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

-- TITLE: DDR SDRAM Interface

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

-- DATE CREATED: 7/26/07

-- FILENAME: ddr_ctrl.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:

--    Double Data Rate Sychronous Dynamic Random Access Memory Interface

--    ROW = address(25 downto 13)

--    BANK = address(12 downto 11)

--    COL = address(10 downto 2)

--    Requires CAS latency=2; burst size=2.  

--    Requires clk changes on rising_edge(clk_2x).

--    Requires active, address, byte_we, data_w stable throughout transfer.

--    DLL mode requires 77MHz.  Non-DLL mode runs at 25 MHz.

--

-- cycle_cnt 777777770000111122223333444455556666777777777777

-- clk_2x    --__--__--__--__--__--__--__--__--__--__--__--__

-- clk       ____----____----____----____----____----____----

-- SD_CLK    ----____----____----____----____----____----____

-- cmd       ____write+++WRITE+++____________________________

-- SD_DQ     ~~~~~~~~~~~~~~uuuullllUUUULLLL~~~~~~~~~~~~~~~~~~

--

-- cycle_cnt 777777770000111122223333444455556666777777777777

-- clk_2x    --__--__--__--__--__--__--__--__--__--__--__--__

-- clk       ____----____----____----____----____----____----

-- SD_CLK    ----____----____----____----____----____----____

-- cmd       ____read++++________________________read++++____

-- SD_DQ     ~~~~~~~~~~~~~~~~~~~~~~~~uuuullll~~~~~~~~~~~~~~~~

-- SD_DQnDLL ~~~~~~~~~~~~~~~~~~~~~~~~~~uuuullll~~~~~~~~~~~~~~

-- pause     ____------------------------________------------

--

-- Must run DdrInit() to initialize DDR chip.

-- Read Micron DDR SDRAM MT46V32M16 data sheet for more details.

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

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

use ieee.std_logic_arith.all;

use work.mlite_pack.all;

entity ddr_ctrl is

   port(

      clk      : in std_logic;

      clk_2x   : in std_logic;

      reset_in : in std_logic;

      address  : in std_logic_vector(25 downto 2);

      byte_we  : in std_logic_vector(3 downto 0);

      data_w   : in std_logic_vector(31 downto 0);

      data_r   : out std_logic_vector(31 downto 0);

      active   : in std_logic;

      pause    : out std_logic;

      SD_CK_P  : out std_logic;     --clock_positive

      SD_CK_N  : out std_logic;     --clock_negative

      SD_CKE   : out std_logic;     --clock_enable

      SD_BA    : out std_logic_vector(1 downto 0);  --bank_address

      SD_A     : out std_logic_vector(12 downto 0); --address(row or col)

      SD_CS    : out std_logic;     --chip_select

      SD_RAS   : out std_logic;     --row_address_strobe

      SD_CAS   : out std_logic;     --column_address_strobe

      SD_WE    : out std_logic;     --write_enable

      SD_DQ    : inout std_logic_vector(15 downto 0); --data

      SD_UDM   : out std_logic;     --upper_byte_enable

      SD_UDQS  : inout std_logic;   --upper_data_strobe

      SD_LDM   : out std_logic;     --low_byte_enable

      SD_LDQS  : inout std_logic);  --low_data_strobe

end; --entity ddr

architecture logic of ddr_ctrl is

   --Commands for bits RAS & CAS & WE

   subtype command_type is std_logic_vector(2 downto 0);

   constant COMMAND_LMR          : command_type := "000";

   constant COMMAND_AUTO_REFRESH : command_type := "001";

   constant COMMAND_PRECHARGE    : command_type := "010";

   constant COMMAND_ACTIVE       : command_type := "011";

   constant COMMAND_WRITE        : command_type := "100";

   constant COMMAND_READ         : command_type := "101";

   constant COMMAND_TERMINATE    : command_type := "110";

   constant COMMAND_NOP          : command_type := "111";

   subtype ddr_state_type is std_logic_vector(3 downto 0);

   constant STATE_POWER_ON     : ddr_state_type := "0000";

   constant STATE_IDLE         : ddr_state_type := "0001";

   constant STATE_ROW_ACTIVATE : ddr_state_type := "0010";

   constant STATE_ROW_ACTIVE   : ddr_state_type := "0011";

   constant STATE_READ         : ddr_state_type := "0100";

