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--------------------------------------------------------------------- -- TITLE: MIPS CPU core -- AUTHOR: Steve Rhoads (rhoadss@yahoo.com) -- DATE CREATED: 2/15/01 -- FILENAME: mips_cpu.vhd -- PROJECT: MIPS CPU core -- COPYRIGHT: Software placed into the public domain by the author. -- Software 'as is' without warranty. Author liable for nothing. -- DESCRIPTION: -- Top level VHDL document that ties the eight other entities together. -- Implements a MIPS CPU. Based on information found in: -- "MIPS RISC Architecture" by Gerry Kane and Joe Heinrich -- and "The Designer's Guide to VHDL" by Peter J. Ashenden -- An add instruction would take the following steps (see cpu.gif): -- 1. The "pc_next" entity would have previously passed the program -- counter (PC) to the "mem_ctrl" entity. -- 2. "Mem_ctrl" passes the opcode to the "control" entity. -- 3. "Control" converts the 32-bit opcode to a 60-bit VLWI opcode -- and sends control signals to the other entities. -- 4. Based on the rs_index and rt_index control signals, "reg_bank" -- sends the 32-bit reg_source and reg_target to "bus_mux". -- 5. Based on the a_source and b_source control signals, "bus_mux" -- multiplexes reg_source onto a_bus and reg_target onto b_bus. -- 6. Based on the alu_func control signals, "alu" adds the values -- from a_bus and b_bus and places the result on c_bus. -- 7. Based on the c_source control signals, "bus_bux" multiplexes -- c_bus onto reg_dest. -- 8. Based on the rd_index control signal, "reg_bank" saves -- reg_dest into the correct register. -- The CPU is implemented as a two stage pipeline with step #1 in the -- first stage and steps #2-8 occuring the second stage. -- -- The CPU core was synthesized for 0.13 um line widths with an area -- of 0.2 millimeters squared. The maximum latency was less than 6 ns -- for a maximum clock speed of 150 MHz. --------------------------------------------------------------------- library ieee; use ieee.std_logic_1164.all; use work.mips_pack.all; entity mips_cpu is port(clk : in std_logic; reset_in : in std_logic; intr_in : in std_logic; mem_address : out std_logic_vector(31 downto 0); mem_data_w : out std_logic_vector(31 downto 0); mem_data_r : in std_logic_vector(31 downto 0); mem_sel : out std_logic_vector(3 downto 0); mem_write : out std_logic; mem_pause : in std_logic; t_pc : out std_logic_vector(31 downto 0); t_opcode : out std_logic_vector(31 downto 0); t_r_dest : out std_logic_vector(31 downto 0) ); end; --entity mips_cpu architecture logic of mips_cpu is component pc_next port(clk : in std_logic; reset_in : in std_logic; pc_new : in std_logic_vector(31 downto 2); take_branch : in std_logic; pause_in : in std_logic; opcode25_0 : in std_logic_vector(25 downto 0); pc_source : in pc_source_type; pc_out : out std_logic_vector(31 downto 0)); end component; component mem_ctrl port(clk : in std_logic; reset_in : in std_logic; pause_in : in std_logic; nullify_op : in std_logic; address_pc : in std_logic_vector(31 downto 0); opcode_out : out std_logic_vector(31 downto 0); address_data : in std_logic_vector(31 downto 0); mem_source : in mem_source_type; data_write : in std_logic_vector(31 downto 0); data_read : out std_logic_vector(31 downto 0); pause_out : out std_logic; mem_address : out std_logic_vector(31 downto 0); mem_data_w : out std_logic_vector(31 downto 0); mem_data_r : in std_logic_vector(31 downto 0); mem_byte_sel : out std_logic_vector(3 downto 0); mem_write : out std_logic; mem_pause : in std_logic); end component; component control port(opcode : in std_logic_vector(31 downto 0); intr_signal : in std_logic; rs_index : out std_logic_vector(5 downto 0); rt_index : out std_logic_vector(5 downto 0); rd_index : out std_logic_vector(5 downto 0); imm_out : out std_logic_vector(15 downto 0); alu_func : out alu_function_type; shift_func : out shift_function_type; mult_func : out mult_function_type; branch_func : out branch_function_type; a_source_out : out a_source_type; b_source_out : out b_source_type; c_source_out : out c_source_type; pc_source_out: out pc_source_type; mem_source_out:out mem_source_type); end component; component reg_bank port(clk : in std_logic; rs_index : in std_logic_vector(5 downto 0); rt_index : in std_logic_vector(5 downto 0); rd_index : in std_logic_vector(5 downto 0); reg_source_out : out std_logic_vector(31 downto 0); reg_target_out : out std_logic_vector(31 downto 0); reg_dest_new : in std_logic_vector(31 downto 0); intr_enable : out std_logic); end component; component bus_mux port(imm_in : in