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entity Alu is
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entity Alu is
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generic (n : integer := nBits - 1); --! Generic value (Used to easily change the size of the Alu on the package)
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generic (n : integer := nBits - 1); --! Generic value (Used to easily change the size of the Alu on the package)
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Port ( A : in STD_LOGIC_VECTOR (n downto 0); --! Alu Operand 1
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Port ( A : in STD_LOGIC_VECTOR (n downto 0); --! Alu Operand 1
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B : in STD_LOGIC_VECTOR (n downto 0); --! Alu Operand 2
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B : in STD_LOGIC_VECTOR (n downto 0); --! Alu Operand 2
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S : out STD_LOGIC_VECTOR (n downto 0); --! Alu Output
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S : out STD_LOGIC_VECTOR (n downto 0); --! Alu Output
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flagsOut : out STD_LOGIC_VECTOR(2 downto 0); --! Flags from current operation
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sel : in aluOps); --! Select operation
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sel : in aluOps); --! Select operation
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end Alu;
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end Alu;
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--! @brief Arithmetic logic unit, refer to this page for more information http://en.wikipedia.org/wiki/Arithmetic_logic_unit
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--! @brief Arithmetic logic unit, refer to this page for more information http://en.wikipedia.org/wiki/Arithmetic_logic_unit
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--! @details This circuit will be excited by the control unit to perfom some arithimetic, or logic operation (Depending on the opcode selected)
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--! @details This circuit will be excited by the control unit to perfom some arithimetic, or logic operation (Depending on the opcode selected)
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begin
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begin
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--! Behavior description of combinational circuit (Can not infer any FF(Flip flop)) of the Alu
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--! Behavior description of combinational circuit (Can not infer any FF(Flip flop)) of the Alu
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process (A,B,sel) is
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process (A,B,sel) is
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variable mulResult : std_logic_vector(((nBits*2) - 1)downto 0);
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variable mulResult : std_logic_vector(((nBits*2) - 1)downto 0);
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variable FLAG_CARRY, FLAG_ZERO , FLAG_SIGN : STD_LOGIC;
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variable intermediate_S : STD_LOGIC_VECTOR(nBits downto 0); -- One more bit to detect overflows...
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begin
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begin
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case sel is
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case sel is
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when alu_pass =>
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when alu_pass =>
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--Pass operation
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--Pass operation
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S <= A;
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intermediate_S := '0' & A;
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when alu_passB =>
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when alu_passB =>
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--Pass operation
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--Pass operation
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S <= B;
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intermediate_S := '0' & B;
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when alu_sum =>
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when alu_sum =>
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--Sum operation
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--Sum operation
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S <= A + B;
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intermediate_S := ('0' & A) + ('0' & B);
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when alu_sub =>
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when alu_sub =>
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--Subtraction operation
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--Subtraction operation
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S <= A - B;
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intermediate_S := ('0' & A) - ('0' & B);
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when alu_inc =>
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when alu_inc =>
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--Increment operation
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--Increment operation
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S <= A + conv_std_logic_vector(1, n+1);
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intermediate_S := ('0' & A) + conv_std_logic_vector(1, nBits);
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when alu_dec =>
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when alu_dec =>
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--Decrement operation
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--Decrement operation
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S <= A - conv_std_logic_vector(1, n+1);
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intermediate_S := ('0' & A) - conv_std_logic_vector(1, nBits);
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when alu_mul =>
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when alu_mul =>
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--Multiplication operation
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--Multiplication operation
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mulResult := A * B;
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mulResult := A * B;
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S <= mulResult((nBits - 1) downto 0);
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intermediate_S := mulResult(nBits downto 0);
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when alu_and =>
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when alu_and =>
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--And operation
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--And operation
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S <= A and B;
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intermediate_S := '0' & (A and B);
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when alu_or =>
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when alu_or =>
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--Or operation
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--Or operation
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S <= A or B;
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intermediate_S := '0' & (A or B);
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when alu_xor =>
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when alu_xor =>
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--Xor operation
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--Xor operation
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S <= A xor B;
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intermediate_S := '0' & (A xor B);
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when alu_not =>
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when alu_not =>
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--Not operation
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--Not operation
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S <= not A;
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intermediate_S := not ('0' & A);
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when alu_shfLt =>
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-- Shift left operand A (Get current value bring to left and add a zero to the right)
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intermediate_S := '0' & (A((A'HIGH - 1) downto 0) & '0'); -- "&" is the concatenate operator
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when alu_shfRt =>
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-- Shift right operand A (Add a zero to the left and copy the current value to the right)
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intermediate_S := '0' & ('0' & A(A'HIGH downto 1)); -- "&" is the concatenate operator
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when alu_roRt =>
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-- Rotate right operand A (Get the lowest bit of A, and concatenate with the others bits, taking out the latest one...)
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intermediate_S := '0' & (A(A'LOW) & A(A'HIGH downto 1)); -- If A is (7 downto 0) A'LOW is 0, and A'HIGH is 7
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when alu_roLt =>
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-- Rotate left operand A (Get the the bits from the second highest and concatenate in the end with the highest one...)
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intermediate_S := '0' & (A((A'HIGH - 1) downto 0) & A(A'HIGH));
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when others =>
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when others =>
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S <= (others => 'Z');
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intermediate_S := (others => 'Z');
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end case;
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end case;
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-- Get flags
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if (intermediate_S = 0) then
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FLAG_ZERO := '1';
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else
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FLAG_ZERO := '0';
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end if;
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FLAG_SIGN := intermediate_S(intermediate_S'HIGH - 1);
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FLAG_CARRY := intermediate_S(intermediate_S'HIGH);
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-- Pass output
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S <= intermediate_S(S'RANGE); -- S'RANGE == S(31 downto 0);
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flagsOut <= FLAG_SIGN & FLAG_ZERO & FLAG_CARRY;
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end process;
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end process;
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end Behavioral;
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end Behavioral;
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