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

-- TITLE: Register Bank

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

-- DATE CREATED: 2/2/01

-- FILENAME: reg_bank.vhd

-- PROJECT: Plasma 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.mlite_pack.all;

entity reg_bank is

   generic(memory_type : string := "XILINX_16X");

   port(clk            : in  std_logic;

        reset_in       : in  std_logic;

        pause          : 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 intr_enable_reg : 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_read1, addr_read2 : std_logic_vector(4 downto 0);

   signal addr_write             : 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,

      intr_enable_reg, data_out1, data_out2, reset_in, pause)

begin

   --setup for first dual-port memory

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

      addr_read1 <= "00000";

   else

      addr_read1 <= 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) & intr_enable_reg;

                    --interrupt vector address = 0x3c

   when "111111" => reg_source_out <= ZERO(31 downto 8) & "00111100";

   when others   => reg_source_out <= data_out1;

   end case;

   --setup for second dual-port memory

   addr_read2 <= 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 write port for both dual-port memories

   if rd_index /= "000000" and rd_index /= "101100" and pause = '0' then

      write_enable <= '1';

   else

      write_enable <= '0';

   end if;

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

      addr_write <= "00000";

   else

      addr_write <= rd_index(4 downto 0);

   end if;

   if reset_in = '1' then

      intr_enable_reg <= '0';

   elsif rising_edge(clk) then

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

         intr_enable_reg <= '0';      --disable interrupts

      elsif rd_index = "101100" then

         intr_enable_reg <= reg_dest_new(0);

      end if;

   end if;

   intr_enable <= intr_enable_reg;

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

   tri_port_mem:

   if memory_type = "TRI_PORT_X" generate

      ram_proc: process(clk, addr_read1, addr_read2,

            addr_write, reg_dest_new, write_enable)

      variable tri_port_ram : ram_type := (others => ZERO);

      begin

         data_out1 <= tri_port_ram(conv_integer(addr_read1));

         data_out2 <= tri_port_ram(conv_integer(addr_read2));

         if rising_edge(clk) then

            if write_enable = '1' then

               tri_port_ram(conv_integer(addr_write)) := reg_dest_new;

            end if;

         end if;

      end process;

   end generate; --tri_port_mem

   -- Option #2

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

   dual_port_mem:

   if memory_type = "DUAL_PORT_" generate

      ram_proc2: process(clk, addr_read1, addr_read2,

            addr_write, reg_dest_new, write_enable)

      variable dual_port_ram1 : ram_type := (others => ZERO);

      variable dual_port_ram2 : ram_type := (others => ZERO);

      begin

         data_out1 <= dual_port_ram1(conv_integer(addr_read1));

         data_out2 <= dual_port_ram2(conv_integer(addr_read2));

         if rising_edge(clk) then

            if write_enable = '1' then

               dual_port_ram1(conv_integer(addr_write)) := reg_dest_new;

               dual_port_ram2(conv_integer(addr_write)) := reg_dest_new;

            end if;

         end if;

      end process;

   end generate; --dual_port_mem

   -- Option #3

   -- RAM16X1D: 16 x 1 positive edge write, asynchronous read dual-port 

   -- distributed RAM for all Xilinx FPGAs

   -- From library UNISIM; use UNISIM.vcomponents.all;

   xilinx_16x1d:

   if memory_type = "XILINX_16X" generate

      signal data_out1A, data_out1B : std_logic_vector(31 downto 0);

      signal data_out2A, data_out2B : std_logic_vector(31 downto 0);

      signal weA, weB               : std_logic;

      signal no_connect             : std_logic_vector(127 downto 0);

