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//////////////////////////////////////////////////////////////////////

////                                                              ////

////  SMII Receiver/Decoder (usually at PHY end)                  ////

////                                                              ////

////  Description                                                 ////

////  Low pin count serial MII ethernet interface                 ////

////                                                              ////

////  To Do:                                                      ////

////   -                                                          ////

////                                                              ////

////  Author(s):                                                  ////

////      - Michael Unneback, unneback@opencores.org              ////

////        ORSoC AB          michael.unneback@orsoc.se           ////

////      - Julius Baxter, jb@orsoc.se                            ////

////                                                              ////

//////////////////////////////////////////////////////////////////////

////                                                              ////

//// Copyright (C) 2009 Authors and OPENCORES.ORG                 ////

////                                                              ////

//// This source file may be used and distributed without         ////

//// restriction provided that this copyright statement is not    ////

//// removed from the file and that any derivative work contains  ////

//// the original copyright notice and the associated disclaimer. ////

////                                                              ////

//// This source file is free software; you can redistribute it   ////

//// and/or modify it under the terms of the GNU Lesser General   ////

//// Public License as published by the Free Software Foundation; ////

//// either version 2.1 of the License, or (at your option) any   ////

//// later version.                                               ////

////                                                              ////

//// This source is distributed in the hope that it will be       ////

//// useful, but WITHOUT ANY WARRANTY; without even the implied   ////

//// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR      ////

//// PURPOSE.  See the GNU Lesser General Public License for more ////

//// details.                                                     ////

////                                                              ////

//// You should have received a copy of the GNU Lesser General    ////

//// Public License along with this source; if not, download it   ////

//// from http://www.opencores.org/lgpl.shtml                     ////

////                                                              ////

//////////////////////////////////////////////////////////////////////

module smii_phy

  (

   // SMII

    input     smii_tx,

    input     smii_sync,

    output reg    smii_rx,

   // MII

   // TX

   /* ALL I/Os swapped compared to SMII on MAC end MAC - jb */

    output reg [3:0] ethphy_mii_tx_d,

    output reg       ethphy_mii_tx_en,

    output reg       ethphy_mii_tx_err,

    input            ethphy_mii_tx_clk,

   // RX

    input [3:0]      ethphy_mii_rx_d,

    input            ethphy_mii_rx_dv,

    input            ethphy_mii_rx_err,

    input            ethphy_mii_rx_clk,

    input            ethphy_mii_mcoll,

    input            ethphy_mii_crs,

    input            fast_ethernet,

    input            duplex,

    input            link,

   // internal

    //input [10:1] state,

   // clock and reset

    input        clk, /* Global reference clock for both SMII modules */

    input        rst_n

   );

   reg [3:0]      rx_tmp;

   reg           jabber = 0;

   reg           mtx_clk_tmp, mrx_clk_tmp;

   reg [3:0]      tx_cnt;

   reg [3:0]      rx_cnt;

/**************************************************************************/

/* Counters */

/**************************************************************************/

   /* Generate the state counter, based on incoming sync signal */

   /* 10-bit shift register, indicating where we are */

   reg [10:1]    state_shiftreg;

   /* A wire hooked up from bit 0 with the last byte of the state counter/shiftreg */

   wire [7:0] state_shiftreg_top_byte;

   assign state_shiftreg_top_byte[7:0] = state_shiftreg[10:3];

   always @(posedge clk)

     begin

        if (!rst_n)

          begin

             state_shiftreg <= 10'b0000000001;

          end

        else

          begin

             if (smii_sync) /* sync signal from MAC */

               state_shiftreg <= 10'b0000000010;

             else if (state_shiftreg[10])

               state_shiftreg <= 10'b0000000001;

             else

               state_shiftreg[10:2] <= state_shiftreg[9:1];

          end // else: !if(!rst_n)      

     end // always @ (posedge clk)

   /* counter from 0 to 9, counting the 10-bit segments we'll transmit

    via SMII*/

   reg [3:0] segment_ctr;

   always @(posedge clk)

     begin

        if(!rst_n)

          segment_ctr <= 4'h0;

        else

          begin

             if(fast_ethernet) /* If using 100Mbs, then each segment is

                            different, we don't count the repeats */

               segment_ctr <= 4'h0;

             else if (state_shiftreg[10])

               if (segment_ctr == 4'h9) /* Wrap */

                 segment_ctr <= 4'h0;

               else /* Increment */

                 segment_ctr <= segment_ctr + 1'b1;

          end

     end // always @ (posedge clk)

/**************************************************************************/

/* RX path logic PHY->(MII->SMII)->MAC */

/**************************************************************************/

   reg rx_nibble_sel, rx_byte_valid;

   reg [7:0] rx_data_byte_rx_clk;

   reg [4:0] rx_dv_nib_0;

   reg       rx_nib_first,rx_nib_first_r;  // if high, nib_0 contains the "first" of the pair of nibs

   reg [3:0] rx_segment_begin_num;

