Subversion Repositories openrisc_2011-10-31

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

///                                                               //// 

/// Wishbone arbiter, byte-wide data path, no bursting            ////

///                                                               ////

/// Simple arbiter, single master, multiple slave, for byte-wide  ////

/// peripherals                                                   ////

///                                                               ////

/// Julius Baxter, julius@opencores.org                           ////

///                                                               ////

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

////                                                              ////

//// Copyright (C) 2009, 2010 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                     ////

////                                                              ////

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

//

// Things to update when changing slave config:

//

// 1. Port list

// 2. Port specification

// 3. Slave addr select parameter

// 4. Slave addr selects

// 5. Slave input mux logic

// 6. The four different master out mux logics (dat_o mux, and ack, rty & err)

//

`include "orpsoc-defines.v"

module arbiter_bytebus

  (

   // Master in   

   wbm0_adr_o,

   wbm0_dat_o,

   wbm0_sel_o,

   wbm0_we_o,

   wbm0_cyc_o,

   wbm0_stb_o,

   wbm0_cti_o,

   wbm0_bte_o,

   wbm0_dat_i,

   wbm0_ack_i,

   wbm0_err_i,

   wbm0_rty_i,

   // Slave one

   // Wishbone Slave interface

   wbs0_adr_i,

   wbs0_dat_i,

   wbs0_we_i,

   wbs0_cyc_i,

   wbs0_stb_i,

   wbs0_cti_i,

   wbs0_bte_i,

   wbs0_dat_o,

   wbs0_ack_o,

   wbs0_err_o,

   wbs0_rty_o,

   // Slave two

   // Wishbone Slave interface

   wbs1_adr_i,

   wbs1_dat_i,

   wbs1_we_i,

   wbs1_cyc_i,

   wbs1_stb_i,

   wbs1_cti_i,

   wbs1_bte_i,

   wbs1_dat_o,

   wbs1_ack_o,

   wbs1_err_o,

   wbs1_rty_o,

   // Slave three

   // Wishbone Slave interface

   wbs2_adr_i,

   wbs2_dat_i,

   wbs2_we_i,

   wbs2_cyc_i,

   wbs2_stb_i,

   wbs2_cti_i,

   wbs2_bte_i,

   wbs2_dat_o,

   wbs2_ack_o,

   wbs2_err_o,

   wbs2_rty_o,

   // Slave four

   // Wishbone Slave interface

   wbs3_adr_i,

   wbs3_dat_i,

   wbs3_we_i,

   wbs3_cyc_i,

   wbs3_stb_i,

   wbs3_cti_i,

   wbs3_bte_i,

   wbs3_dat_o,

   wbs3_ack_o,

   wbs3_err_o,

   wbs3_rty_o,

   // Slave five

   // Wishbone Slave interface

   wbs4_adr_i,

   wbs4_dat_i,

   wbs4_we_i,

   wbs4_cyc_i,

   wbs4_stb_i,

   wbs4_cti_i,

   wbs4_bte_i,

   wbs4_dat_o,

   wbs4_ack_o,

   wbs4_err_o,

   wbs4_rty_o,

   // Slave six

   // Wishbone Slave interface

   wbs5_adr_i,

   wbs5_dat_i,

   wbs5_we_i,

   wbs5_cyc_i,

   wbs5_stb_i,

   wbs5_cti_i,

   wbs5_bte_i,

   wbs5_dat_o,

   wbs5_ack_o,

   wbs5_err_o,

