Subversion Repositories potato

-- The Potato Processor - A simple processor for FPGAs

-- (c) Kristian Klomsten Skordal 2014 - 2015 <kristian.skordal@wafflemail.net>

-- Report bugs and issues on <https://github.com/skordal/potato/issues>

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

use work.pp_types.all;

use work.pp_csr.all;

use work.pp_utilities.all;

entity pp_execute is

        port(

                clk    : in std_logic;

                reset  : in std_logic;

                stall, flush : in std_logic;

                -- IRQ input:

                irq : in std_logic_vector(7 downto 0);

                -- Data memory outputs:

                dmem_address   : out std_logic_vector(31 downto 0);

                dmem_data_out  : out std_logic_vector(31 downto 0);

                dmem_data_size : out std_logic_vector( 1 downto 0);

                dmem_read_req  : out std_logic;

                dmem_write_req : out std_logic;

                -- Register addresses:

                rs1_addr_in, rs2_addr_in, rd_addr_in : in  register_address;

                rd_addr_out                          : out register_address;

                -- Register values:

                rs1_data_in, rs2_data_in : in std_logic_vector(31 downto 0);

                rd_data_out              : out std_logic_vector(31 downto 0);

                -- Constant values:

                shamt_in     : in std_logic_vector(4 downto 0);

                immediate_in : in std_logic_vector(31 downto 0);

                -- Instruction address:

                pc_in     : in  std_logic_vector(31 downto 0);

                pc_out    : out std_logic_vector(31 downto 0);

                -- Funct3 value from the instruction, used to choose which comparison

                -- is used when branching:

                funct3_in : in std_logic_vector(2 downto 0);

                -- CSR signals:

                csr_addr_in          : in  csr_address;

                csr_addr_out         : out csr_address;

                csr_write_in         : in  csr_write_mode;

                csr_write_out        : out csr_write_mode;

                csr_value_in         : in  std_logic_vector(31 downto 0);

                csr_value_out        : out std_logic_vector(31 downto 0);

                csr_writeable_in     : in  boolean;

                csr_use_immediate_in : in  std_logic;

                -- Control signals:

                alu_op_in    : in  alu_operation;

                alu_x_src_in : in  alu_operand_source;

                alu_y_src_in : in  alu_operand_source;

                rd_write_in  : in  std_logic;

                rd_write_out : out std_logic;

                branch_in    : in  branch_type;

                branch_out   : out branch_type;

                -- Memory control signals:

                mem_op_in    : in  memory_operation_type;

                mem_op_out   : out memory_operation_type;

                mem_size_in  : in  memory_operation_size;

                mem_size_out : out memory_operation_size;

                -- Whether the instruction should be counted:

                count_instruction_in  : in  std_logic;

                count_instruction_out : out std_logic;

                -- Exception control registers:

                status_in : in  csr_status_register;

                evec_in   : in  std_logic_vector(31 downto 0);

                evec_out  : out std_logic_vector(31 downto 0);

                -- Exception signals:

                decode_exception_in       : in std_logic;

                decode_exception_cause_in : in csr_exception_cause;

                -- Exception outputs:

                exception_out         : out std_logic;

                exception_context_out : out csr_exception_context;

                -- Control outputs:

                jump_out        : out std_logic;

                jump_target_out : out std_logic_vector(31 downto 0);

                -- Inputs to the forwarding logic from the MEM stage:

                mem_rd_write          : in std_logic;

                mem_rd_addr           : in register_address;

                mem_rd_value          : in std_logic_vector(31 downto 0);

                mem_csr_addr          : in csr_address;

                mem_csr_write         : in csr_write_mode;

                mem_csr_value         : in std_logic_vector(31 downto 0);

                mem_exception         : in std_logic;

                mem_exception_context : in csr_exception_context;

                -- Inputs to the forwarding logic from the WB stage:

                wb_rd_write          : in std_logic;

                wb_rd_addr           : in register_address;

                wb_rd_value          : in std_logic_vector(31 downto 0);

                wb_csr_addr          : in csr_address;

                wb_csr_write         : in csr_write_mode;

                wb_csr_value         : in std_logic_vector(31 downto 0);

                wb_exception         : in std_logic;

                wb_exception_context : in csr_exception_context;

