-- The Potato Processor - A simple processor for FPGAs
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-- The Potato Processor - A simple processor for FPGAs
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-- (c) Kristian Klomsten Skordal 2014 - 2015 <kristian.skordal@wafflemail.net>
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-- (c) Kristian Klomsten Skordal 2014 - 2015 <kristian.skordal@wafflemail.net>
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-- Report bugs and issues on <http://opencores.org/project,potato,bugtracker>
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-- Report bugs and issues on <http://opencores.org/project,potato,bugtracker>
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library ieee;
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library ieee;
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use ieee.std_logic_1164.all;
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use ieee.std_logic_1164.all;
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use work.pp_types.all;
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use work.pp_types.all;
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use work.pp_constants.all;
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use work.pp_constants.all;
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entity pp_alu_control_unit is
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entity pp_alu_control_unit is
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port(
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port(
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opcode : in std_logic_vector( 4 downto 0);
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opcode : in std_logic_vector( 4 downto 0);
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funct3 : in std_logic_vector( 2 downto 0);
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funct3 : in std_logic_vector( 2 downto 0);
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funct7 : in std_logic_vector( 6 downto 0);
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funct7 : in std_logic_vector( 6 downto 0);
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-- Sources of ALU operands:
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-- Sources of ALU operands:
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alu_x_src, alu_y_src : out alu_operand_source;
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alu_x_src, alu_y_src : out alu_operand_source;
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-- ALU operation:
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-- ALU operation:
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alu_op : out alu_operation
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alu_op : out alu_operation
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);
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);
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end entity pp_alu_control_unit;
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end entity pp_alu_control_unit;
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architecture behaviour of pp_alu_control_unit is
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architecture behaviour of pp_alu_control_unit is
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begin
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begin
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decode_alu: process(opcode, funct3, funct7)
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decode_alu: process(opcode, funct3, funct7)
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begin
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begin
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case opcode is
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case opcode is
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when b"01101" => -- Load upper immediate
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when b"01101" => -- Load upper immediate
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alu_x_src <= ALU_SRC_NULL;
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alu_x_src <= ALU_SRC_NULL;
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alu_y_src <= ALU_SRC_IMM;
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alu_y_src <= ALU_SRC_IMM;
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alu_op <= ALU_ADD;
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alu_op <= ALU_ADD;
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when b"00101" => -- Add upper immediate to PC
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when b"00101" => -- Add upper immediate to PC
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alu_x_src <= ALU_SRC_PC;
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alu_x_src <= ALU_SRC_PC;
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alu_y_src <= ALU_SRC_IMM;
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alu_y_src <= ALU_SRC_IMM;
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alu_op <= ALU_ADD;
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alu_op <= ALU_ADD;
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when b"11011" => -- Jump and link
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when b"11011" => -- Jump and link
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alu_x_src <= ALU_SRC_PC_NEXT;
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alu_x_src <= ALU_SRC_PC_NEXT;
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alu_y_src <= ALU_SRC_NULL;
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alu_y_src <= ALU_SRC_NULL;
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alu_op <= ALU_ADD;
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alu_op <= ALU_ADD;
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when b"11001" => -- Jump and link register
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when b"11001" => -- Jump and link register
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alu_x_src <= ALU_SRC_PC_NEXT;
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alu_x_src <= ALU_SRC_PC_NEXT;
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alu_y_src <= ALU_SRC_NULL;
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alu_y_src <= ALU_SRC_NULL;
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alu_op <= ALU_ADD;
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alu_op <= ALU_ADD;
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when b"11000" => -- Branch operations
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when b"11000" => -- Branch operations
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-- The funct3 field decides which type of branch comparison is
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-- The funct3 field decides which type of branch comparison is
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-- done; this is decoded in the branch comparator module.
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-- done; this is decoded in the branch comparator module.