   wbs5_rty_o,

   // Slave seven

   // Wishbone Slave interface

   wbs6_adr_i,

   wbs6_dat_i,

   wbs6_we_i,

   wbs6_cyc_i,

   wbs6_stb_i,

   wbs6_cti_i,

   wbs6_bte_i,

   wbs6_dat_o,

   wbs6_ack_o,

   wbs6_err_o,

   wbs6_rty_o,

   // Slave eight

   // Wishbone Slave interface

   wbs7_adr_i,

   wbs7_dat_i,

   wbs7_we_i,

   wbs7_cyc_i,

   wbs7_stb_i,

   wbs7_cti_i,

   wbs7_bte_i,

   wbs7_dat_o,

   wbs7_ack_o,

   wbs7_err_o,

   wbs7_rty_o,

   // Slave nine

   // Wishbone Slave interface

   wbs8_adr_i,

   wbs8_dat_i,

   wbs8_we_i,

   wbs8_cyc_i,

   wbs8_stb_i,

   wbs8_cti_i,

   wbs8_bte_i,

   wbs8_dat_o,

   wbs8_ack_o,

   wbs8_err_o,

   wbs8_rty_o,

   // Slave ten

   // Wishbone Slave interface

   wbs9_adr_i,

   wbs9_dat_i,

   wbs9_we_i,

   wbs9_cyc_i,

   wbs9_stb_i,

   wbs9_cti_i,

   wbs9_bte_i,

   wbs9_dat_o,

   wbs9_ack_o,

   wbs9_err_o,

   wbs9_rty_o,

   // Slave eleven

   // Wishbone Slave interface

   wbs10_adr_i,

   wbs10_dat_i,

   wbs10_we_i,

   wbs10_cyc_i,

   wbs10_stb_i,

   wbs10_cti_i,

   wbs10_bte_i,

   wbs10_dat_o,

   wbs10_ack_o,

   wbs10_err_o,

   wbs10_rty_o,

   // Slave twelve

   // Wishbone Slave interface

   wbs11_adr_i,

   wbs11_dat_i,

   wbs11_we_i,

   wbs11_cyc_i,

   wbs11_stb_i,

   wbs11_cti_i,

   wbs11_bte_i,

   wbs11_dat_o,

   wbs11_ack_o,

   wbs11_err_o,

   wbs11_rty_o,

/*

   // Slave thirteen

   // Wishbone Slave interface

   wbs12_adr_i,

   wbs12_dat_i,

   wbs12_we_i,

   wbs12_cyc_i,

   wbs12_stb_i,

   wbs12_cti_i,

   wbs12_bte_i,

   wbs12_dat_o,

   wbs12_ack_o,

   wbs12_err_o,

   wbs12_rty_o,

    // Slave fourteen

    // Wishbone Slave interface

    wbs13_adr_i,

    wbs13_dat_i,

    wbs13_we_i,

    wbs13_cyc_i,

    wbs13_stb_i,

    wbs13_cti_i,

    wbs13_bte_i,

   wbs13_dat_o,

    wbs13_ack_o,

    wbs13_err_o,

    wbs13_rty_o,

    // Slave fifteen

    // Wishbone Slave interface

    wbs14_adr_i,

    wbs14_dat_i,

    wbs14_we_i,

    wbs14_cyc_i,

    wbs14_stb_i,

    wbs14_cti_i,

    wbs14_bte_i,

   wbs14_dat_o,

    wbs14_ack_o,

    wbs14_err_o,

    wbs14_rty_o,

    // Slave sixteen

    // Wishbone Slave interface

    wbs15_adr_i,

    wbs15_dat_i,

    wbs15_we_i,

    wbs15_cyc_i,

    wbs15_stb_i,

    wbs15_cti_i,

    wbs15_bte_i,

    wbs15_dat_o,

    wbs15_ack_o,

    wbs15_err_o,

    wbs15_rty_o,

    // Slave seventeen

    // Wishbone Slave interface

    wbs16_adr_i,

    wbs16_dat_i,

    wbs16_we_i,

    wbs16_cyc_i,

    wbs16_stb_i,

    wbs16_cti_i,

    wbs16_bte_i,

    wbs16_dat_o,

    wbs16_ack_o,

    wbs16_err_o,

    wbs16_rty_o,

    // Slave eighteen

    // Wishbone Slave interface

    wbs17_adr_i,

    wbs17_dat_i,

    wbs17_we_i,

    wbs17_cyc_i,

    wbs17_stb_i,

    wbs17_cti_i,

    wbs17_bte_i,

    wbs17_dat_o,

    wbs17_ack_o,

    wbs17_err_o,

    wbs17_rty_o,

    // Slave nineteen