   constant STATE_READ2        : ddr_state_type := "0101";

   constant STATE_READ3        : ddr_state_type := "0110";

   constant STATE_PRECHARGE    : ddr_state_type := "0111";

   constant STATE_PRECHARGE2   : ddr_state_type := "1000";

   signal state_prev   : ddr_state_type;

   signal refresh_cnt  : std_logic_vector(7 downto 0);

   signal data_write2  : std_logic_vector(47 downto 0); --write pipeline

   signal byte_we_reg2 : std_logic_vector(5 downto 0);  --write pipeline

   signal write_active : std_logic;

   signal write_prev   : std_logic;

   signal cycle_count  : std_logic_vector(2 downto 0);  --half clocks since op

   signal cycle_count2 : std_logic_vector(2 downto 0);  --delayed by quarter clock

   signal cke_reg      : std_logic;

   signal clk_p        : std_logic;

   signal bank_open    : std_logic_vector(3 downto 0);

   signal data_read    : std_logic_vector(31 downto 0);

begin

   ddr_proc: process(clk, clk_p, clk_2x, reset_in,

                     address, byte_we, data_w, active,

                     SD_DQ, SD_UDQS, SD_LDQS,

                     state_prev, refresh_cnt,

                     byte_we_reg2, data_write2,

                     cycle_count, cycle_count2, write_prev,

                     write_active, cke_reg, bank_open,

                     data_read)

   type address_array_type is array(3 downto 0) of std_logic_vector(12 downto 0);

   variable address_row    : address_array_type;

   variable command        : std_logic_vector(2 downto 0); --RAS & CAS & WE

   variable bank_index     : integer;

   variable state_current  : ddr_state_type;

   begin

      command := COMMAND_NOP;

      bank_index := conv_integer(address(12 downto 11));

      state_current := state_prev;

      --DDR state machine to determine state_current and command

      case state_prev is

         when STATE_POWER_ON =>

            if active = '1' then

               if byte_we /= "0000" then

                  command := address(6 downto 4); --LMR="000"

               else

                  state_current := STATE_IDLE;  --read transistions to STATE_IDLE

               end if;

            end if;

         when STATE_IDLE =>

            if refresh_cnt(7) = '1' then

               state_current := STATE_PRECHARGE;

               command := COMMAND_AUTO_REFRESH;

            elsif active = '1' then

               state_current := STATE_ROW_ACTIVATE;

               command := COMMAND_ACTIVE;

            end if;

         when STATE_ROW_ACTIVATE =>

            state_current := STATE_ROW_ACTIVE;

         when STATE_ROW_ACTIVE =>

            if refresh_cnt(7) = '1' then

               if write_prev = '0' then

                  state_current := STATE_PRECHARGE;

                  command := COMMAND_PRECHARGE;

               end if;

            elsif active = '1' then

               if bank_open(bank_index) = '0' then

                  state_current := STATE_ROW_ACTIVATE;

                  command := COMMAND_ACTIVE;

               elsif address(25 downto 13) /= address_row(bank_index) then

                  if write_prev = '0' then

                     state_current := STATE_PRECHARGE;

                     command := COMMAND_PRECHARGE;

                  end if;

               else

                  if byte_we /= "0000" then

                     command := COMMAND_WRITE;

                  elsif write_prev = '0' then

                     state_current := STATE_READ;

                     command := COMMAND_READ;

                  end if;

               end if;

            end if;

         when STATE_READ =>

            state_current := STATE_READ2;

         when STATE_READ2 =>

            state_current := STATE_READ3;

         when STATE_READ3 =>

            state_current := STATE_ROW_ACTIVE;

         when STATE_PRECHARGE =>

            state_current := STATE_PRECHARGE2;

         when STATE_PRECHARGE2 =>

            state_current := STATE_IDLE;

         when others =>

            state_current := STATE_IDLE;

      end case; --state_prev

      --rising_edge(clk) domain registers

      if reset_in = '1' then

         state_prev   <= STATE_POWER_ON;

         cke_reg      <= '0';

         refresh_cnt  <= ZERO(7 downto 0);

         write_prev   <= '0';

         write_active <= '0';

         bank_open    <= "0000";

      elsif rising_edge(clk) then

         if active = '1' then

            cke_reg <= '1';

         end if;