   // Allow us to check if RX DV has been low for a while

   reg [3:0] rx_dv_long_low_sr;

   wire      dv_long_low;

   always @(posedge ethphy_mii_rx_clk)

     rx_dv_long_low_sr[3:0] <= {rx_dv_long_low_sr[2:0], ethphy_mii_rx_dv};

   assign rx_dv_long_low = ~(|rx_dv_long_low_sr);

   reg      rx_dv;

   wire [8:0] rx_fifo_out;

   wire       rx_fifo_empty,rx_fifo_almost_empty;

   reg        rx_fifo_pop;

   always @(posedge ethphy_mii_rx_clk or negedge rst_n)

     begin

        if(!rst_n)

          begin

             rx_dv_nib_0 <= 0;

             rx_nib_first <= 0;

             rx_nib_first_r <= 0;

          end

        else

          begin

             if (!rx_nib_first)

               rx_dv_nib_0 <= {ethphy_mii_rx_dv,ethphy_mii_rx_d};

             if(ethphy_mii_rx_dv)

               rx_nib_first <= ~rx_nib_first;

             rx_nib_first_r <= rx_nib_first;

          end

     end // always @ (posedge ethphy_mii_rx_clk or negedge rst_n)

     always @(posedge clk or negedge rst_n)

       begin

          if (!rst_n) rx_fifo_pop <= 0;

          else rx_fifo_pop <= (rx_fifo_almost_empty) ? (rx_fifo_pop ? ~rx_fifo_empty : rx_fifo_pop) : 1;

          rx_dv <= (state_shiftreg[10] & (((rx_segment_begin_num == (segment_ctr-1)) && !fast_ethernet)| fast_ethernet)) ? (rx_fifo_pop) : rx_dv;

       end

   always @(posedge clk)

     begin

        /* remember which counter value we were at when rx enable/valid

         went high.

         This is only useful when not doing fast ethernet*/

        /* rx en has gone high - remember the sequence number we're in */

        if ((rx_segment_begin_num == 4'hf) & (~rx_dv_long_low))

          rx_segment_begin_num <= segment_ctr;

        /* If rx enable goes low again, reset the segment number */

        if (rx_dv_long_low)

             /* reset to 0xf */

             rx_segment_begin_num <= 4'hf;

     end

     /* A fifo, storing RX bytes coming from the PHY interface */

   generic_fifo #(9, 64) rx_fifo

     (

      // Outputs

      .psh_full                         (),

      .pop_q                            (rx_fifo_out),

      .pop_empty                        (rx_fifo_empty),

      .almost_empty                     (rx_fifo_almost_empty),

      // Inputs

      .async_rst_n                      (rst_n),

      .psh_clk                          (ethphy_mii_rx_clk),

      .psh_we                           (rx_nib_first_r),

      .psh_d                            ({ethphy_mii_rx_err,ethphy_mii_rx_d,rx_dv_nib_0[3:0]}),

      .pop_clk                          (clk),

      .pop_re                           ((state_shiftreg[1] & rx_fifo_pop)&(((rx_segment_begin_num == segment_ctr) && !fast_ethernet)| fast_ethernet)));

  `ifdef RX_SYNC_1

    /* Assign the rx line out */

   always @(posedge clk)

    smii_rx <= state_shiftreg[1] ? ethphy_mii_crs : /* 1st bit is MII CRS */

                    state_shiftreg[2] ? ((rx_dv & (segment_ctr==4'h0) & !fast_ethernet) |

                                         rx_dv) :

               // inter-frame status byte or data byte

               state_shiftreg[3] ? (rx_dv ?  (rx_fifo_out[0]) : ethphy_mii_rx_err) :

               state_shiftreg[4] ? (rx_dv ?  (rx_fifo_out[1]) : fast_ethernet) :

               state_shiftreg[5] ? (rx_dv ?  (rx_fifo_out[2]) : duplex) :

               state_shiftreg[6] ? (rx_dv ?  (rx_fifo_out[3]) : link) :

               state_shiftreg[7] ? (rx_dv ?  (rx_fifo_out[4]) : jabber) :

               state_shiftreg[8] ? (rx_dv ?  (rx_fifo_out[5]) : 1) :

               state_shiftreg[9] ? (rx_dv ?  (rx_fifo_out[6]) : 0) :

               state_shiftreg[10] ? (rx_dv ?  (rx_fifo_out[7]) : 1) : 0;

  `else // !`ifdef RX_SYNC_1

       /* Assign the rx line out */

   always @(posedge clk)

    smii_rx <= state_shiftreg[10] ? ethphy_mii_crs : /* 1st bit is MII CRS */

                    state_shiftreg[1] ? ((rx_dv & (segment_ctr==4'h0) & !fast_ethernet) |

                                         rx_dv) :