   begin

      weA <= write_enable and not addr_write(4);  --lower 16 registers

      weB <= write_enable and addr_write(4);      --upper 16 registers

      reg_loop: for i in 0 to 31 generate

      begin

         --Read port 1 lower 16 registers

         reg_bit1a : RAM16X1D

         port map (

            WCLK  => clk,              -- Port A write clock input

            WE    => weA,              -- Port A write enable input

            A0    => addr_write(0),    -- Port A address[0] input bit

            A1    => addr_write(1),    -- Port A address[1] input bit

            A2    => addr_write(2),    -- Port A address[2] input bit

            A3    => addr_write(3),    -- Port A address[3] input bit

            D     => reg_dest_new(i),  -- Port A 1-bit data input

            DPRA0 => addr_read1(0),    -- Port B address[0] input bit

            DPRA1 => addr_read1(1),    -- Port B address[1] input bit

            DPRA2 => addr_read1(2),    -- Port B address[2] input bit

            DPRA3 => addr_read1(3),    -- Port B address[3] input bit

            DPO   => data_out1A(i),    -- Port B 1-bit data output

            SPO   => no_connect(i)     -- Port A 1-bit data output

         );

         --Read port 1 upper 16 registers

         reg_bit1b : RAM16X1D

         port map (

            WCLK  => clk,              -- Port A write clock input

            WE    => weB,              -- Port A write enable input

            A0    => addr_write(0),    -- Port A address[0] input bit

            A1    => addr_write(1),    -- Port A address[1] input bit

            A2    => addr_write(2),    -- Port A address[2] input bit

            A3    => addr_write(3),    -- Port A address[3] input bit

            D     => reg_dest_new(i),  -- Port A 1-bit data input

            DPRA0 => addr_read1(0),    -- Port B address[0] input bit

            DPRA1 => addr_read1(1),    -- Port B address[1] input bit

            DPRA2 => addr_read1(2),    -- Port B address[2] input bit

            DPRA3 => addr_read1(3),    -- Port B address[3] input bit

            DPO   => data_out1B(i),    -- Port B 1-bit data output

            SPO   => no_connect(32+i)  -- Port A 1-bit data output

         );

         --Read port 2 lower 16 registers

         reg_bit2a : RAM16X1D

         port map (

            WCLK  => clk,              -- Port A write clock input

            WE    => weA,              -- Port A write enable input

            A0    => addr_write(0),    -- Port A address[0] input bit

            A1    => addr_write(1),    -- Port A address[1] input bit

            A2    => addr_write(2),    -- Port A address[2] input bit

            A3    => addr_write(3),    -- Port A address[3] input bit

            D     => reg_dest_new(i),  -- Port A 1-bit data input

            DPRA0 => addr_read2(0),    -- Port B address[0] input bit

            DPRA1 => addr_read2(1),    -- Port B address[1] input bit

            DPRA2 => addr_read2(2),    -- Port B address[2] input bit

            DPRA3 => addr_read2(3),    -- Port B address[3] input bit

            DPO   => data_out2A(i),    -- Port B 1-bit data output

            SPO   => no_connect(64+i)  -- Port A 1-bit data output

         );

         --Read port 2 upper 16 registers

         reg_bit2b : RAM16X1D

         port map (

            WCLK  => clk,              -- Port A write clock input

            WE    => weB,              -- Port A write enable input

            A0    => addr_write(0),    -- Port A address[0] input bit

            A1    => addr_write(1),    -- Port A address[1] input bit

            A2    => addr_write(2),    -- Port A address[2] input bit

            A3    => addr_write(3),    -- Port A address[3] input bit

            D     => reg_dest_new(i),  -- Port A 1-bit data input

            DPRA0 => addr_read2(0),    -- Port B address[0] input bit

            DPRA1 => addr_read2(1),    -- Port B address[1] input bit

            DPRA2 => addr_read2(2),    -- Port B address[2] input bit

            DPRA3 => addr_read2(3),    -- Port B address[3] input bit

            DPO   => data_out2B(i),    -- Port B 1-bit data output

            SPO   => no_connect(96+i)  -- Port A 1-bit data output

         );