         if command = COMMAND_WRITE then

            write_prev <= '1';

         elsif cycle_count2(2 downto 1) = "11" then

            write_prev <= '0';

         end if;

         if command = COMMAND_WRITE then

            write_active <= '1';

         elsif cycle_count2 = "100" then

            write_active <= '0';

         end if;

         if command = COMMAND_ACTIVE then

            bank_open(bank_index) <= '1';

            address_row(bank_index) := address(25 downto 13);

         end if;

         if command = COMMAND_PRECHARGE then

            bank_open <= "0000";

         end if;

         if command = COMMAND_AUTO_REFRESH then

            refresh_cnt <= ZERO(7 downto 0);

         else

            refresh_cnt <= refresh_cnt + 1;

         end if;

         state_prev <= state_current;

      end if; --rising_edge(clk)

      --rising_edge(clk_2x) domain registers

      if reset_in = '1' then

         cycle_count <= "000";

      elsif rising_edge(clk_2x) then

         --Cycle_count

         if (command = COMMAND_READ or command = COMMAND_WRITE) and clk = '1' then

            cycle_count <= "000";

         elsif cycle_count /= "111" then

            cycle_count <= cycle_count + 1;

         end if;

         clk_p <= clk;  --earlier version of not clk         

         --Read data (DLL disabled)

         if cycle_count = "100" then

            data_read(31 downto 16) <= SD_DQ; --data

         elsif cycle_count = "101" then

            data_read(15 downto 0) <= SD_DQ;

         end if;

      end if;

      --falling_edge(clk_2x) domain registers

      if reset_in = '1' then

         cycle_count2 <= "000";

         data_write2 <= ZERO(15 downto 0) & ZERO;

         byte_we_reg2 <= "000000";

      elsif falling_edge(clk_2x) then

         cycle_count2 <= cycle_count;

         --Write pipeline

         if clk = '0' then

            data_write2 <= data_write2(31 downto 16) & data_w;

            byte_we_reg2 <= byte_we_reg2(3 downto 2) & byte_we;

         else

            data_write2(47 downto 16) <= data_write2(31 downto 0);

            byte_we_reg2(5 downto 2) <= byte_we_reg2(3 downto 0);

         end if;

         --Read data (DLL enabled)

         --if cycle_count = "100" then

         --   data_read(31 downto 16) <= SD_DQ; --data

         --elsif cycle_count = "101" then

         --   data_read(15 downto 0) <= SD_DQ;

         --end if;

      end if;

      data_r <= data_read;

      --Write data

      if write_active = '1' then

         SD_UDQS <= clk_p;                   --upper_data_strobe 

         SD_LDQS <= clk_p;                   --low_data_strobe

         SD_DQ <= data_write2(47 downto 32); --data

         SD_UDM <= not byte_we_reg2(5);      --upper_byte_enable

         SD_LDM <= not byte_we_reg2(4);      --low_byte_enable

      else

         SD_UDQS <= 'Z';               --upper_data_strobe 

         SD_LDQS <= 'Z';               --low_data_strobe

         SD_DQ <= "ZZZZZZZZZZZZZZZZ";  --data

         SD_UDM <= 'Z';

         SD_LDM <= 'Z';

      end if;

      --DDR control signals

      SD_CK_P <= clk_p;                --clock_positive

      SD_CK_N <= not clk_p;            --clock_negative

      SD_CKE  <= cke_reg;              --clock_enable

      SD_BA   <= address(12 downto 11);  --bank_address

      if command = COMMAND_ACTIVE or state_current = STATE_POWER_ON then

         SD_A <= address(25 downto 13);  --address row

      elsif command = COMMAND_READ or command = COMMAND_WRITE then

         SD_A <= "000" & address(10 downto 2) & "0"; --address col

      else

         SD_A <= "0010000000000";      --PERCHARGE all banks

      end if;

      SD_CS   <= not cke_reg;          --chip_select

      SD_RAS  <= command(2);           --row_address_strobe

      SD_CAS  <= command(1);           --column_address_strobe

      SD_WE   <= command(0);           --write_enable

      if active = '1' and state_current /= STATE_POWER_ON and

         command /= COMMAND_WRITE and state_prev /= STATE_READ3 then

         pause <= '1';

      else

         pause <= '0';

      end if;

   end process; --ddr_proc

end; --architecture logic