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---

---  Gigabit Ethernet MAC

---

---  :Author: Jonathan P Dawson

---  :Date: 17/10/2013

---  :email: chips@jondawson.org.uk

---  :license: MIT

---  :Copyright: Copyright (C) Jonathan P Dawson 2013

---

---  A gigabit ethernet MAC

---

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

---

---Gigabit Ethernet

---================

---

---Send and receive Ethernet packets. Using a Ethernet Physical Interface.

---

---Features:

---

---+ Supports 1Gbit/s ethernet only via a gmii interface.

---+ Supports full duplex mode only.

---

---Interface

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

---:input: TX - Data to send (16 bits).

---:output: RX - Data to send (16 bits).

---

---Ethernet Packet Structure

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

---

---+-------------+-------------+--------+--------+---------+---------+-----+

---| Description | destination | source | length | payload | padding | FSC |

---+=============+=============+========+========+=========+=========+=====+

---|    Bytes    |      6      |   6    |    2   |  0-1500 |   0-46  |  4  |

---+-------------+-------------+--------+--------+---------+---------+-----+

---

---Notes:

---

---+ The *length* field is the length of the ethernet payload.

---+ The *Ethernet Output* block will automatically append the FSC to 

---  outgoing packets.

---+ The *FSC* of incoming packets will be checked, and bad packets will

---  be discarded. The *FSC* will be stripped from incoming packets.

---+ The length of the *payload* + *padding* must be 46-1500 bytes.

---+ Incoming packets of incorrect *length* will be discarded.

---

---Usage

--------

---

---Transmit

---~~~~~~~~

---The first 16 bit word on the TX input is interpreted as the length of the

---packet in bytes (including the MAC address, length and payload, but not the 

---preamble or FSC). Subsequent words on the TX input are interpreted as the

---content of the packet. If length is an odd number of bytes, then the least

---significant byte of the last word will be ignored.

---The FSC will be appended for you, but you need to supply the destination,

---source and length fields.

---

---Receive

---~~~~~~~~

---The first 16 bit word on the RX output will be the length of the packet in 

---bytes (including the MAC address, length and payload, but not the 

---preamble or FSC). Subsequent words on the RX output will be the

---content of the packet. If length is an odd number of bytes, then the least

---significant byte of the last word will not contain usefull data.

---The FSC will be stripped from incoming packets, but the destination,

---source and length fields will be included.

---

---Hardware details

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

---This component used two clocks, the local clock used to transfer data

---between components, and a 125MHz clock source for sending data to the

---Ethernet physical interface. This clock is also forwarded along with the

---data to the ethernet phy.

---

library ieee;

use ieee.numeric_std.all;

use ieee.std_logic_1164.all;

entity gigabit_ethernet is

  port(

    CLK         : in  std_logic;

    RST         : in  std_logic;

    --Ethernet Clock

    CLK_125_MHZ : in  std_logic;

    --GMII IF

    GTXCLK      : out std_logic;

    TXCLK       : in  std_logic;

    TXER        : out std_logic;

    TXEN        : out std_logic;

    TXD         : out std_logic_vector(7 downto 0);

    PHY_RESET   : out std_logic;

    RXCLK       : in  std_logic;

    RXER        : in  std_logic;

    RXDV        : in  std_logic;

    RXD         : in  std_logic_vector(7 downto 0);

    --RX STREAM

    TX          : in  std_logic_vector(15 downto 0);

    TX_STB      : in  std_logic;

    TX_ACK      : out std_logic;

    --RX STREAM

    RX          : out std_logic_vector(15 downto 0);

    RX_STB      : out std_logic;

    RX_ACK      : in  std_logic

  );

end entity gigabit_ethernet;

architecture RTL of gigabit_ethernet is

  -- polynomial: (0 1 2 4 5 7 8 10 11 12 16 22 23 26 32)

  -- data width: 8

  -- convention: the first serial bit is D[0]

  function NEXTCRC32_D8

    (DATA: std_logic_vector(7 downto 0);

    CRC:  std_logic_vector(31 downto 0))

    return std_logic_vector is

    variable D:      std_logic_vector(7 downto 0);

    variable C:      std_logic_vector(31 downto 0);

    variable NEWCRC: std_logic_vector(31 downto 0);

  begin

    D := DATA;

