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//-----------------------------------------------------------------------------

// Title      : 8-bit Client to Local-link Receiver FIFO

// Project    : Virtex-4 Embedded Tri-Mode Ethernet MAC Wrapper

// File       : rx_client_fifo_8.v

// Version    : 4.8

//-----------------------------------------------------------------------------

//

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//-----------------------------------------------------------------------------

// Description: This is the receiver side local link fifo for the design example

//              of the Virtex-4 Ethernet MAC Wrapper core.

//

//              The FIFO is created from 2 Block RAMs of size 2048

//              words of 8-bits per word, giving a total frame memory capacity

//              of 4096 bytes.

//

//              Frame data received from the MAC receiver is written into the

//              FIFO on the wr_clk.  An End Of Frame marker is written to the

//              BRAM parity bit on the last byte of data stored for a frame.

//              This acts as frame deliniation.

//

//              The rx_good_frame and rx_bad_frame signals are used to

//              qualify the frame.  A frame for which rx_bad_frame was

//              asserted will cause the FIFO write address pointer to be

//              reset to the base address of that frame.  In this way

//              the bad frame will be overwritten with the next received

//              frame and is therefore dropped from the FIFO.

//

//              Frames will also be dropped from the FIFO if an overflow occurs. 

//              If there is not enough memory capacity in the FIFO to store the 

//              whole of an incoming frame, the write address pointer will be

//              reset and the overflow signal asserted.

//

//              When there is at least one complete frame in the FIFO,

//              the 8 bit Local-link read interface will be enabled allowing

//              data to be read from the fifo.

//

//              The FIFO has been designed to operate with different clocks

//              on the write and read sides.  The read clock (locallink clock)

//              should always operate at an equal or faster frequency

//              than the write clock (client clock).

//

//              The FIFO is designed to work with a minimum frame length of 8 bytes.

//

//              The FIFO memory size can be increased by expanding the rd_addr

//              and wr_addr signal widths, to address further BRAMs.

//

//              Requirements :

//              * Minimum frame size of 8 bytes

//              * Spacing between good/bad frame flags is at least 64 clock cycles

//              * Wr clock is 125MHz downto 1.25MHz

//              * Rd clock is downto 20MHz

//

//-------------------------------------------------------------------------------

`timescale 1ps / 1ps

module rx_client_fifo_8

     (

        // Local-link Interface

        rd_clk,

        rd_sreset,

        rd_data_out,

        rd_sof_n,

        rd_eof_n,

        rd_src_rdy_n,

        rd_dst_rdy_n,

        rx_fifo_status,

        // Client Interface

        wr_sreset,

        wr_clk,

        wr_enable,

        rx_data,

        rx_data_valid,

        rx_good_frame,

        rx_bad_frame,

        overflow

        );

  //---------------------------------------------------------------------------

  // Define Interface Signals

  //--------------------------------------------------------------------------

  // Local-link Interface

  input        rd_clk;

  input        rd_sreset;

  output [7:0] rd_data_out;

  output       rd_sof_n;

  output       rd_eof_n;

  output       rd_src_rdy_n;

  input        rd_dst_rdy_n;

  output [3:0] rx_fifo_status;

  // Client Interface

  input        wr_sreset;

  input        wr_clk;

  input        wr_enable;

  input [7:0]  rx_data;

  input        rx_data_valid;

  input        rx_good_frame;

  input        rx_bad_frame;

  output       overflow;

  reg          rd_sof_n;

  wire         rd_eof_n;

  reg          rd_src_rdy_n;

  reg [7:0]    rd_data_out;

  //---------------------------------------------------------------------------

  // Define Internal Signals

  //---------------------------------------------------------------------------

  wire        GND;

  wire        VCC;

  wire [7:0]  GND_BUS;

  // Encode rd_state_machine states   

  parameter WAIT_s = 3'b000;      parameter QUEUE1_s = 3'b001;

  parameter QUEUE2_s = 3'b010;    parameter QUEUE3_s = 3'b011;

  parameter QUEUE_SOF_s = 3'b100; parameter SOF_s = 3'b101;

  parameter DATA_s = 3'b110;      parameter EOF_s = 3'b111;

  reg [2:0]   rd_state;

  reg [2:0]   rd_nxt_state;

