Subversion Repositories neorv32

-- #################################################################################################

-- # << NEORV32 - CPU Register File >>                                                             #

-- # ********************************************************************************************* #

-- # General purpose data registers. 32 entries for normal mode, 16 entries for embedded mode when #

-- # RISC-V M extension is enabled. x0 output is allways set to zero.                              #

-- # ********************************************************************************************* #

-- # BSD 3-Clause License                                                                          #

-- #                                                                                               #

-- # Copyright (c) 2020, Stephan Nolting. All rights reserved.                                     #

-- #                                                                                               #

-- # Redistribution and use in source and binary forms, with or without modification, are          #

-- # permitted provided that the following conditions are met:                                     #

-- #                                                                                               #

-- # 1. Redistributions of source code must retain the above copyright notice, this list of        #

-- #    conditions and the following disclaimer.                                                   #

-- #                                                                                               #

-- # 2. Redistributions in binary form must reproduce the above copyright notice, this list of     #

-- #    conditions and the following disclaimer in the documentation and/or other materials        #

-- #    provided with the distribution.                                                            #

-- #                                                                                               #

-- # 3. Neither the name of the copyright holder nor the names of its contributors may be used to  #

-- #    endorse or promote products derived from this software without specific prior written      #

-- #    permission.                                                                                #

-- #                                                                                               #

-- # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS   #

-- # OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF               #

-- # MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE    #

-- # COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,     #

-- # EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE #

-- # GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED    #

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-- # OF THE POSSIBILITY OF SUCH DAMAGE.                                                            #

-- # ********************************************************************************************* #

-- # The NEORV32 Processor - https://github.com/stnolting/neorv32              (c) Stephan Nolting #

-- #################################################################################################

library ieee;

use ieee.std_logic_1164.all;

use ieee.numeric_std.all;

library neorv32;

use neorv32.neorv32_package.all;

entity neorv32_cpu_regfile is

  generic (

    CPU_EXTENSION_RISCV_E : boolean := false -- implement embedded RF extension?

  );

  port (

    -- global control --

    clk_i  : in  std_ulogic; -- global clock, rising edge

    ctrl_i : in  std_ulogic_vector(ctrl_width_c-1 downto 0); -- main control bus

    -- data input --

    mem_i  : in  std_ulogic_vector(data_width_c-1 downto 0); -- memory read data

    alu_i  : in  std_ulogic_vector(data_width_c-1 downto 0); -- ALU result

    csr_i  : in  std_ulogic_vector(data_width_c-1 downto 0); -- CSR read data

    pc_i   : in  std_ulogic_vector(data_width_c-1 downto 0); -- current pc

    -- data output --

    rs1_o  : out std_ulogic_vector(data_width_c-1 downto 0); -- operand 1

    rs2_o  : out std_ulogic_vector(data_width_c-1 downto 0)  -- operand 2

  );

end neorv32_cpu_regfile;

architecture neorv32_cpu_regfile_rtl of neorv32_cpu_regfile is

  -- register file --

  type   reg_file_t is array (31 downto 0) of std_ulogic_vector(data_width_c-1 downto 0);

  type   reg_file_emb_t is array (15 downto 0) of std_ulogic_vector(data_width_c-1 downto 0);

  signal reg_file      : reg_file_t;

  signal reg_file_emb  : reg_file_emb_t;

  signal rf_write_data : std_ulogic_vector(data_width_c-1 downto 0); -- actual write-back data

  signal valid_wr      : std_ulogic; -- writing not to r0

  signal rs1_read      : std_ulogic_vector(data_width_c-1 downto 0); -- internal operand rs1

  signal rs2_read      : std_ulogic_vector(data_width_c-1 downto 0); -- internal operand rs2

  -- reading from r0? --

  signal rs1_clear, rs2_clear : std_ulogic;

  -- attributes - these are *NOT mandatory*; just for footprint / timing optimization --

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

  -- lattice radiant --

  attribute syn_ramstyle : string;

  attribute syn_ramstyle of reg_file     : signal is "no_rw_check";

  attribute syn_ramstyle of reg_file_emb : signal is "no_rw_check";

