decode2.vhdl

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

library work;
use work.decode_types.all;
use work.common.all;
use work.helpers.all;
use work.insn_helpers.all;

entity decode2 is
    generic (
        EX1_BYPASS : boolean := true
        );
    port (
        clk   : in std_ulogic;
        rst   : in std_ulogic;

        complete_in : in std_ulogic;
        stall_in : in std_ulogic;
        stall_out : out std_ulogic;

        stopped_out : out std_ulogic;

        flush_in: in std_ulogic;

        d_in  : in Decode1ToDecode2Type;

        e_out : out Decode2ToExecute1Type;

        r_in  : in RegisterFileToDecode2Type;
        r_out : out Decode2ToRegisterFileType;

        c_in  : in CrFileToDecode2Type;
        c_out : out Decode2ToCrFileType
	);
end entity decode2;

architecture behaviour of decode2 is
    type reg_type is record
        e : Decode2ToExecute1Type;
    end record;

    signal r, rin : reg_type;

    type decode_input_reg_t is record
        reg_valid : std_ulogic;
        reg       : gspr_index_t;
        data      : std_ulogic_vector(63 downto 0);
    end record;

    type decode_output_reg_t is record
        reg_valid : std_ulogic;
        reg       : gspr_index_t;
    end record;

    function decode_input_reg_a (t : input_reg_a_t; insn_in : std_ulogic_vector(31 downto 0);
                                 reg_data : std_ulogic_vector(63 downto 0);
                                 ispr : gspr_index_t;
                                 instr_addr : std_ulogic_vector(63 downto 0))
        return decode_input_reg_t is
    begin
        if t = RA or (t = RA_OR_ZERO and insn_ra(insn_in) /= "00000") then
            assert is_fast_spr(ispr) = '0' report "Decode A says GPR but ISPR says SPR:" &
                to_hstring(ispr) severity failure;
            return ('1', gpr_to_gspr(insn_ra(insn_in)), reg_data);
        elsif t = SPR then
            -- ISPR must be either a valid fast SPR number or all 0 for a slow SPR.
            -- If it's all 0, we don't treat it as a dependency as slow SPRs
            -- operations are single issue.
            --
            assert is_fast_spr(ispr) =  '1' or ispr = "000000"
                report "Decode A says SPR but ISPR is invalid:" &
                to_hstring(ispr) severity failure;
            return (is_fast_spr(ispr), ispr, reg_data);
        elsif t = CIA then
            return ('0', (others => '0'), instr_addr);
        else
            return ('0', (others => '0'), (others => '0'));
        end if;
    end;

    function decode_input_reg_b (t : input_reg_b_t; insn_in : std_ulogic_vector(31 downto 0);
                                 reg_data : std_ulogic_vector(63 downto 0);
                                 ispr : gspr_index_t) return decode_input_reg_t is
        variable ret : decode_input_reg_t;
    begin
        case t is
            when RB =>
                assert is_fast_spr(ispr) = '0' report "Decode B says GPR but ISPR says SPR:" &
                    to_hstring(ispr) severity failure;
                ret := ('1', gpr_to_gspr(insn_rb(insn_in)), reg_data);
            when CONST_UI =>
                ret := ('0', (others => '0'), std_ulogic_vector(resize(unsigned(insn_ui(insn_in)), 64)));
            when CONST_SI =>
                ret := ('0', (others => '0'), std_ulogic_vector(resize(signed(insn_si(insn_in)), 64)));
            when CONST_SI_HI =>
                ret := ('0', (others => '0'), std_ulogic_vector(resize(signed(insn_si(insn_in)) & x"0000", 64)));
            when CONST_UI_HI =>
                ret := ('0', (others => '0'), std_ulogic_vector(resize(unsigned(insn_si(insn_in)) & x"0000", 64)));
            when CONST_LI =>
                ret := ('0', (others => '0'), std_ulogic_vector(resize(signed(insn_li(insn_in)) & "00", 64)));
            when CONST_BD =>
                ret := ('0', (others => '0'), std_ulogic_vector(resize(signed(insn_bd(insn_in)) & "00", 64)));
            when CONST_DS =>
                ret := ('0', (others => '0'), std_ulogic_vector(resize(signed(insn_ds(insn_in)) & "00", 64)));
            when CONST_DXHI4 =>
                ret := ('0', (others => '0'), std_ulogic_vector(resize(signed(insn_dx(insn_in)) & x"0004", 64)));
            when CONST_M1 =>
                ret := ('0', (others => '0'), x"FFFFFFFFFFFFFFFF");
            when CONST_SH =>
                ret := ('0', (others => '0'), x"00000000000000" & "00" & insn_in(1) & insn_in(15 downto 11));
            when CONST_SH32 =>
                ret := ('0', (others => '0'), x"00000000000000" & "000" & insn_in(15 downto 11));
            when SPR =>
                -- ISPR must be either a valid fast SPR number or all 0 for a slow SPR.
                -- If it's all 0, we don't treat it as a dependency as slow SPRs
                -- operations are single issue.
                assert is_fast_spr(ispr) = '1' or ispr = "000000"
                    report "Decode B says SPR but ISPR is invalid:" &
                    to_hstring(ispr) severity failure;
                ret := (is_fast_spr(ispr), ispr, reg_data);
            when NONE =>
                ret := ('0', (others => '0'), (others => '0'));
        end case;

