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

-- TITLE: Register Bank

-- AUTHOR: Steve Rhoads (rhoadss@yahoo.com)

-- DATE CREATED: 2/2/01

-- FILENAME: reg_bank.vhd

-- PROJECT: MIPS CPU core

-- COPYRIGHT: Software placed into the public domain by the author.

--    Software 'as is' without warranty.  Author liable for nothing.

-- DESCRIPTION:

--    Implements a register bank with 32 registers that are 32-bits wide.

--    There are two read-ports and one write port.

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

use work.mips_pack.all;

entity reg_bank is

   port(clk            : in  std_logic;

        rs_index       : in  std_logic_vector(5 downto 0);

        rt_index       : in  std_logic_vector(5 downto 0);

        rd_index       : in  std_logic_vector(5 downto 0);

        reg_source_out : out std_logic_vector(31 downto 0);

        reg_target_out : out std_logic_vector(31 downto 0);

        reg_dest_new   : in  std_logic_vector(31 downto 0);

        intr_enable    : out std_logic);

end; --entity reg_bank

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

-- The ram_block architecture attempts to use TWO dual-port memories.

-- Different FPGAs and ASICs need different implementations.

-- Choose one of the RAM implementations below.

-- I need feedback on this section!

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

architecture ram_block of reg_bank is

   signal reg_status : std_logic;

   type ram_type is array(31 downto 0) of std_logic_vector(31 downto 0);

   --controls access to dual-port memories

   signal addr_a1, addr_a2, addr_b : std_logic_vector(4 downto 0);

   signal data_out1, data_out2     : std_logic_vector(31 downto 0);

   signal write_enable             : std_logic;

begin

reg_proc: process(clk, rs_index, rt_index, rd_index, reg_dest_new,

      reg_status, data_out1, data_out2)

begin

   --setup for first dual-port memory

   if rs_index = "101110" then  --reg_epc CP0 14

      addr_a1 <= "00000";

   else

      addr_a1 <= rs_index(4 downto 0);

   end if;

   case rs_index is

   when "000000" => reg_source_out <= ZERO;

   when "101100" => reg_source_out <= ZERO(31 downto 1) & reg_status;

   when "111111" => reg_source_out <= ZERO(31 downto 8) & "00110000"; --intr vector

   when others   => reg_source_out <= data_out1;

   end case;

   --setup for second dual-port memory

   addr_a2 <= rt_index(4 downto 0);

   case rt_index is

   when "000000" => reg_target_out <= ZERO;

   when others   => reg_target_out <= data_out2;

   end case;

   --setup second port (write port) for both dual-port memories

   if rd_index /= "000000" and rd_index /= "101100" then

      write_enable <= '1';

   else

      write_enable <= '0';

   end if;

   if rd_index = "101110" then  --reg_epc CP0 14

      addr_b <= "00000";

   else

      addr_b <= rd_index(4 downto 0);

   end if;

   if rising_edge(clk) then

      if rd_index = "101100" then

         reg_status <= reg_dest_new(0);

      elsif rd_index = "101110" then  --reg_epc CP0 14

         reg_status <= '0';           --disable interrupts

      end if;

   end if;

   intr_enable <= reg_status;

end process;

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

-- Pick only ONE of the dual-port RAM implementations below!

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

   -- Option #1

   -- One tri-port RAM, two read-ports, one write-port

   -- 32 registers 32-bits wide

   ram_proc: process(clk, addr_a1, addr_a2, addr_b, reg_dest_new,

         write_enable)

   variable tri_port_ram : ram_type;

   begin

      data_out1 <= tri_port_ram(conv_integer(addr_a1));

      data_out2 <= tri_port_ram(conv_integer(addr_a2));

      if rising_edge(clk) then

         if write_enable = '1' then

            tri_port_ram(conv_integer(addr_b)) := reg_dest_new;

         end if;

      end if;

   end process;

   -- Option #2

   -- Two dual-port RAMs, each with one read-port and one write-port

   -- According to the Xilinx answers database record #4075 this 

   -- architecture may cause Synplify to infer synchronous dual-port 

   -- RAM using RAM16x1D.  

--   ram_proc: process(clk, addr_a1, addr_a2, addr_b, reg_dest_new, 

--         write_enable)

--   variable dual_port_ram1 : ram_type;

--   variable dual_port_ram2 : ram_type;

--   begin

--      data_out1 <= dual_port_ram1(conv_integer(addr_a1));

--      data_out2 <= dual_port_ram2(conv_integer(addr_a2));

--      if rising_edge(clk) then

--         if write_enable = '1' then

--            dual_port_ram1(conv_integer(addr_b)) := reg_dest_new;

--            dual_port_ram2(conv_integer(addr_b)) := reg_dest_new;

--         end if;

--      end if;

--   end process;

   -- Option #3

   -- Generic Two-Port Synchronous RAM

   -- generic_tpram can be obtained from:

   -- http://www.opencores.org/cvsweb.shtml/generic_memories/

   -- Supports ASICs (Artisan, Avant, and Virage) and Xilinx FPGA

--   bank1 : generic_tpram port map (

--      clk_a  => clk,

--      rst_a  => '0',

--      ce_a   => '1',

--      we_a   => '0',

--      oe_a   => '1',

--      addr_a => addr_a1,

--      di_a   => ZERO,

--      do_a   => data_out1,

--

--      clk_b  => clk,

--      rst_b  => '0',

--      ce_b   => '1',

--      we_b   => write_enable,

--      oe_b   => '0',

--      addr_b => addr_b,

--      di_a   => reg_dest_new);

--

--   bank2 : generic_tpram port map (

--      clk_a  => clk,

--      rst_a  => '0',

--      ce_a   => '1',

--      we_a   => '0',

--      oe_a   => '1',

--      addr_a => addr_a2,

--      di_a   => ZERO,

--      do_a   => data_out2,

--

--      clk_b  => clk,

--      rst_b  => '0',

--      ce_b   => '1',

--      we_b   => write_enable,

--      oe_b   => '0',

--      addr_b => addr_b,

--      di_a   => reg_dest_new);

   -- Option #4

   -- Xilinx mode using four 16x16 banks

--   bank1_high: ramb4_s16_s16 port map (

--      clka  => clk,

--      rsta  => sig_false,

--      addra => addr_a1,

--      dia   => ZERO(31 downto 16),

--      ena   => sig_true,

--      wea   => sig_false,

--      doa   => data_out1(31 downto 16),

--

--      clkb  => clk,

--      rstb  => sig_false,

--      addrb => addr_b,

--      dib   => reg_dest_new(31 downto 16),

--      enb   => sig_true,

--      web   => write_enable);

--

--   bank1_low: ramb4_s16_s16 port map (

--      clka  => clk,

--      rsta  => sig_false,

--      addra => addr_a1,

--      dia   => ZERO(15 downto 0),

--      ena   => sig_true,

--      wea   => sig_false,

--      doa   => data_out1(15 downto 0),

--

--      clkb  => clk,

--      rstb  => sig_false,

--      addrb => addr_b,

--      dib   => reg_dest_new(15 downto 0),

--      enb   => sig_true,

--      web   => write_enable);

--

--   bank2_high: ramb4_s16_s16 port map (

--      clka  => clk,

--      rsta  => sig_false,

--      addra => addr_a2,

--      dia   => ZERO(31 downto 16),

--      ena   => sig_true,

--      wea   => sig_false,

--      doa   => data_out2(31 downto 16),

--

--      clkb  => clk,

--      rstb  => sig_false,

--      addrb => addr_b,

--      dib   => reg_dest_new(31 downto 16),

--      enb   => sig_true,

--      web   => write_enable);

--

--   bank2_low: ramb4_s16_s16 port map (

--      clka  => clk,

--      rsta  => sig_false,

--      addra => addr_a2,

--      dia   => ZERO(15 downto 0),

--      ena   => sig_true,

--      wea   => sig_false,

--      doa   => data_out2(15 downto 0),

--

--      clkb  => clk,

--      rstb  => sig_false,

--      addrb => addr_b,

--      dib   => reg_dest_new(15 downto 0),

--      enb   => sig_true,

--      web   => write_enable);

   -- Option #5

   -- Altera LPM_RAM_DP

--   bank1: LPM_RAM_DP 

--      generic map (

--      LPM_WIDTH    => 32,

--      LPM_WIDTHAD  => 5,

--      LPM_NUMWORDS => 32,

--??      LPM_INDATA   => "UNREGISTERED",

--??      LPM_OUTDATA  => "UNREGISTERED",

--??      LPM_RDADDRESS_CONTROL => "UNREGISTERED",

--??      LPM_WRADDRESS_CONTROL => "UNREGISTERED"

--   )

--   port map (RDCLOCK => clk,

--      RDADDRESS => addr_a1,

--      DATA      => reg_dest_new,

--      WRADDRESS => addr_b,

--      WREN      => write_enable,

--      WRCLOCK   => clk,

--      Q         => data_out1);

--

--   bank2: LPM_RAM_DP 

--      generic map (

--      LPM_WIDTH    => 32,

--      LPM_WIDTHAD  => 5,

--      LPM_NUMWORDS => 32,

--??      LPM_INDATA   => "UNREGISTERED",

--??      LPM_OUTDATA  => "UNREGISTERED",

--??      LPM_RDADDRESS_CONTROL => "UNREGISTERED",

--??      LPM_WRADDRESS_CONTROL => "UNREGISTERED"

--   )

--   port map (RDCLOCK => clk,

--      RDADDRESS => addr_a2,

--      DATA      => reg_dest_new,

--      WRADDRESS => addr_b,

--      WREN      => write_enable,

--      WRCLOCK   => clk,

--      Q         => data_out2);

end; --architecture ram_block