                -- Hazard detection unit signals:

                mem_mem_op : in memory_operation_type;

                hazard_detected : out std_logic

        );

end entity pp_execute;

architecture behaviour of pp_execute is

        signal alu_op : alu_operation;

        signal alu_x_src, alu_y_src : alu_operand_source;

        signal alu_x, alu_y, alu_result : std_logic_vector(31 downto 0);

        signal rs1_addr, rs2_addr : register_address;

        signal rs1_data, rs2_data : std_logic_vector(31 downto 0);

        signal mem_op : memory_operation_type;

        signal mem_size : memory_operation_size;

        signal pc        : std_logic_vector(31 downto 0);

        signal immediate : std_logic_vector(31 downto 0);

        signal shamt     : std_logic_vector( 4 downto 0);

        signal funct3    : std_logic_vector( 2 downto 0);

        signal rs1_forwarded, rs2_forwarded : std_logic_vector(31 downto 0);

        signal branch : branch_type;

        signal branch_condition : std_logic;

        signal jump_target : std_logic_vector(31 downto 0);

        signal sr : csr_status_register;

        signal evec, evec_forwarded : std_logic_vector(31 downto 0);

        signal csr_write : csr_write_mode;

        signal csr_addr  : csr_address;

        signal csr_use_immediate : std_logic;

        signal csr_writeable : boolean;

        signal csr_value, csr_value_forwarded : std_logic_vector(31 downto 0);

        signal decode_exception : std_logic;

        signal decode_exception_cause : csr_exception_cause;

        signal exception_taken : std_logic;

        signal exception_cause : csr_exception_cause;

        signal exception_vaddr : std_logic_vector(31 downto 0);

        signal exception_context_forwarded : csr_exception_context;

        signal data_misaligned, instr_misaligned : std_logic;

        signal irq_asserted : std_logic;

        signal irq_asserted_num : std_logic_vector(3 downto 0);

begin

        -- Register values should not be latched in by a clocked process,

        -- this is already done in the register files.

        csr_value <= csr_value_in;

        rd_data_out <= alu_result;

        branch_out <= branch;

        mem_op_out <= mem_op;

        mem_size_out <= mem_size;

        csr_write_out <= csr_write;

        csr_addr_out  <= csr_addr;

        pc_out <= pc;

        exception_out <= exception_taken;

        exception_context_out <= (

                                status => exception_context_forwarded.status,

                                cause => exception_cause,

                                badvaddr => exception_vaddr

                        ) when exception_taken = '1' else exception_context_forwarded;

        jump_out <= to_std_logic(branch = BRANCH_JUMP or branch = BRANCH_JUMP_INDIRECT)

                or (to_std_logic(branch = BRANCH_CONDITIONAL) and branch_condition)

                or to_std_logic(branch = BRANCH_SRET);

        jump_target_out <= jump_target;

        evec_out <= evec_forwarded;

        exception_taken <= decode_exception or to_std_logic(exception_cause /= CSR_CAUSE_NONE) or irq_asserted;

        irq_asserted <= to_std_logic(exception_context_forwarded.status.ei = '1' and

                (irq and exception_context_forwarded.status.im) /= x"00");

        rs1_data <= rs1_data_in;

        rs2_data <= rs2_data_in;

        dmem_address <= alu_result;

        dmem_data_out <= rs2_forwarded;

        dmem_write_req <= '1' when mem_op = MEMOP_TYPE_STORE else '0';

        dmem_read_req <= '1' when memop_is_load(mem_op) else '0';

        pipeline_register: process(clk)

        begin

                if rising_edge(clk) then

                        if reset = '1' or flush = '1' then

                                rd_write_out <= '0';

                                branch <= BRANCH_NONE;

                                csr_write <= CSR_WRITE_NONE;

                                mem_op <= MEMOP_TYPE_NONE;

