Subversion Repositories neorv32

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

-- # << NEORV32 - CPU General Purpose Data Register File >>                                        #

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

-- # General purpose data register file. 32 entries (= 1024 bit) for normal mode (RV32I),          #

-- # 16 entries (= 512 bit) for embedded mode (RV32E) when RISC-V "E" extension is enabled.        #

-- #                                                                                               #

-- # Register zero (r0/x0) is a "normal" physical reg that has to be initialized to zero by the    #

-- # CPU control system. For normal operations register zero cannot be written.                    #

-- #                                                                                               #

-- # The register file uses synchronous read accesses and a *single* (multiplexed) address port    #

-- # for writing and reading rs1 and a single read-only port for rs2. Therefore, the whole         #

-- # register file can be mapped to a single true dual-port block RAM.                             #

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

-- # BSD 3-Clause License                                                                          #

-- #                                                                                               #

-- # Copyright (c) 2021, 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    #

-- # AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING     #

-- # NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED  #

-- # 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 -- 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

    -- 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

    cmp_o  : out std_ulogic_vector(1 downto 0) -- comparator status

  );

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

  signal rd_is_r0     : std_ulogic; -- writing to r0?

  signal dst_addr     : std_ulogic_vector(4 downto 0); -- destination address

  signal opa_addr     : std_ulogic_vector(4 downto 0); -- rs1/dst address

  signal opb_addr     : std_ulogic_vector(4 downto 0); -- rs2 address

  signal rs1, rs2     : std_ulogic_vector(data_width_c-1 downto 0); -- read data

  -- comparator --

  signal cmp_opx : std_ulogic_vector(data_width_c downto 0);

  signal cmp_opy : std_ulogic_vector(data_width_c downto 0);

begin

  -- Data Input Mux -------------------------------------------------------------------------

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

  input_mux: process(rd_is_r0, ctrl_i, alu_i, mem_i)

  begin

    if (rd_is_r0 = '1') then -- write zero if accessing x0 to "emulate" it is hardwired to zero

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

    else

      if (ctrl_i(ctrl_rf_in_mux_c) = '0') then

        rf_wdata <= alu_i;

      else

        rf_wdata <= mem_i;

      end if;

    end if;

  end process input_mux;

  -- check if we are writing to x0 --

  rd_is_r0 <= (not or_reduce_f(dst_addr(4 downto 0))) when (CPU_EXTENSION_RISCV_E = false) else (not or_reduce_f(dst_addr(3 downto 0)));

  -- Register File 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

        if (ctrl_i(ctrl_rf_wb_en_c) = '1') then

          reg_file(to_integer(unsigned(opa_addr(4 downto 0)))) <= rf_wdata;

        end if;

        rs1 <= reg_file(to_integer(unsigned(opa_addr(4 downto 0))));

        rs2 <= reg_file(to_integer(unsigned(opb_addr(4 downto 0))));

      else -- embedded register file with 16 entries

        if (ctrl_i(ctrl_rf_wb_en_c) = '1') then

          reg_file_emb(to_integer(unsigned(opa_addr(3 downto 0)))) <= rf_wdata;

        end if;

        rs1 <= reg_file_emb(to_integer(unsigned(opa_addr(3 downto 0))));

        rs2 <= reg_file_emb(to_integer(unsigned(opb_addr(3 downto 0))));

      end if;

    end if;

  end process rf_access;

  -- access addresses --

  dst_addr <= ctrl_i(ctrl_rf_rd_adr4_c downto ctrl_rf_rd_adr0_c);

  opa_addr <= dst_addr when (ctrl_i(ctrl_rf_wb_en_c) = '1') else ctrl_i(ctrl_rf_rs1_adr4_c downto ctrl_rf_rs1_adr0_c); -- rd/rs1

  opb_addr <= ctrl_i(ctrl_rf_rs2_adr4_c downto ctrl_rf_rs2_adr0_c); -- rs2

  -- data output --

  rs1_o <= rs1;

  rs2_o <= rs2;

  -- Comparator Unit (for conditional branches) ---------------------------------------------

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

  cmp_opx <= (rs1(rs1'left) and (not ctrl_i(ctrl_alu_unsigned_c))) & rs1;

  cmp_opy <= (rs2(rs2'left) and (not ctrl_i(ctrl_alu_unsigned_c))) & rs2;

  cmp_o(cmp_equal_c) <= '1' when (rs1 = rs2) else '0';

  cmp_o(cmp_less_c)  <= '1' when (signed(cmp_opx) < signed(cmp_opy)) else '0';

end neorv32_cpu_regfile_rtl;