               // inter-frame status byte or data byte

               state_shiftreg[2] ? (rx_dv ?  (rx_fifo_out[0]) : ethphy_mii_rx_err) :

               state_shiftreg[3] ? (rx_dv ?  (rx_fifo_out[1]) : fast_ethernet) :

               state_shiftreg[4] ? (rx_dv ?  (rx_fifo_out[2]) : duplex) :

               state_shiftreg[5] ? (rx_dv ?  (rx_fifo_out[3]) : link) :

               state_shiftreg[6] ? (rx_dv ?  (rx_fifo_out[4]) : jabber) :

               state_shiftreg[7] ? (rx_dv ?  (rx_fifo_out[5]) : 1) :

               state_shiftreg[8] ? (rx_dv ?  (rx_fifo_out[6]) : 0) :

               state_shiftreg[9] ? (rx_dv ?  (rx_fifo_out[7]) : 1) : 0;

  `endif // !`ifdef RX_SYNC_1

   /* Status seq.: CRS, DV, ER, Speed, Duplex, Link, Jabber, UPV, FCD, 1 */

   //    {1'b1,1'b0,1'b1,jabber,link,duplex,,ethphy_mii_rx_err});

/**************************************************************************/

/* TX path logic MAC->(SMII->MII)->PHY */

/**************************************************************************/

   /* We ignore the data when TX_EN bit is not high -

    it's only used in MAC to MAC comms*/

   /* Register the sequence appropriately as it comes in */

   reg tx_er_seqbit_scratch;

   reg tx_en_seqbit_scratch;

   reg [7:0] tx_data_byte_scratch;

   reg [2:0] tx_byte_to_phy; /* PHY sourced TX_CLK domain */

   wire      tx_fifo_empty, tx_fifo_almost_empty;

   wire      tx_fifo_full;

   wire [7:0] tx_fifo_q_dat;

   wire       tx_fifo_q_err;

   reg        tx_fifo_pop;

   reg [3:0]  tx_segment_begin_num;

   wire [3:0] tx_segment_load_num;

   assign tx_segment_load_num = (tx_segment_begin_num == 0) ? 4'h9 : tx_segment_begin_num - 1;

   /* Signal to tell us an appropriate time to copy the values out of the

    temp regs we put the incoming TX line into when we've received a

    sequence off the SMII TX line that has TX_EN high */

   wire      tx_seqbits_copy;

   assign tx_seqbits_copy = (

                             (

                              ((!fast_ethernet) & (segment_ctr == tx_segment_load_num)) |

                              fast_ethernet

                             )

                             & tx_en_seqbit_scratch & state_shiftreg[1]

                            );

   always @(posedge clk)

     begin

        /* remember which counter value we were at when tx enable/valid

         went high.

         This is only useful when not doing fast ethernet*/

        /* tx en has gone high - remember the sequence number we're in */

        if ((tx_segment_begin_num == 4'hf) & (tx_en_seqbit_scratch))

          tx_segment_begin_num <= segment_ctr;

        /* If tx enable goes low again, reset the segment number */

        if (!tx_en_seqbit_scratch)

             /* reset to 0xf */

             tx_segment_begin_num <= 4'hf;

     end

   always @(posedge clk)

     begin

        if (!rst_n)

          begin

             tx_er_seqbit_scratch <= 0;

             tx_en_seqbit_scratch <= 0;

             tx_data_byte_scratch <= 0;

          end

        else

          begin

             if(state_shiftreg[1])

               tx_er_seqbit_scratch <= smii_tx;

             if(state_shiftreg[2])

               tx_en_seqbit_scratch <= smii_tx;

             /* Preserve all but current bit of interest, as indicated

              by state vector bit (reversed, becuase we get MSbit

              first) and OR in the current smii_tx line value at this

              position*/

             if((|state_shiftreg[10:3]) & tx_en_seqbit_scratch)

               tx_data_byte_scratch <= (tx_data_byte_scratch & ~state_shiftreg_top_byte) |

                                       ({8{smii_tx}} & state_shiftreg_top_byte);

          end

     end // always @ (posedge clk)

   reg [3:0] nib;

   /* In the event we have a valid byte frame then get it to the

    PHY as quickly as possible - this is TX_CLK domain */

   always @(posedge ethphy_mii_tx_clk or negedge rst_n)

     begin

        if(!rst_n)

          begin

             tx_byte_to_phy <= 0;

             tx_fifo_pop <= 1'b0;

