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

////                                                             ////

////  OpenCores                    MC68HC11E based SPI interface ////

////                                                             ////

////  Author: Richard Herveille                                  ////

////          richard@asics.ws                                   ////

////          www.asics.ws                                       ////

////                                                             ////

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

////                                                             ////

//// Copyright (C) 2002 Richard Herveille                        ////

////                    richard@asics.ws                         ////

////                                                             ////

//// 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 SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY     ////

//// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED   ////

//// TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS   ////

//// FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL THE AUTHOR      ////

//// OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,         ////

//// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES    ////

//// (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE   ////

//// GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR        ////

//// BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF  ////

//// LIABILITY, WHETHER IN  CONTRACT, STRICT LIABILITY, OR TORT  ////

//// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT  ////

//// OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE         ////

//// POSSIBILITY OF SUCH DAMAGE.                                 ////

////                                                             ////

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

//

// Motorola MC68HC11E based SPI interface

//

// Currently only MASTER mode is supported

//

// synopsys translate_off

`include "timescale.v"

// synopsys translate_on

`define SIMPLE_SPI_RST_SENS rst_i

//module simple_spi_top(

module simple_spi ( // renamed by Julius

                    // 8bit WISHBONE bus slave interface

                    clk_i,         // clock

                    rst_i,         // reset (asynchronous active low)

                    cyc_i,         // cycle

                    stb_i,         // strobe

                    adr_i,         // address

                    we_i,          // write enable

                    dat_i,         // data input

                    dat_o,         // data output

                    ack_o,         // normal bus termination

                    inta_o,        // interrupt output

                    sck_o,         // serial clock output

                    ss_o, //slave select

                    mosi_o,        // MasterOut SlaveIN

                    miso_i         // MasterIn SlaveOut             

                    );

   parameter slave_select_width = 1;

   input  wire      clk_i;         // clock

   input  wire      rst_i;         // reset (asynchronous active low)

   input  wire      cyc_i;         // cycle

   input  wire      stb_i;         // strobe

   input  wire [2:0] adr_i;         // address

   input  wire       we_i;          // write enable

   input  wire [7:0] dat_i;         // data input

   output reg [7:0]  dat_o;         // data output

   output reg        ack_o;         // normal bus termination

   output reg        inta_o;        // interrupt output

   // SPI port

   output reg        sck_o;         // serial clock output

   output [slave_select_width-1:0] ss_o;

   output wire                         mosi_o;        // MasterOut SlaveIN

   input  wire                         miso_i;         // MasterIn SlaveOut     

   reg [slave_select_width-1:0]        ss_r;

  //

  // Module body

  //

  reg  [7:0] spcr;       // Serial Peripheral Control Register ('HC11 naming)

  wire [7:0] spsr;       // Serial Peripheral Status register ('HC11 naming)

  reg  [7:0] sper;       // Serial Peripheral Extension register

  reg  [7:0] treg; // Transmit/Receive register

  // fifo signals

  wire [7:0] rfdout;

  reg        wfre, rfwe;

  wire       rfre, rffull, rfempty;

  wire [7:0] wfdout;

  wire       wfwe, wffull, wfempty;

  // misc signals

  wire      tirq;     // transfer interrupt (selected number of transfers done)

  wire      wfov;     // write fifo overrun (writing while fifo full)

  reg [1:0] state;    // statemachine state

  reg [2:0] bcnt;

  //

  // Wishbone interface

  wire wb_acc = cyc_i & stb_i;       // WISHBONE access

  wire wb_wr  = wb_acc & we_i;       // WISHBONE write access

  // dat_i

  always @(posedge clk_i)

    if (`SIMPLE_SPI_RST_SENS)

      begin

         spcr <=  8'h10;  // set master bit

         sper <=  8'h00;

         ss_r <=  0;

      end

    else if (wb_wr)

      begin

        if (adr_i == 3'b000)

          spcr <=  dat_i | 8'h10; // always set master bit

        if (adr_i == 3'b011)

          sper <=  dat_i;

         if (adr_i == 3'b100)

           ss_r <=  dat_i[slave_select_width-1:0];

      end // if (wb_wr)

   // Slave select output

   // SPI slave select is active low   

   assign ss_o = ~ss_r;

  // write fifo

  assign wfwe = wb_acc & (adr_i == 3'b010) & ack_o &  we_i;

  assign wfov = wfwe & wffull;

  // dat_o

  always @(posedge clk_i)

    case(adr_i) // synopsys full_case parallel_case

      3'b000: dat_o <=  spcr;

      3'b001: dat_o <=  spsr;

      3'b010: dat_o <=  rfdout;

      3'b011: dat_o <=  sper;

      3'b100: dat_o <=  {{(8-slave_select_width){1'b0}},ss_r};

      default:

        dat_o <= 0;

    endcase

  // read fifo

  assign rfre = wb_acc & (adr_i == 3'b010) & ack_o & ~we_i;

  // ack_o

  always @(posedge clk_i)

    if (`SIMPLE_SPI_RST_SENS)

      ack_o <=  1'b0;

    else

      ack_o <=  wb_acc & !ack_o;