    C := CRC;

    NewCRC(0):=C(24) xor C(30) xor D(1) xor D(7);

    NewCRC(1):=C(25) xor C(31) xor D(0) xor D(6) xor C(24) xor C(30) xor D(1)

               xor D(7);

    NewCRC(2):=C(26) xor D(5) xor C(25) xor C(31) xor D(0) xor D(6) xor C(24)

               xor C(30) xor D(1) xor D(7);

    NewCRC(3):=C(27) xor D(4) xor C(26) xor D(5) xor C(25) xor C(31) xor D(0)

               xor D(6);

    NewCRC(4):=C(28) xor D(3) xor C(27) xor D(4) xor C(26) xor D(5) xor C(24)

              xor C(30) xor D(1) xor D(7);

    NewCRC(5):=C(29) xor D(2) xor C(28) xor D(3) xor C(27) xor D(4) xor C(25)

              xor C(31) xor D(0) xor D(6) xor C(24) xor C(30) xor D(1) xor D(7);

    NewCRC(6):=C(30) xor D(1) xor C(29) xor D(2) xor C(28) xor D(3) xor C(26)

              xor D(5) xor C(25) xor C(31) xor D(0) xor D(6);

    NewCRC(7):=C(31) xor D(0) xor C(29) xor D(2) xor C(27) xor D(4) xor C(26)

              xor D(5) xor C(24) xor D(7);

    NewCRC(8):=C(0) xor C(28) xor D(3) xor C(27) xor D(4) xor C(25) xor D(6)

              xor C(24) xor D(7);

    NewCRC(9):=C(1) xor C(29) xor D(2) xor C(28) xor D(3) xor C(26) xor D(5)

              xor C(25) xor D(6);

    NewCRC(10):=C(2) xor C(29) xor D(2) xor C(27) xor D(4) xor C(26) xor D(5)

              xor C(24) xor D(7);

    NewCRC(11):=C(3) xor C(28) xor D(3) xor C(27) xor D(4) xor C(25) xor D(6)

              xor C(24) xor D(7);

    NewCRC(12):=C(4) xor C(29) xor D(2) xor C(28) xor D(3) xor C(26) xor D(5)

              xor C(25) xor D(6) xor C(24) xor C(30) xor D(1) xor D(7);

    NewCRC(13):=C(5) xor C(30) xor D(1) xor C(29) xor D(2) xor C(27) xor D(4)

              xor C(26) xor D(5) xor C(25) xor C(31) xor D(0) xor D(6);

    NewCRC(14):=C(6) xor C(31) xor D(0) xor C(30) xor D(1) xor C(28) xor D(3)

              xor C(27) xor D(4) xor C(26) xor D(5);

    NewCRC(15):=C(7) xor C(31) xor D(0) xor C(29) xor D(2) xor C(28) xor D(3)

              xor C(27) xor D(4);

    NewCRC(16):=C(8) xor C(29) xor D(2) xor C(28) xor D(3) xor C(24) xor D(7);

    NewCRC(17):=C(9) xor C(30) xor D(1) xor C(29) xor D(2) xor C(25) xor D(6);

    NewCRC(18):=C(10) xor C(31) xor D(0) xor C(30) xor D(1) xor C(26) xor D(5);

    NewCRC(19):=C(11) xor C(31) xor D(0) xor C(27) xor D(4);

    NewCRC(20):=C(12) xor C(28) xor D(3);

    NewCRC(21):=C(13) xor C(29) xor D(2);

    NewCRC(22):=C(14) xor C(24) xor D(7);

    NewCRC(23):=C(15) xor C(25) xor D(6) xor C(24) xor C(30) xor D(1) xor D(7);

    NewCRC(24):=C(16) xor C(26) xor D(5) xor C(25) xor C(31) xor D(0) xor D(6);

    NewCRC(25):=C(17) xor C(27) xor D(4) xor C(26) xor D(5);

    NewCRC(26):=C(18) xor C(28) xor D(3) xor C(27) xor D(4) xor C(24) xor C(30)

              xor D(1) xor D(7);

    NewCRC(27):=C(19) xor C(29) xor D(2) xor C(28) xor D(3) xor C(25) xor C(31)

              xor D(0) xor D(6);

