Subversion Repositories rv01_riscv_core

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-- Copyright (C) 2017 Stefano Tonello                          --

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-- A-pipeline result mux (IX2 stage)

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

library IEEE;

use IEEE.std_logic_1164.all;

use IEEE.numeric_std.all;

library WORK;

use WORK.RV01_CONSTS_PKG.all;

use WORK.RV01_TYPES_PKG.all;

use WORK.RV01_FUNCS_PKG.all;

use work.RV01_IDEC_PKG.all;

entity RV01_PIPE_A_RMX_X2 is

  generic(

    NW : natural := 2

  );

  port(

    OPA_V_i :  in std_logic;

    OPB_V_i :  in std_logic;

    OPA_i : in SDWORD_T;

    OPB_i : in SDWORD_T;

    INSTR_i : in DEC_INSTR_T;

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

    IX3_INSTR_i : in DEC_INSTR_VEC_T(NW-1 downto 0);

    IX3_RES0_i : in SDWORD_T;

    IX3_RES1_i : in SDWORD_T;

    OPA_V_o :  out std_logic;

    OPB_V_o :  out std_logic;

    OPA_o : out SDWORD_T;

    OPB_o : out SDWORD_T

  );

end RV01_PIPE_A_RMX_X2;

architecture ARC of RV01_PIPE_A_RMX_X2 is

  signal SELA1,SELB1 : std_logic;

  signal UOPA,UOPB : SDWORD_T;

  signal UOPA_V,UOPB_V : std_logic;

begin

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

  -- Notes

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

  -- Stage IX3 provides (up to) two results per cycle,

  -- requiring a mux to select the desired one.

  -- OPA source selection flag

  SELA1 <= IX3_V_i(1) when (

    IX3_INSTR_i(1).WRD = '1' and

    IX3_INSTR_i(1).RD = INSTR_i.RS1

  ) else '0';

  -- Updated OPA operand source mux

  UOPA <= IX3_RES1_i when (SELA1 = '1') else IX3_RES0_i;

  -- Updated OPA operand valid flag (flag is set if there's

  -- a valid value for it from IX3 stage).

  UOPA_V <=  '1' when (

    (

      IX3_V_i(0) = '1' and

      IX3_INSTR_i(0).WRD = '1' and

      IX3_INSTR_i(0).RD = INSTR_i.RS1

     ) or (

      IX3_V_i(1) = '1' and

      IX3_INSTR_i(1).WRD = '1' and

      IX3_INSTR_i(1).RD = INSTR_i.RS1

     )

  ) else '0';

  -- OPB source selection flag

  SELB1 <= IX3_V_i(1) when (

    IX3_INSTR_i(1).WRD = '1' and

    IX3_INSTR_i(1).RD = INSTR_i.RS2

  ) else '0';

  -- Updated OPB operand source mux

  UOPB <= IX3_RES1_i when (SELB1 = '1') else IX3_RES0_i;

  -- Updated OPB operand valid flag (flag is set if there's

  -- a valid value for it from IX3 stage).

  UOPB_V <= '1' when (

    (

      IX3_V_i(0) = '1' and

      IX3_INSTR_i(0).WRD = '1' and

      IX3_INSTR_i(0).RD = INSTR_i.RS2

     ) or (

      IX3_V_i(1) = '1' and

      IX3_INSTR_i(1).WRD = '1' and

      IX3_INSTR_i(1).RD = INSTR_i.RS2

     )

  ) else '0';

  OPA_V_o <= OPA_V_i or UOPA_V;

  OPB_V_o <= OPB_V_i or UOPB_V;

  OPA_o <= OPA_i when (OPA_V_i = '1') else UOPA;

  OPB_o <= OPB_i when (OPB_V_i = '1') else UOPB;

end ARC;