                                decode_exception <= '0';

                                count_instruction_out <= '0';

                        elsif stall = '0' then

                                pc <= pc_in;

                                count_instruction_out <= count_instruction_in;

                                -- Register signals:

                                rd_write_out <= rd_write_in;

                                rd_addr_out <= rd_addr_in;

                                rs1_addr <= rs1_addr_in;

                                rs2_addr <= rs2_addr_in;

                                -- ALU signals:

                                alu_op <= alu_op_in;

                                alu_x_src <= alu_x_src_in;

                                alu_y_src <= alu_y_src_in;

                                -- Control signals:

                                branch <= branch_in;

                                mem_op <= mem_op_in;

                                mem_size <= mem_size_in;

                                -- Constant values:

                                immediate <= immediate_in;

                                shamt <= shamt_in;

                                funct3 <= funct3_in;

                                -- CSR signals:

                                csr_write <= csr_write_in;

                                csr_addr <= csr_addr_in;

                                csr_use_immediate <= csr_use_immediate_in;

                                csr_writeable <= csr_writeable_in;

                                -- Status register;

                                sr <= status_in;

                                -- Exception vector base:

                                evec <= evec_in;

                                -- Instruction decoder exceptions:

                                decode_exception <= decode_exception_in;

                                decode_exception_cause <= decode_exception_cause_in;

                        end if;

                end if;

        end process pipeline_register;

        set_data_size: process(mem_size)

        begin

                case mem_size is

                        when MEMOP_SIZE_BYTE =>

                                dmem_data_size <= b"01";

                        when MEMOP_SIZE_HALFWORD =>

                                dmem_data_size <= b"10";

                        when MEMOP_SIZE_WORD =>

                                dmem_data_size <= b"00";

                        when others =>

                                dmem_data_size <= b"11";

                end case;

        end process set_data_size;

        get_irq_num: process(irq, exception_context_forwarded)

                variable temp : std_logic_vector(3 downto 0);

        begin

                temp := (others => '0');

                for i in 0 to 7 loop

                        if irq(i) = '1' and exception_context_forwarded.status.im(i) = '1' then

                                temp := std_logic_vector(to_unsigned(i, temp'length));

                                exit;

                        end if;

                end loop;

                irq_asserted_num <= temp;

        end process get_irq_num;

        data_misalign_check: process(mem_size, alu_result)

        begin

                case mem_size is

                        when MEMOP_SIZE_HALFWORD =>

                                if alu_result(0) /= '0' then

                                        data_misaligned <= '1';

                                else

                                        data_misaligned <= '0';

                                end if;

                        when MEMOP_SIZE_WORD =>

                                if alu_result(1 downto 0) /= b"00" then

                                        data_misaligned <= '1';

                                else

                                        data_misaligned <= '0';

                                end if;

                        when others =>

                                data_misaligned <= '0';

                end case;

        end process data_misalign_check;

        instr_misalign_check: instr_misaligned <= '1' when jump_target(1 downto 0) /= b"00" else '0';

        find_exception_cause: process(decode_exception, decode_exception_cause, mem_op,

                data_misaligned, instr_misaligned, irq_asserted, irq_asserted_num)

        begin

                if irq_asserted = '1' then

                        exception_cause <= std_logic_vector(unsigned(CSR_CAUSE_IRQ_BASE) + unsigned(irq_asserted_num));

                elsif decode_exception = '1' then

                        exception_cause <= decode_exception_cause;

                elsif mem_op = MEMOP_TYPE_INVALID then

                        exception_cause <= CSR_CAUSE_INVALID_INSTR;

                elsif instr_misaligned = '1' then

                        exception_cause <= CSR_CAUSE_INSTR_MISALIGN;

                elsif data_misaligned = '1' and mem_op = MEMOP_TYPE_STORE then

                        exception_cause <= CSR_CAUSE_STORE_MISALIGN;

                elsif data_misaligned = '1' and memop_is_load(mem_op) then

                        exception_cause <= CSR_CAUSE_LOAD_MISALIGN;