    NewCRC(28):=C(20) xor C(30) xor D(1) xor C(29) xor D(2) xor C(26) xor D(5);

    NewCRC(29):=C(21) xor C(31) xor D(0) xor C(30) xor D(1) xor C(27) xor D(4);

    NewCRC(30):=C(22) xor C(31) xor D(0) xor C(28) xor D(3);

    NewCRC(31):=C(23) xor C(29) xor D(2);

    return NEWCRC;

  end NEXTCRC32_D8;

  -- Reverse the input vector.

  function REVERSED(slv: std_logic_vector) return std_logic_vector is

     variable result: std_logic_vector(slv'reverse_range);

  begin

     for i in slv'range loop

       result(i) := slv(i);

     end loop;

     return result;

  end REVERSED;

  --constants

  constant ADDRESS_BITS : integer := 11;

  constant ADDRESS_MAX : integer := (2**ADDRESS_BITS) - 1;

  --memories

  type TX_MEMORY_TYPE is array (0 to 511) of

    std_logic_vector(15 downto 0);

  shared variable TX_MEMORY : TX_MEMORY_TYPE;

  type RX_MEMORY_TYPE is array (0 to ADDRESS_MAX) of

    std_logic_vector(15 downto 0);

  shared variable RX_MEMORY : RX_MEMORY_TYPE;

  type ADDRESS_ARRAY is array (0 to 31) of

    unsigned(ADDRESS_BITS - 1 downto 0);

  --state variables

  type TX_PHY_STATE_TYPE is (WAIT_NEW_PACKET, PREAMBLE_0, PREAMBLE_1,

    PREAMBLE_2, PREAMBLE_3, PREAMBLE_4, PREAMBLE_5, PREAMBLE_6, SFD,

    SEND_DATA_HI, SEND_DATA_LO, SEND_CRC_3, SEND_CRC_2, SEND_CRC_1,

    SEND_CRC_0, DONE_STATE);

  signal TX_PHY_STATE : TX_PHY_STATE_TYPE;

  type TX_PACKET_STATE_TYPE is(GET_LENGTH, GET_DATA, SEND_PACKET,

    WAIT_NOT_DONE);

  signal TX_PACKET_STATE : TX_PACKET_STATE_TYPE;

  type RX_PHY_STATE_TYPE is (WAIT_START, PREAMBLE, DATA_HIGH, DATA_LOW,

    END_OF_FRAME, NOTIFY_NEW_PACKET);

  signal RX_PHY_STATE : RX_PHY_STATE_TYPE;

  type RX_PACKET_STATE_TYPE is (WAIT_INITIALISE, WAIT_NEW_PACKET,

    SEND_DATA, PREFETCH0, PREFETCH1, SEND_LENGTH);

  signal RX_PACKET_STATE : RX_PACKET_STATE_TYPE;

  --TX signals

  signal TX_WRITE                  : std_logic;

  signal TX_WRITE_DATA             : std_logic_vector(15 downto 0);

  signal TX_READ_DATA              : std_logic_vector(15 downto 0);

  signal TX_WRITE_ADDRESS          : integer range 0 to 1513;

  signal TX_WRITE_ADDRESS_DEL      : integer range 0 to 1513;

  signal TX_READ_ADDRESS           : integer range 0 to 1513;

  signal TX_CRC                    : std_logic_vector(31 downto 0);

  signal TX_IN_COUNT               : integer range 0 to 1513;

  signal TX_OUT_COUNT              : integer range 0 to 1513;

  signal TX_PACKET_LENGTH          : std_logic_vector(15 downto 0);

  signal GO, GO_DEL, GO_SYNC       : std_logic;

  signal DONE, DONE_DEL, DONE_SYNC : std_logic;

  signal S_TX_ACK                  : std_logic;