             /* Output MII registers to the PHY */

             ethphy_mii_tx_d <= 0;

             ethphy_mii_tx_en <= 0;

             ethphy_mii_tx_err <= 0;

          end

        else

          begin

             /* If fast_ethernet/100mbs we wait until the FIFO is full

              otherwise, we push out the byte each time we get one */

             //if((!tx_fifo_empty && !fast_ethernet) ||

             //(tx_fifo_full && fast_ethernet))

             if (!tx_fifo_almost_empty)

               begin

                  if(tx_byte_to_phy == 0)

                    begin

                       tx_byte_to_phy <= 1;

                       tx_fifo_pop <= 1;

                    end

               end

             /* FIFO control loop */

             if (tx_byte_to_phy == 1)/* Output bits 3-0 (bottom nibble ) */

               begin

                  ethphy_mii_tx_en <= 1;

                  tx_fifo_pop <= 0;

                  tx_byte_to_phy <= 2;

                  ethphy_mii_tx_d <= tx_fifo_q_dat[3:0];

                  nib <= tx_fifo_q_dat[7:4];

                  ethphy_mii_tx_err <= tx_fifo_q_err;

               end

             else if (tx_byte_to_phy == 2) /* Output bits 7-4 (top nibble) */

               begin

                  //ethphy_mii_tx_d <= tx_fifo_q_dat[7:4];

                  ethphy_mii_tx_d <= nib;

                  if(!tx_fifo_empty) /* Check if more in FIFO */

                    begin

                       tx_fifo_pop <= 1;

                       tx_byte_to_phy <= 1;

                    end

                  else /* Finish up */

                    begin

                       tx_byte_to_phy <= 3;

                       ethphy_mii_tx_en <= 0;

                    end

               end

             else if (tx_byte_to_phy == 3) /* De-assert TX_EN */

               begin

                  tx_byte_to_phy <= 2'b00;

               end

          end // else: !if(!rst_n)

     end // always @ (posedge ethphy_mii_tx_clk or negedge rst_n)

   /* A fifo, storing TX bytes coming from the SMII interface */

   generic_fifo #(9, 64) tx_fifo

     (

      // Outputs

      .psh_full                         (tx_fifo_full),

      .pop_q                            ({tx_fifo_q_err,tx_fifo_q_dat}),

      .pop_empty                        (tx_fifo_empty),

      .almost_empty                     (tx_fifo_almost_empty),

      // Inputs

      .async_rst_n                      (rst_n),

      .psh_clk                          (clk),

      .psh_we                           (tx_seqbits_copy),

      .psh_d                            ({tx_er_seqbit_scratch,tx_data_byte_scratch}),

      .pop_clk                          (ethphy_mii_tx_clk),

      .pop_re                           (tx_fifo_pop));

   //assign mcoll = mcrs & mtxen;

endmodule // smii_top

/* Generic fifo - this is bad, should probably be done some other way */

module generic_fifo (async_rst_n, psh_clk, psh_we, psh_d, psh_full, pop_clk, pop_re, pop_q, pop_empty, almost_empty);

   parameter dw = 8;

   parameter size = 16;

   parameter size_log_2 = 4;

   /* Asynch. reset, active low */

   input async_rst_n;

   /* Push side signals */

   input psh_clk;

   input psh_we;

   input [dw-1:0] psh_d;

   output         psh_full;

   /* Pop side signals */

   input          pop_clk;

   input          pop_re;

   //output reg [dw-1:0] pop_q;

   output reg [dw-1:0] pop_q;

   output              pop_empty;

   output wire         almost_empty;

   /* Actual FIFO memory */

   reg [dw-1:0]   fifo_mem [0:size-1];

   /* FIFO position ptr regs */

   reg [size_log_2 - 1 : 0 ]   wr_ptr, rd_ptr, ctr;

   integer     i;

   /* FIFO full signal for push side */

   //assign psh_full = (ptr == size-1) ? 1 : 0;

   /* This full logic means we all but one slot in the FIFO */

   assign psh_full = ctr == size;

   /* FIFO empty signal for pop side */

   //assign pop_empty = (ptr == 0) ? 1 : 0;

   //assign pop_empty = ctr==0;

   assign pop_empty = rd_ptr == wr_ptr;

   assign almost_empty = ctr < 2;

   always @(posedge pop_re or negedge async_rst_n)

     begin

        if (!async_rst_n)

          rd_ptr <= 0;

        else

          begin

             pop_q = fifo_mem[rd_ptr];

             rd_ptr <= rd_ptr + 1;

             ctr <= ctr - 1;

          end

     end

   always @(posedge psh_we or negedge async_rst_n)

     begin

        if (!async_rst_n)

          begin

             for (i=0;i<size;i=i+1) fifo_mem[i] <= 0;

             wr_ptr <= 0;

             ctr <= 0;

          end

        else

          begin

             fifo_mem[wr_ptr] <= psh_d;

             wr_ptr <= #1 wr_ptr + 1;

             ctr <= ctr + 1;

          end

     end

endmodule // generic_fifo