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[/] [opencpu32/] [trunk/] [hdl/] [opencpu32/] [Alu.vhd] - Rev 24
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--! @file --! @brief Arithmetic logic unit http://en.wikipedia.org/wiki/Arithmetic_logic_unit --! Use standard library and import the packages (std_logic_1164,std_logic_unsigned,std_logic_arith) library IEEE; use ieee.std_logic_1164.all; use ieee.std_logic_unsigned.all; use ieee.std_logic_arith.all; --! Use CPU Definitions package use work.pkgOpenCPU32.all; --! ALU is a digital circuit that performs arithmetic and logical operations. --! ALU is a digital circuit that performs arithmetic and logical operations. It's the fundamental part of the CPU entity Alu is generic (n : integer := nBits - 1); --! Generic value (Used to easily change the size of the Alu on the package) Port ( A : in STD_LOGIC_VECTOR (n downto 0); --! Alu Operand 1 B : in STD_LOGIC_VECTOR (n downto 0); --! Alu Operand 2 S : out STD_LOGIC_VECTOR (n downto 0); --! Alu Output sel : in aluOps); --! Select operation end Alu; --! @brief Arithmetic logic unit, refer to this page for more information http://en.wikipedia.org/wiki/Arithmetic_logic_unit --! @details This circuit will be excited by the control unit to perfom some arithimetic, or logic operation (Depending on the opcode selected) --! \n You can see some samples on the Internet: http://www.vlsibank.com/sessionspage.asp?titl_id=12222 architecture Behavioral of Alu is begin --! Behavior description of combinational circuit (Can not infer any FF(Flip flop)) of the Alu process (A,B,sel) is variable mulResult : std_logic_vector(((nBits*2) - 1)downto 0); begin case sel is when alu_pass => --Pass operation S <= A; when alu_passB => --Pass operation S <= B; when alu_sum => --Sum operation S <= A + B; when alu_sub => --Subtraction operation S <= A - B; when alu_inc => --Increment operation S <= A + conv_std_logic_vector(1, n+1); when alu_dec => --Decrement operation S <= A - conv_std_logic_vector(1, n+1); when alu_mul => --Multiplication operation mulResult := A * B; S <= mulResult((nBits - 1) downto 0); when alu_and => --And operation S <= A and B; when alu_or => --Or operation S <= A or B; when alu_xor => --Xor operation S <= A xor B; when alu_not => --Not operation S <= not A; when others => S <= (others => 'Z'); end case; end process; end Behavioral;
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