                else

                        exception_cause <= CSR_CAUSE_NONE;

                end if;

        end process find_exception_cause;

        find_exception_vaddr: process(instr_misaligned, data_misaligned, jump_target, alu_result)

        begin

                if instr_misaligned = '1' then

                        exception_vaddr <= jump_target;

                elsif data_misaligned = '1' then

                        exception_vaddr <= alu_result;

                else

                        exception_vaddr <= (others => '0');

                end if;

        end process find_exception_vaddr;

        calc_jump_tgt: process(branch, pc, rs1_forwarded, immediate, csr_value_forwarded)

        begin

                case branch is

                        when BRANCH_JUMP | BRANCH_CONDITIONAL =>

                                jump_target <= std_logic_vector(unsigned(pc) + unsigned(immediate));

                        when BRANCH_JUMP_INDIRECT =>

                                jump_target <= std_logic_vector(unsigned(rs1_forwarded) + unsigned(immediate));

                        when BRANCH_SRET =>

                                jump_target <= csr_value_forwarded; -- Will be the EPC value in the case of SRET

                        when others =>

                                jump_target <= (others => '0');

                end case;

        end process calc_jump_tgt;

        alu_x_mux: entity work.pp_alu_mux

                port map(

                        source => alu_x_src,

                        register_value => rs1_forwarded,

                        immediate_value => immediate,

                        shamt_value => shamt,

                        pc_value => pc,

                        csr_value => csr_value_forwarded,

                        output => alu_x

                );

        alu_y_mux: entity work.pp_alu_mux

                port map(

                        source => alu_y_src,

                        register_value => rs2_forwarded,

                        immediate_value => immediate,

                        shamt_value => shamt,

                        pc_value => pc,

                        csr_value => csr_value_forwarded,

                        output => alu_y

                );

        alu_x_forward: process(mem_rd_write, mem_rd_value, mem_rd_addr, rs1_addr,

                rs1_data, wb_rd_write, wb_rd_addr, wb_rd_value)

        begin

                if mem_rd_write = '1' and mem_rd_addr = rs1_addr and mem_rd_addr /= b"00000" then

                        rs1_forwarded <= mem_rd_value;

                elsif wb_rd_write = '1' and wb_rd_addr = rs1_addr and wb_rd_addr /= b"00000" then

                        rs1_forwarded <= wb_rd_value;

                else

                        rs1_forwarded <= rs1_data;

                end if;

        end process alu_x_forward;

        alu_y_forward: process(mem_rd_write, mem_rd_value, mem_rd_addr, rs2_addr,

                rs2_data, wb_rd_write, wb_rd_addr, wb_rd_value)

        begin

                if mem_rd_write = '1' and mem_rd_addr = rs2_addr and mem_rd_addr /= b"00000" then

                        rs2_forwarded <= mem_rd_value;

                elsif wb_rd_write = '1' and wb_rd_addr = rs2_addr and wb_rd_addr /= b"00000" then

                        rs2_forwarded <= wb_rd_value;

                else

                        rs2_forwarded <= rs2_data;

                end if;

        end process alu_y_forward;

        csr_forward: process(mem_csr_write, wb_csr_write, csr_addr, mem_csr_addr, wb_csr_addr,

                csr_value, mem_csr_value, wb_csr_value, csr_writeable, mem_exception, wb_exception,

                mem_exception_context, wb_exception_context)

        begin

                if csr_addr = CSR_CAUSE and mem_exception = '1' then

                        csr_value_forwarded <= to_std_logic_vector(mem_exception_context.cause);

                elsif csr_addr = CSR_STATUS and mem_exception = '1' then

                        csr_value_forwarded <= to_std_logic_vector(mem_exception_context.status);

                elsif csr_addr = CSR_BADVADDR and mem_exception = '1' then

                        csr_value_forwarded <= mem_exception_context.badvaddr;

                elsif mem_csr_write /= CSR_WRITE_NONE and mem_csr_addr = csr_addr and csr_writeable then