    // Wishbone Slave interface

    wbs18_adr_i,

    wbs18_dat_i,

    wbs18_we_i,

    wbs18_cyc_i,

    wbs18_stb_i,

    wbs18_cti_i,

    wbs18_bte_i,

    wbs18_dat_o,

    wbs18_ack_o,

    wbs18_err_o,

    wbs18_rty_o,

    // Slave twenty

    // Wishbone Slave interface

    wbs19_adr_i,

    wbs19_dat_i,

    wbs19_we_i,

    wbs19_cyc_i,

    wbs19_stb_i,

    wbs19_cti_i,

    wbs19_bte_i,

    wbs19_dat_o,

    wbs19_ack_o,

    wbs19_err_o,

    wbs19_rty_o,

    */

   wb_clk, wb_rst

   );

   parameter wb_dat_width = 32;

   parameter wbs_dat_width = 8;

   parameter wb_adr_width = 32;

   parameter wb_addr_match_width = 8;

   parameter wb_num_slaves = 20; // Currently can handle up to 20

   // Slave addresses

   parameter slave0_adr =  8'h00;

   parameter slave1_adr =  8'h00;

   parameter slave2_adr =  8'h00;

   parameter slave3_adr =  8'h00;

   parameter slave4_adr =  8'h00;

   parameter slave5_adr =  8'h00;

   parameter slave6_adr =  8'h00;

   parameter slave7_adr =  8'h00;

   parameter slave8_adr =  8'h00;

   parameter slave9_adr =  8'h00;

   parameter slave10_adr = 8'h00;

   parameter slave11_adr = 8'h00;

   parameter slave12_adr = 8'h00;

   parameter slave13_adr = 8'h00;

   parameter slave14_adr = 8'h00;

   parameter slave15_adr = 8'h00;

   parameter slave16_adr = 8'h00;

   parameter slave17_adr = 8'h00;

   parameter slave18_adr = 8'h00;

   parameter slave19_adr = 8'h00;

`define WB_ARB_ADDR_MATCH_SEL wb_adr_width-1:wb_adr_width-wb_addr_match_width

   input wb_clk;

   input wb_rst;

   // WB Master one

   input [wb_adr_width-1:0] wbm0_adr_o;

   input [wb_dat_width-1:0] wbm0_dat_o;

   input [3:0]               wbm0_sel_o;

   input                    wbm0_we_o;

   input                    wbm0_cyc_o;

   input                    wbm0_stb_o;

   input [2:0]               wbm0_cti_o;

   input [1:0]               wbm0_bte_o;

   output [wb_dat_width-1:0] wbm0_dat_i;

   output                    wbm0_ack_i;

   output                    wbm0_err_i;

   output                    wbm0_rty_i;

   // Slave one

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs0_adr_i;

   output [wbs_dat_width-1:0] wbs0_dat_i;

   output                    wbs0_we_i;

   output                    wbs0_cyc_i;

   output                    wbs0_stb_i;

   output [2:0]       wbs0_cti_i;

   output [1:0]       wbs0_bte_i;

   input [wbs_dat_width-1:0]  wbs0_dat_o;

   input                     wbs0_ack_o;

   input                     wbs0_err_o;

   input                     wbs0_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs1_adr_i;

   output [wbs_dat_width-1:0] wbs1_dat_i;

   output                    wbs1_we_i;

   output                    wbs1_cyc_i;

   output                    wbs1_stb_i;

   output [2:0]       wbs1_cti_i;

   output [1:0]       wbs1_bte_i;

   input [wbs_dat_width-1:0]  wbs1_dat_o;