      end generate; --reg_loop

      data_out1 <= data_out1A when addr_read1(4)='0' else data_out1B;

      data_out2 <= data_out2A when addr_read2(4)='0' else data_out2B;

   end generate; --xilinx_16x1d

   -- Option #4

   -- Altera LPM_RAM_DP

   altera_mem:

   if memory_type = "ALTERA_LPM" generate

      signal clk_delayed : std_logic;

      signal addr_reg    : std_logic_vector(4 downto 0);

      signal data_reg    : std_logic_vector(31 downto 0);

      signal q1          : std_logic_vector(31 downto 0);

      signal q2          : std_logic_vector(31 downto 0);

   begin

      -- Altera dual port RAMs must have the addresses registered (sampled

      -- at the rising edge).  This is very unfortunate.

      -- Therefore, the dual port RAM read clock must delayed so that

      -- the read address signal can be sent from the mem_ctrl block.

      -- This solution also delays the how fast the registers are read so the 

      -- maximum clock speed is cut in half (12.5 MHz instead of 25 MHz).

      clk_delayed <= not clk;  --Could be delayed by 1/4 clock cycle instead

      dpram_bypass: process(clk, addr_write, reg_dest_new)

      begin

         if rising_edge(clk) and write_enable = '1' then

            addr_reg <= addr_write;

            data_reg <= reg_dest_new;

         end if;

      end process; --dpram_bypass

      -- Bypass dpram if reading what was just written (Altera limitation)

      data_out1 <= q1 when addr_read1 /= addr_reg else data_reg;

      data_out2 <= q2 when addr_read2 /= addr_reg else data_reg;

      lpm_ram_dp_component1 : lpm_ram_dp

      generic map (

         LPM_WIDTH => 32,

         LPM_WIDTHAD => 5,

         --LPM_NUMWORDS => 0,

         LPM_INDATA => "REGISTERED",

         LPM_OUTDATA => "UNREGISTERED",

         LPM_RDADDRESS_CONTROL => "REGISTERED",

         LPM_WRADDRESS_CONTROL => "REGISTERED",

         LPM_FILE => "UNUSED",

         LPM_TYPE => "LPM_RAM_DP",

         USE_EAB  => "ON",

         INTENDED_DEVICE_FAMILY => "UNUSED",

         RDEN_USED => "FALSE",

         LPM_HINT => "UNUSED")

      port map (

         RDCLOCK   => clk_delayed,

         RDCLKEN   => '1',

         RDADDRESS => addr_read1,

         RDEN      => '1',

         DATA      => reg_dest_new,

         WRADDRESS => addr_write,

         WREN      => write_enable,

         WRCLOCK   => clk,

         WRCLKEN   => '1',

         Q         => q1);

      lpm_ram_dp_component2 : lpm_ram_dp

      generic map (

         LPM_WIDTH => 32,

         LPM_WIDTHAD => 5,

         --LPM_NUMWORDS => 0,

         LPM_INDATA => "REGISTERED",

         LPM_OUTDATA => "UNREGISTERED",

         LPM_RDADDRESS_CONTROL => "REGISTERED",

         LPM_WRADDRESS_CONTROL => "REGISTERED",

         LPM_FILE => "UNUSED",

         LPM_TYPE => "LPM_RAM_DP",

         USE_EAB  => "ON",

         INTENDED_DEVICE_FAMILY => "UNUSED",

         RDEN_USED => "FALSE",

         LPM_HINT => "UNUSED")

      port map (

         RDCLOCK   => clk_delayed,

         RDCLKEN   => '1',

         RDADDRESS => addr_read2,

         RDEN      => '1',

         DATA      => reg_dest_new,

         WRADDRESS => addr_write,

         WREN      => write_enable,

         WRCLOCK   => clk,

         WRCLKEN   => '1',

         Q         => q2);

   end generate; --altera_mem

end; --architecture ram_block