                        csr_value_forwarded <= mem_csr_value;

                elsif csr_addr = CSR_CAUSE and wb_exception = '1' then

                        csr_value_forwarded <= to_std_logic_vector(wb_exception_context.cause);

                elsif csr_addr = CSR_STATUS and wb_exception = '1' then

                        csr_value_forwarded <= to_std_logic_vector(wb_exception_context.status);

                elsif csr_addr = CSR_BADVADDR and wb_exception = '1' then

                        csr_value_forwarded <= wb_exception_context.badvaddr;

                elsif wb_csr_write /= CSR_WRITE_NONE and wb_csr_addr = csr_addr and csr_writeable then

                        csr_value_forwarded <= wb_csr_value;

                else

                        csr_value_forwarded <= csr_value;

                end if;

        end process csr_forward;

        evec_forward: process(mem_csr_write, mem_csr_addr, mem_csr_value,

                wb_csr_write, wb_csr_addr, wb_csr_value, evec)

        begin

                if mem_csr_write /= CSR_WRITE_NONE and mem_csr_addr = CSR_EVEC then

                        evec_forwarded <= mem_csr_value;

                elsif wb_csr_write /= CSR_WRITE_NONE and wb_csr_addr = CSR_EVEC then

                        evec_forwarded <= wb_csr_value;

                else

                        evec_forwarded <= evec;

                end if;

        end process evec_forward;

        exception_ctx_forward: process(mem_exception, wb_exception, mem_exception_context, wb_exception_context,

                exception_cause, exception_vaddr, mem_csr_write, mem_csr_addr, mem_csr_value,

                wb_csr_write, wb_csr_addr, wb_csr_value, sr)

        begin

                if mem_exception = '1' then

                        exception_context_forwarded <= mem_exception_context;

                elsif mem_csr_write /= CSR_WRITE_NONE and mem_csr_addr = CSR_STATUS then

                        exception_context_forwarded <= (

                                status => to_csr_status_register(mem_csr_value),

                                cause => mem_exception_context.cause,

                                badvaddr => mem_exception_context.badvaddr);

                elsif wb_exception = '1' then

                        exception_context_forwarded <= wb_exception_context;

                elsif wb_csr_write /= CSR_WRITE_NONE and wb_csr_addr = CSR_STATUS then

                        exception_context_forwarded <= (

                                status => to_csr_status_register(wb_csr_value),

                                cause => wb_exception_context.cause,

                                badvaddr => wb_exception_context.badvaddr);

                else

                        exception_context_forwarded.status <= sr;

                        exception_context_forwarded.cause <= exception_cause;

                        exception_context_forwarded.badvaddr <= exception_vaddr;

                end if;

        end process exception_ctx_forward;

        detect_load_hazard: process(mem_mem_op, mem_rd_addr, rs1_addr, rs2_addr,

                alu_x_src, alu_y_src)

        begin

                if (mem_mem_op = MEMOP_TYPE_LOAD or mem_mem_op = MEMOP_TYPE_LOAD_UNSIGNED) and

                                ((alu_x_src = ALU_SRC_REG and mem_rd_addr = rs1_addr and rs1_addr /= b"00000")

                        or

                                (alu_y_src = ALU_SRC_REG and mem_rd_addr = rs2_addr and rs2_addr /= b"00000"))

                then

                        hazard_detected <= '1';

                else

                        hazard_detected <= '0';

                end if;

        end process detect_load_hazard;

        branch_comparator: entity work.pp_comparator

                port map(

                        funct3 => funct3,

                        rs1 => rs1_forwarded,

                        rs2 => rs2_forwarded,

                        result => branch_condition

                );

        alu_instance: entity work.pp_alu

                port map(

                        result => alu_result,

                        x => alu_x,

                        y => alu_y,

                        operation => alu_op

                );

        csr_alu_instance: entity work.pp_csr_alu

                port map(

                        x => csr_value_forwarded,

                        y => rs1_forwarded,

                        result => csr_value_out,

                        immediate => rs1_addr,

                        use_immediate => csr_use_immediate,

                        write_mode => csr_write

                );

end architecture behaviour;