  // Encode wr_state_machine states 

  parameter IDLE_s = 3'b000; parameter FRAME_s = 3'b001;

  parameter END_s= 3'b010;   parameter GF_s = 3'b011;

  parameter BF_s = 3'b100;   parameter OVFLOW_s = 3'b101;

  reg  [2:0]  wr_state;

  reg  [2:0]  wr_nxt_state;

  wire        wr_en;

  wire        wr_en_u;

  wire        wr_en_l;

  reg  [11:0] wr_addr;

  wire        wr_addr_inc;

  wire        wr_start_addr_load;

  wire        wr_addr_reload;

  reg  [11:0] wr_start_addr;

  reg  [7:0]  wr_data_bram;

  reg  [7:0]  wr_data_pipe[0:1];

  reg  [0:0]  wr_eof_bram;

  reg         wr_dv_pipe[0:1];

  reg         wr_gf_pipe[0:1];

  reg         wr_bf_pipe[0:1];

  reg         frame_in_fifo;

  reg  [11:0] rd_addr;

  wire        rd_addr_inc;

  wire        rd_addr_reload;

  wire [7:0]  rd_data_bram_u;

  wire [7:0]  rd_data_bram_l;

  reg  [7:0]  rd_data_pipe_u;

  reg  [7:0]  rd_data_pipe_l;

  reg  [7:0]  rd_data_pipe;

  wire [0:0]  rd_eof_bram_u;

  wire [0:0]  rd_eof_bram_l;

  reg         rd_en;

  reg         rd_bram_u;

  reg         rd_bram_u_reg;

  wire        rd_pull_frame;

  reg         rd_eof;

  reg         wr_store_frame_tog;

  reg         rd_store_frame_tog;

  reg         rd_store_frame_sync;

  reg         rd_store_frame_delay;

  reg         rd_store_frame;

  reg  [8:0]  rd_frames;

  reg         wr_fifo_full;

  reg  [11:0] rd_addr_gray;

  reg  [11:0] wr_rd_addr_gray_sync;

  reg  [11:0] wr_rd_addr_gray;

  wire [11:0] wr_rd_addr;

  reg  [11:0] wr_addr_diff;

  reg  [3:0]  wr_fifo_status;

  reg         rd_eof_n_int;

  reg  [1:0]  rd_valid_pipe;

  //---------------------------------------------------------------------------

  // Attributes for FIFO simulation and synthesis

  //---------------------------------------------------------------------------

  // ASYNC_REG attributes added to simulate actual behaviour under

  // asynchronous operating conditions.

  // synthesis attribute ASYNC_REG of rd_store_frame_tog is "TRUE";

  // synthesis attribute ASYNC_REG of wr_rd_addr_gray_sync is "TRUE";

  // WRITE_MODE attributes added to Block RAM to mitigate port contention

  // synthesis attribute WRITE_MODE_A of ramgen_u is "READ_FIRST";

  // synthesis attribute WRITE_MODE_B of ramgen_u is "READ_FIRST";

  // synthesis attribute WRITE_MODE_A of ramgen_l is "READ_FIRST";

  // synthesis attribute WRITE_MODE_B of ramgen_l is "READ_FIRST";

  //---------------------------------------------------------------------------

  // Functions for gray code conversion

  //---------------------------------------------------------------------------   

  function [11:0] bin_to_gray;

  input    [11:0] bin;

  integer         i;

  begin

     for (i=0;i<12;i=i+1)

        begin

          if (i == 11)

             bin_to_gray[i] = bin[i];

          else

             bin_to_gray[i] = bin[i+1] ^ bin[i];

        end

  end

  endfunction

  function [11:0] gray_to_bin;

  input   [11:0] gray;

  integer        i;

  begin

     for (i=11;i>=0;i=i-1)

        begin

          if (i == 11)

            gray_to_bin[i] = gray[i];

          else

            gray_to_bin[i] = gray_to_bin[i+1] ^ gray[i];

        end

  end

  endfunction // gray_to_bin

  //---------------------------------------------------------------------------

  // Begin FIFO architecture

  //---------------------------------------------------------------------------

  assign GND     = 1'b0;

  assign VCC     = 1'b1;

  assign GND_BUS = 8'b0;

  //---------------------------------------------------------------------------

  // Read State machines and control

  //---------------------------------------------------------------------------

  // local link state machine

  // states are WAIT, QUEUE1, QUEUE2, QUEUE3, SOF, DATA, EOF

  // clock state to next state

  always @(posedge rd_clk)

  begin

     if (rd_sreset == 1'b1)

        rd_state <= WAIT_s;

     else

        rd_state <= rd_nxt_state;

  end

  assign rd_eof_n = rd_eof_n_int;