   input                     wbs1_ack_o;

   input                     wbs1_err_o;

   input                     wbs1_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs2_adr_i;

   output [wbs_dat_width-1:0] wbs2_dat_i;

   output                    wbs2_we_i;

   output                    wbs2_cyc_i;

   output                    wbs2_stb_i;

   output [2:0]       wbs2_cti_i;

   output [1:0]       wbs2_bte_i;

   input [wbs_dat_width-1:0]  wbs2_dat_o;

   input                     wbs2_ack_o;

   input                     wbs2_err_o;

   input                     wbs2_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs3_adr_i;

   output [wbs_dat_width-1:0] wbs3_dat_i;

   output                    wbs3_we_i;

   output                    wbs3_cyc_i;

   output                    wbs3_stb_i;

   output [2:0]       wbs3_cti_i;

   output [1:0]       wbs3_bte_i;

   input [wbs_dat_width-1:0]  wbs3_dat_o;

   input                     wbs3_ack_o;

   input                     wbs3_err_o;

   input                     wbs3_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs4_adr_i;

   output [wbs_dat_width-1:0] wbs4_dat_i;

   output                    wbs4_we_i;

   output                    wbs4_cyc_i;

   output                    wbs4_stb_i;

   output [2:0]       wbs4_cti_i;

   output [1:0]       wbs4_bte_i;

   input [wbs_dat_width-1:0]  wbs4_dat_o;

   input                     wbs4_ack_o;

   input                     wbs4_err_o;

   input                     wbs4_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs5_adr_i;

   output [wbs_dat_width-1:0] wbs5_dat_i;

   output                    wbs5_we_i;

   output                    wbs5_cyc_i;

   output                    wbs5_stb_i;

   output [2:0]       wbs5_cti_i;

   output [1:0]       wbs5_bte_i;

   input [wbs_dat_width-1:0]  wbs5_dat_o;

   input                     wbs5_ack_o;

   input                     wbs5_err_o;

   input                     wbs5_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs6_adr_i;

   output [wbs_dat_width-1:0] wbs6_dat_i;

   output                    wbs6_we_i;

   output                    wbs6_cyc_i;

   output                    wbs6_stb_i;

   output [2:0]       wbs6_cti_i;

   output [1:0]       wbs6_bte_i;

   input [wbs_dat_width-1:0]  wbs6_dat_o;

   input                     wbs6_ack_o;

   input                     wbs6_err_o;

   input                     wbs6_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs7_adr_i;

   output [wbs_dat_width-1:0] wbs7_dat_i;

   output                    wbs7_we_i;

   output                    wbs7_cyc_i;

   output                    wbs7_stb_i;

   output [2:0]       wbs7_cti_i;

   output [1:0]       wbs7_bte_i;

   input [wbs_dat_width-1:0]  wbs7_dat_o;

   input                     wbs7_ack_o;

   input                     wbs7_err_o;

   input                     wbs7_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs8_adr_i;

   output [wbs_dat_width-1:0] wbs8_dat_i;

   output                    wbs8_we_i;

   output                    wbs8_cyc_i;

   output                    wbs8_stb_i;

   output [2:0]       wbs8_cti_i;

   output [1:0]       wbs8_bte_i;

   input [wbs_dat_width-1:0]  wbs8_dat_o;

   input                     wbs8_ack_o;

   input                     wbs8_err_o;

   input                     wbs8_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs9_adr_i;

   output [wbs_dat_width-1:0] wbs9_dat_i;

   output                    wbs9_we_i;

   output                    wbs9_cyc_i;

   output                    wbs9_stb_i;

   output [2:0]       wbs9_cti_i;

   output [1:0]       wbs9_bte_i;

   input [wbs_dat_width-1:0]  wbs9_dat_o;

   input                     wbs9_ack_o;

   input                     wbs9_err_o;

   input                     wbs9_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs10_adr_i;

   output [wbs_dat_width-1:0] wbs10_dat_i;

   output                    wbs10_we_i;

   output                    wbs10_cyc_i;

   output                    wbs10_stb_i;

   output [2:0]       wbs10_cti_i;

   output [1:0]       wbs10_bte_i;

   input [wbs_dat_width-1:0]  wbs10_dat_o;

   input                     wbs10_ack_o;

   input                     wbs10_err_o;

   input                     wbs10_rty_o;

 // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs11_adr_i;

   output [wbs_dat_width-1:0] wbs11_dat_i;

   output                    wbs11_we_i;

   output                    wbs11_cyc_i;

   output                    wbs11_stb_i;

   output [2:0]       wbs11_cti_i;

   output [1:0]       wbs11_bte_i;

   input [wbs_dat_width-1:0]  wbs11_dat_o;

   input                     wbs11_ack_o;

   input                     wbs11_err_o;

   input                     wbs11_rty_o;

/*

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs12_adr_i;

   output [wbs_dat_width-1:0] wbs12_dat_i;

   output                     wbs12_we_i;

   output                     wbs12_cyc_i;

   output                     wbs12_stb_i;

   output [2:0]               wbs12_cti_i;

   output [1:0]               wbs12_bte_i;

   input [wbs_dat_width-1:0]  wbs12_dat_o;

   input                      wbs12_ack_o;

   input                      wbs12_err_o;

   input                      wbs12_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs13_adr_i;

   output [wbs_dat_width-1:0] wbs13_dat_i;

   output                    wbs13_we_i;

   output                    wbs13_cyc_i;

   output                    wbs13_stb_i;

   output [2:0]              wbs13_cti_i;

   output [1:0]              wbs13_bte_i;

   input [wbs_dat_width-1:0]  wbs13_dat_o;

   input                     wbs13_ack_o;

   input                     wbs13_err_o;

   input                     wbs13_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs14_adr_i;

   output [wbs_dat_width-1:0] wbs14_dat_i;

   output                    wbs14_we_i;

   output                    wbs14_cyc_i;

   output                    wbs14_stb_i;

   output [2:0]              wbs14_cti_i;

   output [1:0]              wbs14_bte_i;

   input [wbs_dat_width-1:0]  wbs14_dat_o;

   input                     wbs14_ack_o;

   input                     wbs14_err_o;

   input                     wbs14_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs15_adr_i;

   output [wbs_dat_width-1:0] wbs15_dat_i;

   output                    wbs15_we_i;

   output                    wbs15_cyc_i;

   output                    wbs15_stb_i;

   output [2:0]              wbs15_cti_i;

   output [1:0]              wbs15_bte_i;

   input [wbs_dat_width-1:0]  wbs15_dat_o;

   input                     wbs15_ack_o;

   input                     wbs15_err_o;

   input                     wbs15_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs16_adr_i;

   output [wbs_dat_width-1:0] wbs16_dat_i;

   output                    wbs16_we_i;

   output                    wbs16_cyc_i;

   output                    wbs16_stb_i;

   output [2:0]              wbs16_cti_i;

   output [1:0]              wbs16_bte_i;

   input [wbs_dat_width-1:0]  wbs16_dat_o;

   input                     wbs16_ack_o;

   input                     wbs16_err_o;

   input                     wbs16_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs17_adr_i;

   output [wbs_dat_width-1:0] wbs17_dat_i;

   output                    wbs17_we_i;

   output                    wbs17_cyc_i;

   output                    wbs17_stb_i;

   output [2:0]              wbs17_cti_i;

   output [1:0]              wbs17_bte_i;

   input [wbs_dat_width-1:0]  wbs17_dat_o;

   input                     wbs17_ack_o;

   input                     wbs17_err_o;

   input                     wbs17_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs18_adr_i;

   output [wbs_dat_width-1:0] wbs18_dat_i;

   output                    wbs18_we_i;

   output                    wbs18_cyc_i;

   output                    wbs18_stb_i;

   output [2:0]              wbs18_cti_i;

   output [1:0]              wbs18_bte_i;

   input [wbs_dat_width-1:0]  wbs18_dat_o;

   input                     wbs18_ack_o;

   input                     wbs18_err_o;

   input                     wbs18_rty_o;