        return ret;
    end;

    function decode_input_reg_c (t : input_reg_c_t; insn_in : std_ulogic_vector(31 downto 0);
                                 reg_data : std_ulogic_vector(63 downto 0)) return decode_input_reg_t is
    begin
        case t is
            when RS =>
                return ('1', gpr_to_gspr(insn_rs(insn_in)), reg_data);
            when NONE =>
                return ('0', (others => '0'), (others => '0'));
        end case;
    end;

    function decode_output_reg (t : output_reg_a_t; insn_in : std_ulogic_vector(31 downto 0);
                                ispr : gspr_index_t) return decode_output_reg_t is
    begin
        case t is
            when RT =>
                return ('1', gpr_to_gspr(insn_rt(insn_in)));
            when RA =>
                return ('1', gpr_to_gspr(insn_ra(insn_in)));
            when SPR =>
                -- ISPR must be either a valid fast SPR number or all 0 for a slow SPR.
                -- If it's all 0, we don't treat it as a dependency as slow SPRs
                -- operations are single issue.
                assert is_fast_spr(ispr) = '1' or ispr = "000000"
                    report "Decode B says SPR but ISPR is invalid:" &
                    to_hstring(ispr) severity failure;
                return (is_fast_spr(ispr), ispr);
            when NONE =>
                return ('0', "000000");
        end case;
    end;

    function decode_rc (t : rc_t; insn_in : std_ulogic_vector(31 downto 0)) return std_ulogic is
    begin
        case t is
            when RC =>
                return insn_rc(insn_in);
            when ONE =>
                return '1';
            when NONE =>
                return '0';
        end case;
    end;

    -- For now, use "rc" in the decode table to decide whether oe exists.
    -- This is not entirely correct architecturally: For mulhd and
    -- mulhdu, the OE field is reserved. It remains to be seen what an
    -- actual POWER9 does if we set it on those instructions, for now we
    -- test that further down when assigning to the multiplier oe input.
    --
    function decode_oe (t : rc_t; insn_in : std_ulogic_vector(31 downto 0)) return std_ulogic is
    begin
        case t is
            when RC =>
                return insn_oe(insn_in);
            when OTHERS =>
                return '0';
        end case;
    end;

    -- issue control signals
    signal control_valid_in : std_ulogic;
    signal control_valid_out : std_ulogic;
    signal control_sgl_pipe : std_logic;

    signal gpr_write_valid : std_ulogic;
    signal gpr_write : gspr_index_t;
    signal gpr_bypassable  : std_ulogic;

    signal gpr_a_read_valid : std_ulogic;
    signal gpr_a_read :gspr_index_t;
    signal gpr_a_bypass : std_ulogic;

    signal gpr_b_read_valid : std_ulogic;
    signal gpr_b_read : gspr_index_t;
    signal gpr_b_bypass : std_ulogic;

    signal gpr_c_read_valid : std_ulogic;
    signal gpr_c_read : gpr_index_t;
    signal gpr_c_bypass : std_ulogic;

    signal cr_write_valid : std_ulogic;
begin
    control_0: entity work.control
	generic map (
            PIPELINE_DEPTH => 1
            )
	port map (
            clk         => clk,
            rst         => rst,

            complete_in => complete_in,
            valid_in    => control_valid_in,
            stall_in    => stall_in,
            flush_in    => flush_in,
            sgl_pipe_in => control_sgl_pipe,
            stop_mark_in => d_in.stop_mark,

            gpr_write_valid_in => gpr_write_valid,
            gpr_write_in       => gpr_write,
            gpr_bypassable     => gpr_bypassable,

            gpr_a_read_valid_in  => gpr_a_read_valid,
            gpr_a_read_in        => gpr_a_read,

            gpr_b_read_valid_in  => gpr_b_read_valid,
            gpr_b_read_in        => gpr_b_read,

            gpr_c_read_valid_in  => gpr_c_read_valid,
            gpr_c_read_in        => gpr_c_read,

            cr_read_in           => d_in.decode.input_cr,
            cr_write_in           => cr_write_valid,

            valid_out   => control_valid_out,
            stall_out   => stall_out,
            stopped_out => stopped_out,

            gpr_bypass_a => gpr_a_bypass,
            gpr_bypass_b => gpr_b_bypass,
            gpr_bypass_c => gpr_c_bypass
            );

    decode2_0: process(clk)
    begin
        if rising_edge(clk) then
            if rin.e.valid = '1' then
                report "execute " & to_hstring(rin.e.nia);
            end if;
            r <= rin;
        end if;
    end process;

    r_out.read1_reg <= gpr_or_spr_to_gspr(insn_ra(d_in.insn), d_in.ispr1);
    r_out.read2_reg <= gpr_or_spr_to_gspr(insn_rb(d_in.insn), d_in.ispr2);
    r_out.read3_reg <= insn_rs(d_in.insn);

    c_out.read <= d_in.decode.input_cr;

    decode2_1: process(all)
        variable v : reg_type;
        variable mul_a : std_ulogic_vector(63 downto 0);
        variable mul_b : std_ulogic_vector(63 downto 0);
        variable decoded_reg_a : decode_input_reg_t;
        variable decoded_reg_b : decode_input_reg_t;
        variable decoded_reg_c : decode_input_reg_t;
        variable decoded_reg_o : decode_output_reg_t;
        variable length : std_ulogic_vector(3 downto 0);
    begin
        v := r;

        v.e := Decode2ToExecute1Init;

        mul_a := (others => '0');
        mul_b := (others => '0');

