Subversion Repositories rv01_riscv_core

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-- Copyright (C) 2015 Stefano Tonello                          --

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---------------------------------------------------------------

-- RV01 result forwarding logic

---------------------------------------------------------------

library IEEE;

use IEEE.std_logic_1164.all;

use IEEE.numeric_std.all;

use STD.textio.all;

library work;

use work.RV01_CONSTS_PKG.all;

use work.RV01_TYPES_PKG.all;

use work.RV01_IDEC_PKG.all;

entity RV01_FWDLOG_2W_P6 is

  port(

    ID_RX_i : in RID_T;

    ID_RRX_i : in std_logic;

    IX1_INSTR0_i : in DEC_INSTR_T;

    IX2_INSTR0_i : in DEC_INSTR_T;

    IX3_INSTR0_i : in DEC_INSTR_T;

    IX1_INSTR1_i : in DEC_INSTR_T;

    IX2_INSTR1_i : in DEC_INSTR_T;

    IX3_INSTR1_i : in DEC_INSTR_T;

    IX1_PA_RES0_i : in SDWORD_T;

    IX1_PA_RES1_i : in SDWORD_T;

    IX2_PA_RES0_i : in SDWORD_T;

    IX2_PA_RES1_i : in SDWORD_T;

    IX3_PA_RES0_i : in SDWORD_T;

    IX3_PA_RES1_i : in SDWORD_T;

    ID_OPX_NOFWD_i : in SDWORD_T;

    IX1_V_i : in std_logic_vector(2-1 downto 0);

    IX2_V_i : in std_logic_vector(2-1 downto 0);

    IX3_V_i : in std_logic_vector(2-1 downto 0);

    IX1_FWDE_i : in std_logic_vector(2-1 downto 0);

    IX2_FWDE_i : in std_logic_vector(2-1 downto 0);

    IX3_FWDE_i : in std_logic_vector(2-1 downto 0);

    NOREGS_i : in std_logic;

    NOREGD_i : in SDWORD_T;

    ID_OPX_o : out SDWORD_T

  );

end RV01_FWDLOG_2W_P6;

architecture ARC of RV01_FWDLOG_2W_P6 is

  constant SZERO : SDWORD_T := (others => '0');

begin

  -- Operand A can be forwarded from stages IX and MA.

  -- When forwarding from IX stage, result can come from

  -- ALU single-cycle result output or from LSU read data output.

  -- When forwarding from MA stage, result can come from

  -- ALU double-cycle result output only.

  -- WARNING: it's assumed that *_INSTR.RD always differs from

  -- *_INSTR_RD2 because a register can be written only once per

  -- cycle. If this condition is not satisfied ASIP behavior is

  -- undefined.

  process(ID_RX_i,ID_RRX_i,

    IX1_INSTR0_i,IX2_INSTR0_i,IX1_INSTR1_i,IX2_INSTR1_i,

    IX3_INSTR0_i,IX3_INSTR1_i,

    IX1_PA_RES0_i,IX1_PA_RES1_i,IX2_PA_RES0_i,IX2_PA_RES1_i,

    IX3_PA_RES0_i,IX3_PA_RES1_i,

    ID_OPX_NOFWD_i,IX1_V_i,IX2_V_i,IX3_V_i,

    IX1_FWDE_i,IX2_FWDE_i,IX3_FWDE_i,

    NOREGS_i,NOREGD_i)

    variable FWD_IX : std_logic_vector(5 downto 0);

  begin

    -- forwarding from IX1 stage occurs if:

    -- 1) ID stage instr. rA matches IX1 stage instr. rD AND

    -- 2) ID stage instr. reads rA AND

    -- 3) IX1 stage instr. writes rD AND

    -- 4) ID stage instr. is valid (IX1 stage one always is), AND

    -- 5) IX1 instr. is forward-enabled

    if(ID_RX_i = IX1_INSTR0_i.RD) then

      FWD_IX(0) := IX1_INSTR0_i.WRD and IX1_V_i(0) and

        IX1_FWDE_i(0); -- and ID_RRX_i;

    else

      FWD_IX(0) := '0';

    end if;

    if(ID_RX_i = IX1_INSTR1_i.RD) then

      FWD_IX(1) := IX1_INSTR1_i.WRD and IX1_V_i(1) and

        IX1_FWDE_i(1); -- and ID_RRX_i;

    else

      FWD_IX(1) := '0';

    end if;

    -- forwarding from IX2 stage occurs if:

    -- 1) ID stage instr. rA matches IX2 stage instr. rD AND

    -- 2) ID stage instr. reads rA AND

    -- 3) IX2 stage instr. writes rD AND

    -- 4) ID stage instr. is valid (IX1 stage one always is), AND

    -- 5) IX2 instr. is forward-enabled

    if(ID_RX_i = IX2_INSTR0_i.RD) then

      FWD_IX(2) := IX2_INSTR0_i.WRD and IX2_V_i(0) and

        IX2_FWDE_i(0); -- and ID_RRX_i;

    else

      FWD_IX(2) := '0';

    end if;

    if(ID_RX_i = IX2_INSTR1_i.RD) then

      FWD_IX(3) := IX2_INSTR1_i.WRD and IX2_V_i(1) and

        IX2_FWDE_i(1); -- and ID_RRX_i;

    else

      FWD_IX(3) := '0';

    end if;

    -- forwarding from IX3 stage occurs if:

    -- 1) ID stage instr. rA matches IX3 stage instr. rD AND

    -- 2) ID stage instr. reads rA AND

    -- 3) IX3 stage instr. writes rD AND

    -- 4) ID stage instr. is valid (IX1 stage one always is), AND

    -- 5) IX3 instr. is forward-enabled

    if(ID_RX_i = IX3_INSTR0_i.RD) then

      FWD_IX(4) := IX3_INSTR0_i.WRD and IX3_V_i(0) and

        IX3_FWDE_i(0); -- and ID_RRX_i;

    else

      FWD_IX(4) := '0';

    end if;

    if(ID_RX_i = IX3_INSTR1_i.RD) then

      FWD_IX(5) := IX3_INSTR1_i.WRD and IX3_V_i(1) and

        IX3_FWDE_i(1); -- and ID_RRX_i;

    else

      FWD_IX(5) := '0';

    end if;

    ---- result forwarding mux

    --if(FWD_IX(0) = '1' and ID_RRX_i = '1') then

    --  ID_OPX_o <= SZERO & IX1_PA_RES0_i;

    --elsif(FWD_IX(1) = '1' and ID_RRX_i = '1') then

    --  ID_OPX_o <= SZERO & IX1_PA_RES1_i;

    --elsif(FWD_IX(2) = '1' and ID_RRX_i = '1') then

    --  ID_OPX_o <= IX2_PA_RES0_i;

    --elsif(FWD_IX(3) = '1' and ID_RRX_i = '1') then

    --  ID_OPX_o <= IX2_PA_RES1_i;

    --elsif((FWD_IX(4) = '0' and FWD_IX(5) = '0') or ID_RRX_i = '0') then

    --  if(NOREGS_i = '0') then

    --    ID_OPX_o <= ID_OPX_NOFWD_i; -- give higher priority to RF output

    --  else

    --    ID_OPX_o <= NOREGD_i;

    --  end if;

    --elsif(FWD_IX(4) = '1' and ID_RRX_i = '1') then

    --  ID_OPX_o <= IX3_PA_RES0_i;

    --else --elsif(FWD_IX(5) = '1' and ID_RRX_i = '1') then

    --  ID_OPX_o <= IX3_PA_RES1_i;

    ----else

    ----  ID_OPX_o <= ID_OPX_NOFWD_i;

    --end if;

    -- result forwarding mux

    if(FWD_IX(1) = '1' and NOREGS_i = '0') then

      ID_OPX_o <= IX1_PA_RES1_i;

    elsif(FWD_IX(0) = '1' and NOREGS_i = '0') then

      ID_OPX_o <= IX1_PA_RES0_i;

    elsif(FWD_IX(3) = '1' and NOREGS_i = '0') then

      ID_OPX_o <= IX2_PA_RES1_i;

    elsif(FWD_IX(2) = '1' and NOREGS_i = '0') then

      ID_OPX_o <= IX2_PA_RES0_i;

    elsif((FWD_IX(4) = '0' and FWD_IX(5) = '0') and NOREGS_i = '0') then

        ID_OPX_o <= ID_OPX_NOFWD_i; -- give higher priority to RF output

    elsif(NOREGS_i = '1') then

        ID_OPX_o <= NOREGD_i;

    elsif(FWD_IX(5) = '1') then -- and NOREGS_i = '0') then

      ID_OPX_o <= IX3_PA_RES1_i;

    else --elsif(FWD_IX(4) = '1' and NOREGS_i = '0') then

      ID_OPX_o <= IX3_PA_RES0_i;

    --else

    --  ID_OPX_o <= ID_OPX_NOFWD_i;

    end if;

  end process;

end ARC;