  --RX signals

  signal RX_WRITE_ADDRESS          : unsigned(ADDRESS_BITS - 1 downto 0);

  signal RX_READ_ADDRESS           : unsigned(ADDRESS_BITS - 1 downto 0);

  signal RX_START_ADDRESS          : unsigned(ADDRESS_BITS - 1 downto 0);

  signal RX_PACKET_LENGTH          : unsigned(ADDRESS_BITS - 1 downto 0);

  signal RX_START_ADDRESS_BUFFER   : ADDRESS_ARRAY;

  signal RX_PACKET_LENGTH_BUFFER   : ADDRESS_ARRAY;

  signal RX_WRITE_BUFFER           : integer range 0 to 31;

  signal RX_READ_BUFFER            : integer range 0 to 31;

  signal RX_BUFFER_BUSY            : std_logic_vector(31 downto 0);

  signal RX_BUFFER_BUSY_DEL        : std_logic_vector(31 downto 0);

  signal RX_BUFFER_BUSY_SYNC       : std_logic_vector(31 downto 0);

  signal RX_START_ADDRESS_SYNC     : unsigned(ADDRESS_BITS - 1 downto 0);

  signal RX_PACKET_LENGTH_SYNC     : unsigned(ADDRESS_BITS - 1 downto 0);

  signal RX_END_ADDRESS            : unsigned(ADDRESS_BITS - 1 downto 0);

  signal RX_WRITE_DATA             : std_logic_vector(15 downto 0);

  signal RX_WRITE_ENABLE           : std_logic;

  signal RX_ERROR                  : std_logic;

  signal RX_CRC                    : std_logic_vector(31 downto 0);

  signal RXD_D                     : std_logic_vector(7 downto 0);

  signal RXDV_D                    : std_logic;

  signal RXER_D                    : std_logic;

begin

  --This process is in the local clock domain. 

  --It gets data and puts it into a RAM.

  --Once a packets worth of data has been stored it is

  --sent to the packet sending state machine.

  TX_PACKET_FSM : process

  begin

    wait until rising_edge(CLK);

    TX_WRITE <= '0';

    case TX_PACKET_STATE is

      when GET_LENGTH =>

        S_TX_ACK <= '1';

        if S_TX_ACK = '1' and TX_STB = '1' then

          S_TX_ACK <= '0';

          TX_PACKET_LENGTH <= TX;

                TX_IN_COUNT <= 2;

          TX_PACKET_STATE <= GET_DATA;

        end if;

      when GET_DATA =>

        S_TX_ACK <= '1';

        if S_TX_ACK = '1' and TX_STB = '1' then

          TX_WRITE_DATA <= TX;

          TX_WRITE <= '1';

          if TX_IN_COUNT >= unsigned(TX_PACKET_LENGTH) then

            TX_PACKET_STATE <= SEND_PACKET;

            S_TX_ACK <= '0';

          else

            TX_WRITE_ADDRESS <= TX_WRITE_ADDRESS + 1;

            TX_IN_COUNT <= TX_IN_COUNT + 2;

          end if;

        end if;

      when SEND_PACKET =>

        GO <= '1';

        TX_WRITE_ADDRESS <= 0;

        if DONE_SYNC = '1' then

          GO <= '0';

          TX_PACKET_STATE <= WAIT_NOT_DONE;

        end if;

      when WAIT_NOT_DONE =>

        if DONE_SYNC = '0' then

          TX_PACKET_STATE <= GET_LENGTH;

        end if;

    end case;

    if RST = '1' then

      TX_PACKET_STATE <= GET_LENGTH;

      TX_WRITE_ADDRESS <= 0;

      S_TX_ACK <= '0';

      GO <= '0';

    end if;

  end process TX_PACKET_FSM;

  TX_ACK <= S_TX_ACK;

  --This process writes data into a dual port RAM

  WRITE_DUAL_PORT_MEMORY : process

  begin

    wait until rising_edge(CLK);

    TX_WRITE_ADDRESS_DEL <= TX_WRITE_ADDRESS;

    if TX_WRITE = '1' then

      TX_MEMORY(TX_WRITE_ADDRESS_DEL) := TX_WRITE_DATA;

    end if;

  end process;

  --This process read data from a dual port RAM

  READ_DUAL_PORT_MEMORY : process

  begin

    wait until rising_edge(CLK_125_MHZ);

    TX_READ_DATA <= TX_MEMORY(TX_READ_ADDRESS);

  end process;

  --This process synchronises ethernet signals

  --to the local clock domain

  LOCAL_TO_CLK_125 : process

  begin

    wait until rising_edge(CLK_125_MHZ);

    GO_DEL <= GO; GO_SYNC <= GO_DEL;

  end process;

  --This process synchronises local signals to the ethernet clock domain

  CLK_125_TO_LOCAL : process

  begin

    wait until rising_edge(CLK);

    DONE_DEL <= DONE; DONE_SYNC <= DONE_DEL;

  end process;

  --Transmit the stored packet via the phy.