  -- intel quartus prime --

  attribute ramstyle : string;

  attribute ramstyle of reg_file     : signal is "no_rw_check";

  attribute ramstyle of reg_file_emb : signal is "no_rw_check";

begin

  -- Input mux ------------------------------------------------------------------------------

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

  input_mux: process(ctrl_i, mem_i, alu_i, pc_i, csr_i)

  begin

    case ctrl_i(ctrl_rf_in_mux_msb_c downto ctrl_rf_in_mux_lsb_c) is

      when "00"   => rf_write_data <= alu_i;

      when "01"   => rf_write_data <= mem_i;

      when "10"   => rf_write_data <= pc_i;

      when others => rf_write_data <= csr_i;

    end case;

  end process input_mux;

  -- only write if destination is not x0 (pretty irrelevant, but might save some power) --

  valid_wr <= or_all_f(ctrl_i(ctrl_rf_rd_adr4_c downto ctrl_rf_rd_adr0_c)) when (CPU_EXTENSION_RISCV_E = false) else

              or_all_f(ctrl_i(ctrl_rf_rd_adr3_c downto ctrl_rf_rd_adr0_c));

  -- Register file read/write access --------------------------------------------------------

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

  rf_access: process(clk_i)

  begin

    if rising_edge(clk_i) then -- sync read and write

      if (CPU_EXTENSION_RISCV_E = false) then -- normal register file with 32 entries

        -- check if reading from r0 --

        rs1_clear <= '0';

        rs2_clear <= '0';

        if (ctrl_i(ctrl_rf_rs1_adr4_c downto ctrl_rf_rs1_adr0_c) = "00000") then

          rs1_clear <= '1';

        end if;

        if (ctrl_i(ctrl_rf_rs2_adr4_c downto ctrl_rf_rs2_adr0_c) = "00000") then

          rs2_clear <= '1';

        end if;

        -- write --

        if (ctrl_i(ctrl_rf_wb_en_c) = '1') and (valid_wr = '1') then -- valid write-back

          reg_file(to_integer(unsigned(ctrl_i(ctrl_rf_rd_adr4_c downto ctrl_rf_rd_adr0_c)))) <= rf_write_data;

        end if;

        -- read --

        rs1_read <= reg_file(to_integer(unsigned(ctrl_i(ctrl_rf_rs1_adr4_c downto ctrl_rf_rs1_adr0_c))));

        rs2_read <= reg_file(to_integer(unsigned(ctrl_i(ctrl_rf_rs2_adr4_c downto ctrl_rf_rs2_adr0_c))));

      else -- embedded register file with 16 entries

        -- check if reading from r0 --

        rs1_clear <= '0';

        rs2_clear <= '0';

        if (ctrl_i(ctrl_rf_rs1_adr3_c downto ctrl_rf_rs1_adr0_c) = "0000") then

          rs1_clear <= '1';

        end if;

        if (ctrl_i(ctrl_rf_rs2_adr3_c downto ctrl_rf_rs2_adr0_c) = "0000") then

          rs2_clear <= '1';

        end if;

        -- write --

        if (ctrl_i(ctrl_rf_wb_en_c) = '1') and (valid_wr = '1') then -- valid write-back

          reg_file_emb(to_integer(unsigned(ctrl_i(ctrl_rf_rd_adr3_c downto ctrl_rf_rd_adr0_c)))) <= rf_write_data;

        end if;

        -- read --

        rs1_read <= reg_file_emb(to_integer(unsigned(ctrl_i(ctrl_rf_rs1_adr3_c downto ctrl_rf_rs1_adr0_c))));

        rs2_read <= reg_file_emb(to_integer(unsigned(ctrl_i(ctrl_rf_rs2_adr3_c downto ctrl_rf_rs2_adr0_c))));

      end if;

    end if;

  end process rf_access;

  -- Check if reading from r0 ---------------------------------------------------------------

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

  rs1_o <= (others => '0') when ((rs1_clear or ctrl_i(ctrl_rf_clear_rs1_c)) = '1') else rs1_read;

  rs2_o <= (others => '0') when ((rs2_clear or ctrl_i(ctrl_rf_clear_rs2_c)) = '1') else rs2_read;

end neorv32_cpu_regfile_rtl;