std_logic_vector(15 downto 0); reg_source : in std_logic_vector(31 downto 0); a_mux : in a_source_type; a_out : out std_logic_vector(31 downto 0); reg_target : in std_logic_vector(31 downto 0); b_mux : in b_source_type; b_out : out std_logic_vector(31 downto 0); c_bus : in std_logic_vector(31 downto 0); c_memory : in std_logic_vector(31 downto 0); c_pc : in std_logic_vector(31 downto 0); c_mux : in c_source_type; reg_dest_out : out std_logic_vector(31 downto 0); branch_func : in branch_function_type; take_branch : out std_logic); end component; component alu port(a_in : in std_logic_vector(31 downto 0); b_in : in std_logic_vector(31 downto 0); alu_function : in alu_function_type; c_alu : out std_logic_vector(31 downto 0)); end component; component shifter port(value : in std_logic_vector(31 downto 0); shift_amount : in std_logic_vector(4 downto 0); shift_func : in shift_function_type; c_shift : out std_logic_vector(31 downto 0)); end component; component mult port(clk : in std_logic; a, b : in std_logic_vector(31 downto 0); mult_func : in mult_function_type; c_mult : out std_logic_vector(31 downto 0); pause_out : out std_logic); end component; signal opcode : std_logic_vector(31 downto 0); signal rs_index, rt_index, rd_index : std_logic_vector(5 downto 0); signal reg_source, reg_target, reg_dest : std_logic_vector(31 downto 0); signal a_bus, b_bus, c_bus : std_logic_vector(31 downto 0); signal c_alu, c_shift, c_mult, c_memory : std_logic_vector(31 downto 0); signal imm : std_logic_vector(15 downto 0); signal pc : std_logic_vector(31 downto 0); signal alu_function : alu_function_type; signal shift_function : shift_function_type; signal mult_function : mult_function_type; signal branch_function: branch_function_type; signal take_branch : std_logic; signal a_source : a_source_type; signal b_source : b_source_type; signal c_source : c_source_type; signal pc_source : pc_source_type; signal mem_source : mem_source_type; signal pause_mult : std_logic; signal pause_memory : std_logic; signal pause : std_logic; signal nullify_op : std_logic; signal intr_enable : std_logic; signal intr_signal : std_logic; -- signal mem_byte_sel : std_logic_vector(3 downto 0); -- signal mem_write : std_logic; begin --architecture pause <= pause_mult or pause_memory; --nulify_op = pc_source==from_lbranch && take_branch=='0' nullify_op <= pc_source(1) and pc_source(0) and not take_branch; c_bus <= c_alu or c_shift or c_mult; intr_signal <= (intr_in and intr_enable) and (not pc_source(0) and not pc_source(1)); --from_inc4 u1: pc_next PORT MAP ( clk => clk, reset_in => reset_in, take_branch => take_branch, pause_in => pause, pc_new => c_alu(31 downto 2), opcode25_0 => opcode(25 downto 0), pc_source => pc_source, pc_out => pc); u2: mem_ctrl PORT MAP ( clk => clk, reset_in => reset_in, pause_in => pause, nullify_op => nullify_op, address_pc => pc, opcode_out => opcode, address_data => c_alu, mem_source => mem_source, data_write => reg_target, data_read => c_memory, pause_out => pause_memory, mem_address => mem_address, mem_data_w => mem_data_w, mem_data_r => mem_data_r, mem_byte_sel => mem_sel, mem_write => mem_write, mem_pause => mem_pause); u3: control PORT MAP ( opcode => opcode, intr_signal => intr_signal, rs_index => rs_index, rt_index => rt_index, rd_index => rd_index, imm_out => imm, alu_func => alu_function, shift_func => shift_function, mult_func => mult_function, branch_func => branch_function, a_source_out => a_source, b_source_out => b_source, c_source_out => c_source, pc_source_out=> pc_source, mem_source_out=> mem_source); u4: reg_bank port map ( clk => clk, rs_index => rs_index, rt_index => rt_index, rd_index => rd_index, reg_source_out => reg_source, reg_target_out => reg_target, reg_dest_new => reg_dest, intr_enable => intr_enable); u5: bus_mux port map ( imm_in => imm, reg_source => reg_source, a_mux => a_source, a_out => a_bus, reg_target => reg_target, b_mux => b_source, b_out => b_bus, c_bus => c_bus, c_memory => c_memory, c_pc => pc, c_mux => c_source, reg_dest_out => reg_dest, branch_func => branch_function, take_branch => take_branch); u6: alu port map ( a_in => a_bus, b_in => b_bus, alu_function => alu_function, c_alu => c_alu); u7: shifter port map ( value => b_bus, shift_amount => a_bus(4 downto 0), shift_func => shift_function, c_shift => c_shift); u8: mult port map ( clk => clk, a => a_bus, b => b_bus, mult_func => mult_function, c_mult => c_mult, pause_out => pause_mult); t_pc <= pc; t_opcode <= opcode; t_r_dest <= reg_dest; end; --architecture logic
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