        --v.e.input_cr := d_in.decode.input_cr;
        --v.e.output_cr := d_in.decode.output_cr;
        
        decoded_reg_a := decode_input_reg_a (d_in.decode.input_reg_a, d_in.insn, r_in.read1_data, d_in.ispr1,
                                             d_in.nia);
        decoded_reg_b := decode_input_reg_b (d_in.decode.input_reg_b, d_in.insn, r_in.read2_data, d_in.ispr2);
        decoded_reg_c := decode_input_reg_c (d_in.decode.input_reg_c, d_in.insn, r_in.read3_data);
        decoded_reg_o := decode_output_reg (d_in.decode.output_reg_a, d_in.insn, d_in.ispr1);

        r_out.read1_enable <= decoded_reg_a.reg_valid and d_in.valid;
        r_out.read2_enable <= decoded_reg_b.reg_valid and d_in.valid;
        r_out.read3_enable <= decoded_reg_c.reg_valid and d_in.valid;

        case d_in.decode.length is
            when is1B =>
                length := "0001";
            when is2B =>
                length := "0010";
            when is4B =>
                length := "0100";
            when is8B =>
                length := "1000";
            when NONE =>
                length := "0000";
        end case;

        -- execute unit
        v.e.nia := d_in.nia;
        v.e.unit := d_in.decode.unit;
        v.e.insn_type := d_in.decode.insn_type;
        v.e.read_reg1 := decoded_reg_a.reg;
        v.e.read_data1 := decoded_reg_a.data;
        v.e.bypass_data1 := gpr_a_bypass;
        v.e.read_reg2 := decoded_reg_b.reg;
        v.e.read_data2 := decoded_reg_b.data;
        v.e.bypass_data2 := gpr_b_bypass;
        v.e.read_data3 := decoded_reg_c.data;
        v.e.bypass_data3 := gpr_c_bypass;
        v.e.write_reg := decoded_reg_o.reg;
        v.e.rc := decode_rc(d_in.decode.rc, d_in.insn);
        if not (d_in.decode.insn_type = OP_MUL_H32 or d_in.decode.insn_type = OP_MUL_H64) then
            v.e.oe := decode_oe(d_in.decode.rc, d_in.insn);
        end if;
        v.e.cr := c_in.read_cr_data;
        v.e.xerc := c_in.read_xerc_data;
        v.e.invert_a := d_in.decode.invert_a;
        v.e.invert_out := d_in.decode.invert_out;
        v.e.input_carry := d_in.decode.input_carry;
        v.e.output_carry := d_in.decode.output_carry;
        v.e.is_32bit := d_in.decode.is_32bit;
        v.e.is_signed := d_in.decode.is_signed;
        if d_in.decode.lr = '1' then
            v.e.lr := insn_lk(d_in.insn);
        end if;
        v.e.insn := d_in.insn;
        v.e.data_len := length;
        v.e.byte_reverse := d_in.decode.byte_reverse;
        v.e.sign_extend := d_in.decode.sign_extend;
        v.e.update := d_in.decode.update;
        v.e.reserve := d_in.decode.reserve;

        -- issue control
        control_valid_in <= d_in.valid;
        control_sgl_pipe <= d_in.decode.sgl_pipe;

        gpr_write_valid <= decoded_reg_o.reg_valid;
        gpr_write <= decoded_reg_o.reg;
        gpr_bypassable <= '0';
        if EX1_BYPASS and d_in.decode.unit = ALU then
            gpr_bypassable <= '1';
        end if;

        gpr_a_read_valid <= decoded_reg_a.reg_valid;
        gpr_a_read <= decoded_reg_a.reg;

        gpr_b_read_valid <= decoded_reg_b.reg_valid;
        gpr_b_read <= decoded_reg_b.reg;

        gpr_c_read_valid <= decoded_reg_c.reg_valid;
        gpr_c_read <= gspr_to_gpr(decoded_reg_c.reg);

        cr_write_valid <= d_in.decode.output_cr or decode_rc(d_in.decode.rc, d_in.insn);

        v.e.valid := control_valid_out;
        if d_in.decode.unit = NONE then
            v.e.insn_type := OP_ILLEGAL;
        end if;

        if rst = '1' then
            v.e := Decode2ToExecute1Init;
        end if;

        -- Update registers
        rin <= v;

        -- Update outputs
        e_out <= r.e;
    end process;
end architecture behaviour;