   // Wishbone Slave interface

   output [wb_adr_width-1:0] wbs19_adr_i;

   output [wbs_dat_width-1:0] wbs19_dat_i;

   output                    wbs19_we_i;

   output                    wbs19_cyc_i;

   output                    wbs19_stb_i;

   output [2:0]              wbs19_cti_i;

   output [1:0]              wbs19_bte_i;

   input [wbs_dat_width-1:0]  wbs19_dat_o;

   input                     wbs19_ack_o;

   input                     wbs19_err_o;

   input                     wbs19_rty_o;

 */

   reg               watchdog_err;

   // Master input mux output wires

   wire [wb_adr_width-1:0]   wbm_adr_o;

   wire [wbs_dat_width-1:0]  wbm_dat_o;

   wire [3:0]                 wbm_sel_o;

   wire                      wbm_we_o;

   wire                      wbm_cyc_o;

   wire                      wbm_stb_o;

   wire [2:0]                 wbm_cti_o;

   wire [1:0]                 wbm_bte_o;

   wire [wbs_dat_width-1:0]   wbm_dat_byte_i;

   wire                      wbm_ack_i;

   wire                      wbm_err_i;

   wire                      wbm_rty_i;

   // Master input mux (not really used, only one master on this bus)

   assign wbm_adr_o = wbm0_adr_o;

   // Select the right byte and put it on the data out line

   // !BIG ENDIAN!

   assign wbm_dat_o = wbm0_sel_o[3] ? wbm0_dat_o[31:24] :

                      wbm0_sel_o[2] ? wbm0_dat_o[23:16] :

                      wbm0_sel_o[1] ? wbm0_dat_o[15:8] :

                      wbm0_dat_o[7:0];

   assign wbm_we_o = wbm0_we_o;

   assign wbm_cyc_o = wbm0_stb_o;

   assign wbm_stb_o = wbm0_stb_o;

   // Will we really need these for byte-peripherals

   assign wbm_cti_o = wbm0_cti_o;

   assign wbm_bte_o = wbm0_bte_o;

   // Signals back to the master

   assign wbm0_dat_i = (wbm0_sel_o[3]) ? {wbm_dat_byte_i, 24'd0} :

                       (wbm0_sel_o[2]) ? {8'd0, wbm_dat_byte_i, 16'd0} :

                       (wbm0_sel_o[1]) ? {16'd0, wbm_dat_byte_i, 8'd0} :

                       {24'd0, wbm_dat_byte_i};

   assign wbm0_ack_i = wbm_ack_i;

   assign wbm0_err_i = wbm_err_i;

   assign wbm0_rty_i = wbm_rty_i;

`ifdef ARBITER_BYTEBUS_WATCHDOG

   reg [`ARBITER_BYTEBUS_WATCHDOG_TIMER_WIDTH:0] watchdog_timer;

   reg                       wbm_stb_r; // Register strobe

   wire                      wbm_stb_edge; // Detect its edge

   always @(posedge wb_clk)

     wbm_stb_r <= wbm_stb_o;

   assign wbm_stb_edge = (wbm_stb_o & !wbm_stb_r);

   // Counter logic

   always @(posedge wb_clk)

     if (wb_rst) watchdog_timer <= 0;

     else if (wbm_ack_i) // When we see an ack, turn off timer

       watchdog_timer <= 0;

     else if (wbm_stb_edge) // New access means start timer again

       watchdog_timer <= 1;

     else if (|watchdog_timer) // Continue counting if counter > 0

       watchdog_timer <= watchdog_timer + 1;

   always @(posedge wb_clk)