Subversion Repositories srdydrdy_lib

// Send an ethernet packet over GMII

module gmii_driver

  (output reg [7:0] rxd,

   output reg       rx_dv,

   output reg       rx_clk);

  integer           startup_skew;

  reg [7:0]          rxbuf [0:2048];

  reg [31:0]         crc32_result;

  // begin start clock with random skew amount

  initial

    begin

      startup_skew = {$random} % 200;

      rx_clk = 0;

      rx_dv = 0;

      rxd   = 0;

      repeat (startup_skew) #0.1;

      forever rx_clk = #4 ~rx_clk;

    end

  // Copied from: http://www.mindspring.com/~tcoonan/gencrc.v

  // 

  // Generate a (DOCSIS) CRC32.

  //

  // Uses the GLOBAL variables:

  //

  //    Globals referenced:

  //       parameter    CRC32_POLY = 32'h04C11DB7;

  //       reg [ 7:0]   crc32_packet[0:255];

  //       integer      crc32_length;

  //

  //    Globals modified:

  //       reg [31:0]   crc32_result;

  //

  localparam    CRC32_POLY = 32'h04C11DB7;

  task gencrc32;

    input [31:09] crc32_length;

    integer     cbyte, cbit;

    reg         msb;

    reg [7:0]    current_cbyte;

    reg [31:0]   temp;

    begin

      crc32_result = 32'hffffffff;

      for (cbyte = 0; cbyte < crc32_length; cbyte = cbyte + 1) begin

        current_cbyte = rxbuf[cbyte];

         for (cbit = 0; cbit < 8; cbit = cbit + 1) begin

            msb = crc32_result[31];

            crc32_result = crc32_result << 1;

            if (msb != current_cbyte[cbit]) begin

               crc32_result = crc32_result ^ CRC32_POLY;

               crc32_result[0] = 1;

            end

         end

      end

      // Last step is to "mirror" every bit, swap the 4 bytes, and then complement each bit.

      //

      // Mirror:

      for (cbit = 0; cbit < 32; cbit = cbit + 1)

         temp[31-cbit] = crc32_result[cbit];

      // Swap and Complement:

      crc32_result = ~{temp[7:0], temp[15:8], temp[23:16], temp[31:24]};

   end

endtask

  task send_packet;

    input [47:0] da, sa;

    input [15:0] length;

    integer      p;

    begin

      { rxbuf[0],rxbuf[1],rxbuf[2],rxbuf[3],rxbuf[4],rxbuf[5] } = da;

      { rxbuf[6],rxbuf[7],rxbuf[8],rxbuf[9],rxbuf[10],rxbuf[11] } = sa;

      for (p=12; p<length; p=p+1)

        rxbuf[p] = $random;

      gencrc32 (length);

      { rxbuf[length-4], rxbuf[length-3],

        rxbuf[length-2], rxbuf[length-1] } = crc32_result;

      $display ("%m : Sending packet DA=%x SA=%x of length %0d", da, sa, length);

      repeat (7)

        begin

          @(posedge rx_clk);

          rx_dv <= #1 1;

          rxd   <= #1 `GMII_PRE;

        end

      @(posedge rx_clk);

      rxd <= #1 `GMII_SFD;

      p = 0;

      while (p < length)

        begin

          @(posedge rx_clk);

          rxd <= #1 rxbuf[p];

          p = p + 1;

        end

      // complete 12B inter frame gap

      repeat (12)

        begin

          @(posedge rx_clk);

          rx_dv <= #1 0;

          rxd   <= #1 0;

        end

    end

  endtask // send_packet

endmodule // gmii_driver