  TX_PHY_FSM : process

  begin

    wait until rising_edge(CLK_125_MHZ);

    case TX_PHY_STATE is

      when WAIT_NEW_PACKET =>

        if GO_SYNC = '1' then

          TX_PHY_STATE <= PREAMBLE_0;

          TX_READ_ADDRESS <= 0;

          TX_OUT_COUNT <= to_integer(unsigned(TX_PACKET_LENGTH)-1);

        end if;

      when PREAMBLE_0 =>

        TXD <= X"55";

        TX_PHY_STATE <= PREAMBLE_1;

        TXEN <= '1';

      when PREAMBLE_1 =>

        TXD <= X"55";

        TX_PHY_STATE <= PREAMBLE_2;

      when PREAMBLE_2 =>

        TXD <= X"55";

        TX_PHY_STATE <= PREAMBLE_3;

      when PREAMBLE_3 =>

        TXD <= X"55";

        TX_PHY_STATE <= PREAMBLE_4;

      when PREAMBLE_4 =>

        TXD <= X"55";

        TX_PHY_STATE <= PREAMBLE_5;

      when PREAMBLE_5 =>

        TXD <= X"55";

        TX_PHY_STATE <= PREAMBLE_6;

      when PREAMBLE_6 =>

        TXD <= X"55";

        TX_PHY_STATE <= SFD;

      when SFD =>

        TXD <= X"D5";

        TX_PHY_STATE <= SEND_DATA_HI;

        TX_CRC <= X"FFFFFFFF";

      when SEND_DATA_HI =>

        TX_CRC <= NEXTCRC32_D8(TX_READ_DATA(15 downto 8), TX_CRC);

        TXD <= TX_READ_DATA(15 downto 8);

        If TX_OUT_COUNT = 0 then

          TX_PHY_STATE <= SEND_CRC_3;

        else

                      TX_PHY_STATE <= SEND_DATA_LO;

          TX_READ_ADDRESS <= TX_READ_ADDRESS + 1;

          TX_OUT_COUNT <= TX_OUT_COUNT - 1;

        end if;

      when SEND_DATA_LO =>

        TX_CRC   <= NEXTCRC32_D8(TX_READ_DATA(7 downto 0), TX_CRC);

        TXD   <= TX_READ_DATA(7 downto 0);

        If TX_OUT_COUNT = 0 then

          TX_PHY_STATE <= SEND_CRC_3;

        else

          TX_PHY_STATE <= SEND_DATA_HI;

          TX_OUT_COUNT <= TX_OUT_COUNT - 1;

        end if;

      when SEND_CRC_3 =>

        TXD <= not REVERSED(TX_CRC(31 downto  24));

        TX_PHY_STATE <= SEND_CRC_2;

      when SEND_CRC_2 =>

        TXD <= not REVERSED(TX_CRC(23 downto  16));

        TX_PHY_STATE <= SEND_CRC_1;

      when SEND_CRC_1 =>

        TXD <= not REVERSED(TX_CRC(15 downto   8));

        TX_PHY_STATE <= SEND_CRC_0;

      when SEND_CRC_0 =>

        TXD <= not REVERSED(TX_CRC(7  downto   0));

        TX_PHY_STATE <= DONE_STATE;

      when DONE_STATE =>

        TXEN <= '0';

        DONE <= '1';

        if GO_SYNC = '0' then

          TX_PHY_STATE <= WAIT_NEW_PACKET;

          DONE <= '0';

        end if;

    end case;

    if RST = '1' then

      TXEN <= '0';

      TX_PHY_STATE <= WAIT_NEW_PACKET;

      DONE <= '0';

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

    end if;

  end process TX_PHY_FSM;

  TXER   <= '0';

  GTXCLK <= CLK_125_MHZ;

  --This process reads data out of the phy and puts it into a buffer.

