        : out std_logic_vector(31 downto 0);

                immediate     : in  std_logic_vector(4 downto 0);

                use_immediate : in  std_logic;

                write_mode    : in  csr_write_mode

        );

end entity pp_csr_alu;

architecture behaviour of pp_csr_alu is

        signal a, b : std_logic_vector(31 downto 0);

begin

        a <= x;

        b <= y when use_immediate = '0' else std_logic_vector(resize(unsigned(immediate), b'length));

        calculate: process(a, b, write_mode)

        begin

                case write_mode is

                        when CSR_WRITE_NONE =>

                                result <= a;

                        when CSR_WRITE_SET =>

                                result <= a or b;

                        when CSR_WRITE_CLEAR =>

                                result <= a and (not b);

                        when CSR_WRITE_REPLACE =>

                                result <= b;

                end case;

        end process calculate;

end architecture behaviour;