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alu_x_src <= ALU_SRC_NULL;
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alu_x_src <= ALU_SRC_NULL;
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alu_y_src <= ALU_SRC_NULL;
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alu_y_src <= ALU_SRC_NULL;
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alu_op <= ALU_NOP;
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alu_op <= ALU_NOP;
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when b"00000" => -- Load instruction
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when b"00000" => -- Load instruction
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alu_x_src <= ALU_SRC_REG;
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alu_x_src <= ALU_SRC_REG;
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alu_y_src <= ALU_SRC_IMM;
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alu_y_src <= ALU_SRC_IMM;
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alu_op <= ALU_ADD;
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alu_op <= ALU_ADD;
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when b"01000" => -- Store instruction
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when b"01000" => -- Store instruction
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alu_x_src <= ALU_SRC_REG;
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alu_x_src <= ALU_SRC_REG;
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alu_y_src <= ALU_SRC_IMM;
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alu_y_src <= ALU_SRC_IMM;
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alu_op <= ALU_ADD;
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alu_op <= ALU_ADD;
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when b"00100" => -- Register-immediate operations
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when b"00100" => -- Register-immediate operations
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alu_x_src <= ALU_SRC_REG;
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alu_x_src <= ALU_SRC_REG;
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if funct3 = b"001" or funct3 = b"101" then
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if funct3 = b"001" or funct3 = b"101" then
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alu_y_src <= ALU_SRC_SHAMT;
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alu_y_src <= ALU_SRC_SHAMT;
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else
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else
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alu_y_src <= ALU_SRC_IMM;
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alu_y_src <= ALU_SRC_IMM;
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end if;
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end if;
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case funct3 is
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case funct3 is
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when b"000" =>
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when b"000" =>
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alu_op <= ALU_ADD;
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alu_op <= ALU_ADD;
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when b"001" =>
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when b"001" =>
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alu_op <= ALU_SLL;
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alu_op <= ALU_SLL;
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when b"010" =>
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when b"010" =>
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alu_op <= ALU_SLT;
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alu_op <= ALU_SLT;
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when b"011" =>
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when b"011" =>
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alu_op <= ALU_SLTU;
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alu_op <= ALU_SLTU;
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when b"100" =>
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when b"100" =>
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alu_op <= ALU_XOR;
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alu_op <= ALU_XOR;
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when b"101" =>
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when b"101" =>
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if funct7 = b"0000000" then
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if funct7 = b"0000000" then
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alu_op <= ALU_SRL;
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alu_op <= ALU_SRL;
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else
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else
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alu_op <= ALU_SRA;
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alu_op <= ALU_SRA;
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end if;
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end if;
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when b"110" =>
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when b"110" =>
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alu_op <= ALU_OR;
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alu_op <= ALU_OR;
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when b"111" =>
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when b"111" =>
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alu_op <= ALU_AND;
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alu_op <= ALU_AND;
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when others =>
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when others =>
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alu_op <= ALU_NOP;
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alu_op <= ALU_INVALID;
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end case;
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end case;
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when b"01100" => -- Register-register operations
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when b"01100" => -- Register-register operations
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alu_x_src <= ALU_SRC_REG;
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alu_x_src <= ALU_SRC_REG;
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alu_y_src <= ALU_SRC_REG;
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alu_y_src <= ALU_SRC_REG;
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case funct3 is
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case funct3 is
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when b"000" =>
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when b"000" =>
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if funct7 = b"0000000" then
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if funct7 = b"0000000" then
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alu_op <= ALU_ADD;
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alu_op <= ALU_ADD;
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else
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else
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alu_op <= ALU_SUB;
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alu_op <= ALU_SUB;
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end if;
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end if;
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when b"001" =>
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when b"001" =>
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alu_op <= ALU_SLL;
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alu_op <= ALU_SLL;
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when b"010" =>
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when b"010" =>
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alu_op <= ALU_SLT;
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alu_op <= ALU_SLT;
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when b"011" =>
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when b"011" =>
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alu_op <= ALU_SLTU;
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alu_op <= ALU_SLTU;
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when b"100" =>
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when b"100" =>
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alu_op <= ALU_XOR;
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alu_op <= ALU_XOR;
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when b"101" =>
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when b"101" =>
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if funct7 = b"0000000" then
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if funct7 = b"0000000" then
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alu_op <= ALU_SRL;
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alu_op <= ALU_SRL;
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else
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else
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alu_op <= ALU_SRA;
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alu_op <= ALU_SRA;
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end if;
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end if;
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when b"110" =>
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when b"110" =>
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alu_op <= ALU_OR;
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alu_op <= ALU_OR;
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when b"111" =>
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when b"111" =>
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alu_op <= ALU_AND;
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alu_op <= ALU_AND;
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when others =>
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when others =>
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alu_op <= ALU_NOP;
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alu_op <= ALU_INVALID;
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end case;
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end case;
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when b"00011" => -- Fence instructions, ignored
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alu_x_src <= ALU_SRC_REG;
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alu_y_src <= ALU_SRC_REG;
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alu_op <= ALU_NOP;
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when b"11100" => -- System instructions
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when b"11100" => -- System instructions
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alu_x_src <= ALU_SRC_CSR;
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alu_x_src <= ALU_SRC_CSR;
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alu_y_src <= ALU_SRC_NULL;
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alu_y_src <= ALU_SRC_NULL;
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alu_op <= ALU_ADD;
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alu_op <= ALU_ADD;
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when others =>
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when others =>
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alu_x_src <= ALU_SRC_REG;
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alu_x_src <= ALU_SRC_REG;
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alu_y_src <= ALU_SRC_REG;
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alu_y_src <= ALU_SRC_REG;
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alu_op <= ALU_NOP;
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alu_op <= ALU_INVALID;
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end case;
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end case;
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end process decode_alu;
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end process decode_alu;
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end architecture behaviour;
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end architecture behaviour;
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