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--------------------------------------------------------------------- -- TITLE: Plasma CPU core -- AUTHOR: Steve Rhoads (rhoadss@yahoo.com) -- DATE CREATED: 2/15/01 -- FILENAME: mlite_cpu.vhd -- PROJECT: Plasma CPU core -- COPYRIGHT: Software placed into the public domain by the author. -- Software 'as is' without warranty. Author liable for nothing. -- NOTE: MIPS(tm) and MIPS I(tm) are registered trademarks of MIPS -- Technologies. MIPS Technologies does not endorse and is not -- associated with this project. -- DESCRIPTION: -- Top level VHDL document that ties the nine other entities together. -- -- Executes all MIPS I(tm) opcodes but exceptions and non-aligned -- memory accesses. 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 -- -- The CPU is implemented as a two or three stage pipeline. -- An add instruction would take the following steps (see cpu.gif): -- Stage #0: -- 1. The "pc_next" entity passes the program counter (PC) to the -- "mem_ctrl" entity which fetches the opcode from memory. -- Stage #1: -- 2. The memory returns the opcode. -- Stage #2: -- 3. "Mem_ctrl" passes the opcode to the "control" entity. -- 4. "Control" converts the 32-bit opcode to a 60-bit VLWI opcode -- and sends control signals to the other entities. -- 5. Based on the rs_index and rt_index control signals, "reg_bank" -- sends the 32-bit reg_source and reg_target to "bus_mux". -- 6. Based on the a_source and b_source control signals, "bus_mux" -- multiplexes reg_source onto a_bus and reg_target onto b_bus. -- Stage #3 (part of stage #2 if using two stage pipeline): -- 7. Based on the alu_func control signals, "alu" adds the values -- from a_bus and b_bus and places the result on c_bus. -- 8. Based on the c_source control signals, "bus_bux" multiplexes -- c_bus onto reg_dest. -- 9. Based on the rd_index control signal, "reg_bank" saves -- reg_dest into the correct register. -- Stage #3b: -- 10. Read or write memory if needed. -- -- All signals are active high. -- Here are the signals for writing a character to address 0xffff -- when using a two stage pipeline: -- -- Program: -- addr value opcode -- ============================= -- 3c: 00000000 nop -- 40: 34040041 li $a0,0x41 -- 44: 3405ffff li $a1,0xffff -- 48: a0a40000 sb $a0,0($a1) -- 4c: 00000000 nop -- 50: 00000000 nop -- -- intr_in mem_pause -- reset_in byte_we Stages -- ns address data_w data_r 40 44 48 4c 50 -- 3600 0 0 00000040 00000000 34040041 0 0 1 -- 3700 0 0 00000044 00000000 3405FFFF 0 0 2 1 -- 3800 0 0 00000048 00000000 A0A40000 0 0 2 1 -- 3900 0 0 0000004C 41414141 00000000 0 0 2 1 -- 4000 0 0 0000FFFC 41414141 XXXXXX41 1 0 3 2 -- 4100 0 0 00000050 00000000 00000000 0 0 1 --------------------------------------------------------------------- library ieee; use work.mlite_pack.all; use ieee.std_logic_1164.all; use ieee.std_logic_unsigned.all; entity mlite_cpu is generic(memory_type : string := "XILINX_16X"; --ALTERA_LPM, or DUAL_PORT_ mult_type : string := "DEFAULT"; --AREA_OPTIMIZED shifter_type : string := "DEFAULT"; --AREA_OPTIMIZED alu_type : string := "DEFAULT"; --AREA_OPTIMIZED pipeline_stages : natural := 2); --2 or 3 port(clk : in std_logic; reset_in : in std_logic; intr_in : in std_logic; address_next : out std_logic_vector(31 downto 2); --for synch ram byte_we_next : out std_logic_vector(3 downto 0); address : out std_logic_vector(31 downto 2); byte_we : out std_logic_vector(3 downto 0); data_w : out std_logic_vector(31 downto 0); data_r : in std_logic_vector(31 downto 0); mem_pause : in std_logic); end; --entity mlite_cpu architecture logic of mlite_cpu is --When using a two stage pipeline "sigD <= sig". --When using a three stage pipeline "sigD <= sig when rising_edge(clk)", -- so sigD is delayed by one clock cycle. signal opcode : std_logic_vector(31 downto 0); signal rs_index : std_logic_vector(5 downto 0); signal rt_index : std_logic_vector(5 downto 0); signal rd_index : std_logic_vector(5 downto 0); signal rd_indexD : std_logic_vector(5 downto 0); signal reg_source : std_logic_vector(31 downto 0); signal reg_target : std_logic_vector(31 downto 0); signal reg_dest : std_logic_vector(31 downto 0); signal reg_destD : std_logic_vector(31 downto 0); signal a_bus : std_logic_vector(31 downto 0); signal a_busD : std_logic_vector(31 downto 0); signal b_bus : std_logic_vector(31 downto 0); signal b_busD : std_logic_vector(31 downto 0); signal c_bus : std_logic_vector(31 downto 0); signal c_alu : std_logic_vector(31 downto 0); signal c_shift : std_logic_vector(31 downto 0); signal c_mult : std_logic_vector(31 downto 0); signal c_memory : std_logic_vector(31 downto 0); signal imm : std_logic_vector(15 downto 0); signal pc_future : std_logic_vector(31 downto 2); signal pc_current : std_logic_vector(31 downto 2); signal pc_plus4 : std_logic_vector(31 downto 2); signal alu_func : alu_function_type; signal alu_funcD : alu_function_type; signal shift_func : shift_function_type; signal shift_funcD : shift_function_type; signal mult_func : mult_function_type; signal mult_funcD : mult_function_type; signal branch_func : 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_ctrl : std_logic; signal pause_pipeline : std_logic; signal pause_any : std_logic; signal pause_non_ctrl : std_logic; signal pause_bank : std_logic; signal nullify_op : std_logic; signal intr_enable : std_logic; signal intr_signal : std_logic; signal exception_sig : std_logic; signal reset_reg : std_logic_vector(3 downto 0); signal reset : std_logic; begin --architecture pause_any <= (mem_pause or pause_ctrl) or (pause_mult or pause_pipeline); pause_non_ctrl <= (mem_pause or pause_mult) or pause_pipeline; pause_bank <= (mem_pause or pause_ctrl or pause_mult) and not pause_pipeline; nullify_op <= '1' when (pc_source = FROM_LBRANCH and take_branch = '0') or intr_signal = '1' or exception_sig = '1' else '0'; c_bus <= c_alu or c_shift or c_mult; reset <= '1' when reset_in = '1' or reset_reg /= "1111" else '0'; --synchronize reset and interrupt pins intr_proc: process(clk, reset_in, reset_reg, intr_in, intr_enable, pc_source, pc_current, pause_any) begin if reset_in = '1' then reset_reg <= "0000"; intr_signal <= '0'; elsif rising_edge(clk) then if reset_reg /= "1111" then reset_reg <= reset_reg + 1; end if; --don't try to interrupt a multi-cycle instruction if pause_any = '0' then if intr_in = '1' and intr_enable = '1' and pc_source = FROM_INC4 then --the epc will contain pc+4 intr_signal <= '1'; else intr_signal <= '0'; end if; end if; end if; end process; u1_pc_next: pc_next PORT MAP ( clk => clk, reset_in => reset, take_branch => take_branch, pause_in => pause_any, pc_new => c_bus(31 downto 2), opcode25_0 => opcode(25 downto 0), pc_source => pc_source, pc_future => pc_future, pc_current => pc_current, pc_plus4 => pc_plus4); u2_mem_ctrl: mem_ctrl PORT MAP ( clk => clk, reset_in => reset, pause_in => pause_non_ctrl, nullify_op => nullify_op, address_pc => pc_future, opcode_out => opcode, address_in => c_bus, mem_source => mem_source, data_write => reg_target, data_read => c_memory, pause_out => pause_ctrl, address_next => address_next, byte_we_next => byte_we_next, address => address, byte_we => byte_we, data_w => data_w, data_r => data_r); u3_control: 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_func, shift_func => shift_func, mult_func => mult_func, branch_func => branch_func, 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, exception_out=> exception_sig); u4_reg_bank: reg_bank generic map(memory_type => memory_type) port map ( clk => clk, reset_in => reset, pause => pause_bank, rs_index => rs_index, rt_index => rt_index, rd_index => rd_indexD, reg_source_out => reg_source, reg_target_out => reg_target, reg_dest_new => reg_destD, intr_enable => intr_enable); u5_bus_mux: 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_current, c_pc_plus4 => pc_plus4, c_mux => c_source, reg_dest_out => reg_dest, branch_func => branch_func, take_branch => take_branch); u6_alu: alu generic map (alu_type => alu_type) port map ( a_in => a_busD, b_in => b_busD, alu_function => alu_funcD, c_alu => c_alu); u7_shifter: shifter generic map (shifter_type => shifter_type) port map ( value => b_busD, shift_amount => a_busD(4 downto 0), shift_func => shift_funcD, c_shift => c_shift); u8_mult: mult generic map (mult_type => mult_type) port map ( clk => clk, reset_in => reset, a => a_busD, b => b_busD, mult_func => mult_funcD, c_mult => c_mult, pause_out => pause_mult); pipeline2: if pipeline_stages <= 2 generate a_busD <= a_bus; b_busD <= b_bus; alu_funcD <= alu_func; shift_funcD <= shift_func; mult_funcD <= mult_func; rd_indexD <= rd_index; reg_destD <= reg_dest; pause_pipeline <= '0'; end generate; --pipeline2 pipeline3: if pipeline_stages > 2 generate --When operating in three stage pipeline mode, the following signals --are delayed by one clock cycle: a_bus, b_bus, alu/shift/mult_func, --c_source, and rd_index. u9_pipeline: pipeline port map ( clk => clk, reset => reset, a_bus => a_bus, a_busD => a_busD, b_bus => b_bus, b_busD => b_busD, alu_func => alu_func, alu_funcD => alu_funcD, shift_func => shift_func, shift_funcD => shift_funcD, mult_func => mult_func, mult_funcD => mult_funcD, reg_dest => reg_dest, reg_destD => reg_destD, rd_index => rd_index, rd_indexD => rd_indexD, rs_index => rs_index, rt_index => rt_index, pc_source => pc_source, mem_source => mem_source, a_source => a_source, b_source => b_source, c_source => c_source, c_bus => c_bus, pause_any => pause_any, pause_pipeline => pause_pipeline); end generate; --pipeline3 end; --architecture logic
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