  // decode next state, combinatorial

  always @(rd_state or frame_in_fifo or rd_eof or rd_dst_rdy_n or

           rd_eof_n_int or rd_valid_pipe)

  begin

     case (rd_state)

        WAIT_s : begin

           // wait till there is a full frame in the fifo

           // then start to load the pipeline

           if (frame_in_fifo == 1'b1 && rd_eof_n_int == 1'b1)

              rd_nxt_state <= QUEUE1_s;

           else

              rd_nxt_state <= WAIT_s;

           end

        QUEUE1_s : begin

           // load the output pipeline

           // this takes three clocks

           rd_nxt_state <= QUEUE2_s;

           end

        QUEUE2_s : begin

           rd_nxt_state <= QUEUE3_s;

           end

        QUEUE3_s : begin

           rd_nxt_state <= QUEUE_SOF_s;

           end

        QUEUE_SOF_s : begin

           // used mark sof at end of queue

              rd_nxt_state <= DATA_s;  // move straight to frame.

           end

        SOF_s : begin

           // used to mark sof when following straight from eof

           if (rd_dst_rdy_n == 1'b0)

              rd_nxt_state <= DATA_s;

           else

              rd_nxt_state <= SOF_s;

           end

        DATA_s : begin

           // When the eof marker is detected from the BRAM output

           // move to EOF state

           if (rd_dst_rdy_n == 1'b0 && rd_eof == 1'b1)

              rd_nxt_state <= EOF_s;

           else

              rd_nxt_state <= DATA_s;

           end

        EOF_s : begin

           // hold in this state until dst rdy is low

           // and eof bit is accepted on interface

           // If there is a frame in the fifo, then the next frame

           // will already be queued into the pipe line so move straight

           // to sof state.

           if (rd_dst_rdy_n == 1'b0)

              if (rd_valid_pipe[1] == 1'b1)

                 rd_nxt_state <= SOF_s;

              else

                 rd_nxt_state <= WAIT_s;

           else

              rd_nxt_state <= EOF_s;

           end

        default : begin

           rd_nxt_state <= WAIT_s;

           end

        endcase

  end

  // detect if frame in fifo was high 3 reads ago

  // this is used to ensure we only treat data in the pipeline as valid if

  // frame in fifo goes high at or before the eof of the current frame

  // It may be that there is valid data (i.e a partial packet has been written)

  // but until the end of that packet we do not know if it is a good packet

  always @(posedge rd_clk)

  begin

     if (rd_dst_rdy_n == 1'b0)

        rd_valid_pipe <= {rd_valid_pipe[0], frame_in_fifo};

  end

  // decode the output signals depending on current state.

  // decode sof signal.

  always @(posedge rd_clk)

  begin

     if (rd_sreset == 1'b1)

        rd_sof_n <= 1'b1;

     else

        case (rd_state)

           QUEUE_SOF_s :

              // no need to wait for dst rdy to be low, as there is valid data

              rd_sof_n <= 1'b0;

           SOF_s :

              // needed to wait till rd_dst_rdy is low to ensure eof signal has

              // been accepted onto the interface before asserting sof.

              if (rd_dst_rdy_n == 1'b0)

                 rd_sof_n <= 1'b0;

           default :

              // needed to wait till rd_dst_rdy is low to ensure sof signal has

              // been accepted onto the interface.

              if (rd_dst_rdy_n == 1'b0)

                 rd_sof_n <= 1'b1;

        endcase

  end

  // decode eof signal

  // check init value of this reg is 1.

  always @(posedge rd_clk)

  begin

     if (rd_sreset == 1'b1)

        rd_eof_n_int <= 1'b1;

     else if (rd_dst_rdy_n == 1'b0)

        // needed to wait till rd_dst_rdy is low to ensure penultimate byte of frame has

        // been accepted onto the interface before asserting eof and that

        // eof is accepted before moving on

        case (rd_state)

           EOF_s :

              rd_eof_n_int <= 1'b0;

           default :

              rd_eof_n_int <= 1'b1;

        endcase

           // queue sof is not needed if init value is 1

  end

  // decode data output

  always @(posedge rd_clk)

  begin

     if (rd_en == 1'b1)

        rd_data_out <= rd_data_pipe;

  end

  // decode the output scr_rdy signal

  // want to remove the dependancy of src_rdy from dst rdy

  // check init value of this reg is 1'b1

  always @(posedge rd_clk)

  begin

     if (rd_sreset == 1'b1)

        rd_src_rdy_n <= 1'b1;

     else

        case (rd_state)

           QUEUE_SOF_s :

              rd_src_rdy_n <= 1'b0;