  // decode Serial Peripheral Control Register

  wire       spie = spcr[7];   // Interrupt enable bit

  wire       spe  = spcr[6];   // System Enable bit

  wire       dwom = spcr[5];   // Port D Wired-OR Mode Bit

  wire       mstr = spcr[4];   // Master Mode Select Bit

  wire       cpol = spcr[3];   // Clock Polarity Bit

  wire       cpha = spcr[2];   // Clock Phase Bit

  wire [1:0] spr  = spcr[1:0]; // Clock Rate Select Bits

  // decode Serial Peripheral Extension Register

  wire [1:0] icnt = sper[7:6]; // interrupt on transfer count

  wire [1:0] spre = sper[1:0]; // extended clock rate select

  wire [3:0] espr = {spre, spr};

  // generate status register

  wire wr_spsr = wb_wr & (adr_i == 3'b001);

  reg spif;

  always @(posedge clk_i)

    if (~spe | rst_i)

      spif <=  1'b0;

    else

      spif <=  (tirq | spif) & ~(wr_spsr & dat_i[7]);

  reg wcol;

  always @(posedge clk_i)

    if (~spe | rst_i)

      wcol <=  1'b0;

    else

      wcol <=  (wfov | wcol) & ~(wr_spsr & dat_i[6]);

  assign spsr[7]   = spif;

  assign spsr[6]   = wcol;

  assign spsr[5:4] = 2'b00;

  assign spsr[3]   = wffull;

  assign spsr[2]   = wfempty;

  assign spsr[1]   = rffull;

  assign spsr[0]   = rfempty;

  // generate IRQ output (inta_o)

  always @(posedge clk_i)

    inta_o <=  spif & spie;

   wire [7:0] wfifo_dat_i;

   assign wfifo_dat_i = dat_i;

   wire       wfifo_wfwe;

   assign wfifo_wfwe =  wfwe;

   wire       rfifo_rfre = rfre;

  //

  // hookup read/write buffer fifo

  fifo4 #(8)

  rfifo(

        .clk   ( clk_i   ),

        .rst   ( ~rst_i   ),

        .clr   ( ~spe    ),

        .din   ( treg    ),

        .we    ( rfwe    ),

        .dout  ( rfdout  ),

        .re    ( rfifo_rfre    ),

        .full  ( rffull  ),

        .empty ( rfempty )

  ),

  wfifo(

        .clk   ( clk_i   ),

        .rst   ( ~rst_i   ),

        .clr   ( ~spe    ),

        .din   ( wfifo_dat_i   ),

        .we    ( wfifo_wfwe    ),

        .dout  ( wfdout  ),

        .re    ( wfre    ),

        .full  ( wffull  ),

        .empty ( wfempty )

  );

  //

  // generate clk divider

  reg [11:0] clkcnt;

  always @(posedge clk_i)

    if(spe & (|clkcnt & |state))

      clkcnt <=  clkcnt - 11'h1;

    else

      case (espr) // synopsys full_case parallel_case

        4'b0000: clkcnt <=  12'h0;   // 2   -- original M68HC11 coding

        4'b0001: clkcnt <=  12'h1;   // 4   -- original M68HC11 coding

        4'b0010: clkcnt <=  12'h3;   // 16  -- original M68HC11 coding

        4'b0011: clkcnt <=  12'hf;   // 32  -- original M68HC11 coding

        4'b0100: clkcnt <=  12'h1f;  // 8

        4'b0101: clkcnt <=  12'h7;   // 64

        4'b0110: clkcnt <=  12'h3f;  // 128

        4'b0111: clkcnt <=  12'h7f;  // 256

        4'b1000: clkcnt <=  12'hff;  // 512

        4'b1001: clkcnt <=  12'h1ff; // 1024

        4'b1010: clkcnt <=  12'h3ff; // 2048

        4'b1011: clkcnt <=  12'h7ff; // 4096

      endcase

  // generate clock enable signal

  wire ena = ~|clkcnt;

  // transfer statemachine

  always @(posedge clk_i)

    if (~spe | rst_i)

      begin

          state <=  2'b00; // idle

          bcnt  <=  3'h0;

          treg  <=  8'h00;

          wfre  <=  1'b0;

          rfwe  <=  1'b0;

          sck_o <=  1'b0;

      end

    else

      begin

         wfre <=  1'b0;

         rfwe <=  1'b0;

         case (state) //synopsys full_case parallel_case

           2'b00: // idle state

              begin

                  bcnt  <=  3'h7;   // set transfer counter

                  treg  <=  wfdout; // load transfer register

                  sck_o <=  cpol;   // set sck

                  if (~wfempty) begin

                    wfre  <=  1'b1;

                    state <=  2'b01;

                    if (cpha) sck_o <=  ~sck_o;

                  end

              end

           2'b01: // clock-phase2, next data

              if (ena) begin

                sck_o   <=  ~sck_o;

                state   <=  2'b11;

              end

           2'b11: // clock phase1

              if (ena) begin

                treg <=  {treg[6:0], miso_i};

                bcnt <=  bcnt -3'h1;

                if (~|bcnt) begin

                  state <=  2'b00;

                  sck_o <=  cpol;

                  rfwe  <=  1'b1;

                end else begin

                  state <=  2'b01;

                  sck_o <=  ~sck_o;

                end

              end

           2'b10: state <=  2'b00;

         endcase

      end

  assign mosi_o = treg[7];

  // count number of transfers (for interrupt generation)

  reg [1:0] tcnt; // transfer count

  always @(posedge clk_i)

    if (~spe)

      tcnt <=  icnt;

    else if (rfwe) // rfwe gets asserted when all bits have been transfered

      if (|tcnt)

        tcnt <=  tcnt - 2'h1;

      else

        tcnt <=  icnt;

  assign tirq = ~|tcnt & rfwe;

endmodule