  --There are many buffers on the RX side to cope with data arriving at

  --a high rate. If a very large packet is received, followed by many small

  --packets, a large number of packets need to be stored.

  RX_PHY_FSM : process

  begin

    wait until rising_edge(RXCLK);

    RX_WRITE_ENABLE <= '0';

    RXDV_D <= RXDV;

    RXER_D <= RXER;

    RXD_D <= RXD;

    case RX_PHY_STATE is

      when WAIT_START =>

        if RXDV_D = '1' and RXD_D = X"55" then

          RX_PHY_STATE <= PREAMBLE;

          RX_ERROR <= '0';

        end if;

      when PREAMBLE =>

        if RXD_D = X"d5" then

          RX_PHY_STATE <= DATA_HIGH;

          RX_START_ADDRESS <= RX_WRITE_ADDRESS;

          RX_PACKET_LENGTH <= to_unsigned(0, ADDRESS_BITS);

          RX_CRC <= X"ffffffff";

        elsif RXD_D /= X"55" or RXDV_D = '0' then

          RX_PHY_STATE <= WAIT_START;

        end if;

      when DATA_HIGH =>

        RX_WRITE_DATA(15 downto 8) <= RXD_D;

        if RXDV_D = '1' then

          RX_PACKET_LENGTH <= RX_PACKET_LENGTH + 1;

          RX_PHY_STATE <= DATA_LOW;

          RX_CRC <= nextCRC32_D8(RXD_D, RX_CRC);

        else

          RX_PHY_STATE <= END_OF_FRAME;

        end if;

      when DATA_LOW =>

        RX_WRITE_DATA(7 downto 0) <= RXD_D;

        RX_WRITE_ENABLE <= '1';

        if RXDV_D = '1' then

          RX_PACKET_LENGTH <= RX_PACKET_LENGTH + 1;

          RX_PHY_STATE <= DATA_HIGH;

          RX_CRC <= nextCRC32_D8(RXD_D, RX_CRC);

        else

          RX_PHY_STATE <= END_OF_FRAME;

        end if;

      when END_OF_FRAME =>

        if RX_ERROR = '1' then

          RX_PHY_STATE <= WAIT_START;

        elsif RX_PACKET_LENGTH < 64 then

          RX_PHY_STATE <= WAIT_START;

        elsif RX_PACKET_LENGTH > 1518 then

          RX_PHY_STATE <= WAIT_START;

        elsif RX_CRC /= X"C704dd7B" then

          RX_PHY_STATE <= WAIT_START;

        else

          RX_PHY_STATE <= NOTIFY_NEW_PACKET;

        end if;

      when NOTIFY_NEW_PACKET =>

        RX_PHY_STATE <= WAIT_START;

        RX_START_ADDRESS_BUFFER(RX_WRITE_BUFFER) <= RX_START_ADDRESS;

        RX_PACKET_LENGTH_BUFFER(RX_WRITE_BUFFER) <= RX_PACKET_LENGTH;

        if RX_WRITE_BUFFER = 31 then

          RX_WRITE_BUFFER <= 0;

        else

          RX_WRITE_BUFFER <= RX_WRITE_BUFFER + 1;

        end if;

    end case;

    if RXER_D = '1' then

      RX_ERROR <= '1';

    end if;

    if RST = '1' then

      RX_PHY_STATE <= WAIT_START;

    end if;

  end process RX_PHY_FSM;

  --generate a signal for each buffer to indicate that is is being used.

  GENERATE_BUFFER_BUSY : process

  begin

    wait until rising_edge(RXCLK);

    for I in 0 to 31 loop

      if I = RX_WRITE_BUFFER then

        RX_BUFFER_BUSY(I) <= '1';

      else

        RX_BUFFER_BUSY(I) <= '0';

      end if;

    end loop;

  end process GENERATE_BUFFER_BUSY;

  --This is the memory that implements the RX buffers

  WRITE_RX_MEMORY : process

  begin

    wait until rising_edge(RXCLK);

    if RX_WRITE_ENABLE = '1' then

      RX_MEMORY(to_integer(RX_WRITE_ADDRESS)) := RX_WRITE_DATA;

      RX_WRITE_ADDRESS <= RX_WRITE_ADDRESS + 1;

    end if;

    if RST = '1' then

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