           SOF_s :

              rd_src_rdy_n <= 1'b0;

           DATA_s :

              rd_src_rdy_n <= 1'b0;

           EOF_s :

              rd_src_rdy_n <= 1'b0;

           default :

              if (rd_dst_rdy_n == 1'b0)

                 rd_src_rdy_n <= 1'b1;

         endcase

  end

  // decode internal control signals

  // rd_en is used to enable the BRAM read and load the output pipe

  always @(rd_state or rd_dst_rdy_n)

  begin

     case (rd_state)

         WAIT_s :

              rd_en <= 1'b0;

         QUEUE1_s :

              rd_en <= 1'b1;

         QUEUE2_s :

              rd_en <= 1'b1;

         QUEUE3_s :

              rd_en <= 1'b1;

         QUEUE_SOF_s :

              rd_en <= 1'b1;

         default :

              rd_en <= !rd_dst_rdy_n;

         endcase

  end

  // rd_addr_inc is used to enable the BRAM read address to increment

  assign rd_addr_inc = rd_en;

  // When the current frame is output, if there is no frame in the fifo, then

  // the fifo must wait until a new frame is written in.  This requires the read

  // address to be moved back to where the new frame will be written.  The pipe

  // is then reloaded using the QUEUE states

  assign rd_addr_reload = (rd_state == EOF_s && rd_nxt_state == WAIT_s) ? 1'b1 : 1'b0;

  // Data is available if there is at leat one frame stored in the FIFO.

  always @(posedge rd_clk)

  begin

     if (rd_sreset == 1'b1)

        frame_in_fifo <= 1'b0;

     else

        if (rd_frames != 9'b0)

           frame_in_fifo <= 1'b1;

        else

           frame_in_fifo <= 1'b0;

  end

  // when a frame has been stored need to convert to rd clock domain for frame

  // count store.

  always @(posedge rd_clk)

  begin

     if (rd_sreset == 1'b1)

        begin

           rd_store_frame_tog  <= 1'b0;

           rd_store_frame_sync <= 1'b0;

           rd_store_frame_delay <= 1'b0;

           rd_store_frame      <= 1'b0;

        end

     else

        begin

           rd_store_frame_tog  <= wr_store_frame_tog;

           rd_store_frame_sync <= rd_store_frame_tog;

           rd_store_frame_delay <= rd_store_frame_sync;

           // edge detector

           if ((rd_store_frame_delay ^ rd_store_frame_sync) == 1'b1)

              rd_store_frame    <= 1'b1;

           else

              rd_store_frame    <= 1'b0;

        end

  end

  assign rd_pull_frame = (rd_state == SOF_s && rd_nxt_state != SOF_s) ? 1'b1 :

                         (rd_state == QUEUE_SOF_s && rd_nxt_state != QUEUE_SOF_s) ? 1'b1 : 1'b0;

  // Up/Down counter to monitor the number of frames stored within the

  // the FIFO. Note:  

  //    * decrements at the beginning of a frame read cycle

  //    * increments at the end of a frame write cycle

  always @(posedge rd_clk)

  begin

     if (rd_sreset == 1'b1)

        rd_frames <= 9'b0;

     else

        // A frame is written to the fifo in this cycle, and no frame is being

        // read out on the same cycle

        if (rd_store_frame == 1'b1 && rd_pull_frame == 1'b0)

           rd_frames <= rd_frames + 1;

        // A frame is being read out on this cycle and no frame is being

        // written on the same cycle

        else if (rd_store_frame == 1'b0 && rd_pull_frame == 1'b1)

           rd_frames <= rd_frames - 1;

  end

  //---------------------------------------------------------------------------

  // Write State machines and control

  //---------------------------------------------------------------------------

  // write state machine

  // states are IDLE, FRAME, EOF, GF, BF, OVFLOW

  // clock state to next state

  always @(posedge wr_clk)

  begin

     if (wr_sreset == 1'b1)

        wr_state <= IDLE_s;

     else if (wr_enable == 1'b1)

        wr_state <= wr_nxt_state;

  end

  // decode next state, combinatorial

  always @(wr_state or wr_dv_pipe[1] or wr_gf_pipe[1] or wr_bf_pipe[1] or wr_eof_bram[0] or wr_fifo_full)

  begin

     case (wr_state)

        IDLE_s : begin

           // there is data in the incoming pipeline when dv_pipe(1) goes high

           if (wr_dv_pipe[1] == 1'b1)

              wr_nxt_state <= FRAME_s;

           else

              wr_nxt_state <= IDLE_s;

           end

        FRAME_s : begin

              // if fifo is full then go to overflow state.

              // if the good or bad flag is detected the end

              // of the frame has been reached!

              // this transistion occurs when the gb flag

              // is on the clock edge immediately following

              // the end of the frame.

              // if the eof_bram signal is detected then data valid has

              // fallen low and the end of frame has been detected.

              if (wr_fifo_full == 1'b1)

                 wr_nxt_state <= OVFLOW_s;

              else if (wr_gf_pipe[1] == 1'b1)

                 wr_nxt_state <= GF_s;

              else if (wr_bf_pipe[1] == 1'b1)

                 wr_nxt_state <= BF_s;

              else if (wr_eof_bram[0] == 1'b1)

                 wr_nxt_state <= END_s;

              else

                 wr_nxt_state <= FRAME_s;

              end

           END_s : begin

              // if frame is full then go to overflow state

              // else wait until the good or bad flag has been received.

              if (wr_gf_pipe[1] == 1'b1)

                 wr_nxt_state <= GF_s;

              else if (wr_bf_pipe[1] == 1'b1)

                 wr_nxt_state <= BF_s;

              else

                 wr_nxt_state <= END_s;

              end

           GF_s : begin

              // wait for next frame

              wr_nxt_state <= IDLE_s;

              end

           BF_s : begin

              // wait for next frame

              wr_nxt_state <= IDLE_s;

              end

           OVFLOW_s : begin

              // wait until the good or bad flag received.

              if (wr_gf_pipe[1] == 1'b1 || wr_bf_pipe[1] == 1'b1)

                 wr_nxt_state <= IDLE_s;

              else

                 wr_nxt_state <= OVFLOW_s;

              end

           default : begin

              wr_nxt_state <= IDLE_s;

              end

        endcase

  end

  // decode control signals

  // wr_en is used to enable the BRAM write and loading of the input pipeline

  assign wr_en = (wr_state == FRAME_s) ? 1'b1 : 1'b0;

  // the upper and lower signals are used to distinguish between the upper and

  // lower BRAM

  assign wr_en_l = wr_en & !wr_addr[11];

  assign wr_en_u = wr_en & wr_addr[11];

  // increment the write address when we are receiving a frame

  assign wr_addr_inc = (wr_state == FRAME_s) ? 1'b1 : 1'b0;

  // if the fifo overflows or a frame is to be dropped, we need to move the

  // write address back to the start of the frame.  This allows the data to be

  // overwritten.

  assign wr_addr_reload = (wr_state == BF_s || wr_state == OVFLOW_s) ? 1'b1 : 1'b0;

  // the start address is saved when in the WAIT state

  assign wr_start_addr_load = (wr_state == IDLE_s) ? 1'b1 : 1'b0;

  // we need to know when a frame is stored, in order to increment the count of

  // frames stored in the fifo.

  always @(posedge wr_clk)

  begin  // process

     if (wr_sreset == 1'b1)

        wr_store_frame_tog <= 1'b0;

     else if (wr_enable == 1'b1)

        if (wr_state == GF_s)

           wr_store_frame_tog <= ! wr_store_frame_tog;

  end

  //---------------------------------------------------------------------------

  // Address counters

  //---------------------------------------------------------------------------

  // write address is incremented when write enable signal has been asserted

  always @(posedge wr_clk)

  begin

     if (wr_sreset == 1'b1)

        wr_addr <= 12'b0;

     else if (wr_enable == 1'b1)

        if (wr_addr_reload == 1'b1)

           wr_addr <= wr_start_addr;

        else if (wr_addr_inc == 1'b1)

           wr_addr <= wr_addr + 1;

  end

  // store the start address

  always @(posedge wr_clk)

  begin

     if (wr_sreset == 1'b1)

        wr_start_addr <= 12'b0;

     else if (wr_enable == 1'b1)

        if (wr_start_addr_load == 1'b1)

           wr_start_addr <= wr_addr;

  end

  // read address is incremented when read enable signal has been asserted

  always @(posedge rd_clk)

  begin

     if (rd_sreset == 1'b1)

        rd_addr <= 12'b0;

     else

        if (rd_addr_reload == 1'b1)

           rd_addr <= rd_addr - 2;

        else if (rd_addr_inc == 1'b1)

           rd_addr <= rd_addr + 1;

  end

  // which BRAM is read from is dependant on the upper bit of the address

  // space.  this needs to be registered to give the correct timing.

  always @(posedge rd_clk)

  begin

     if (rd_sreset == 1'b1)

        begin