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

//

//  WISHBONE revB.2 compliant Programable Interrupt Timer - Bus interface

//

//  Author: Bob Hayes

//          rehayes@opencores.org

//

//  Downloaded from: http://www.opencores.org/projects/pit.....

//

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

// Copyright (c) 2009, Robert Hayes

//

// All rights reserved.

//

// Redistribution and use in source and binary forms, with or without

// modification, are permitted provided that the following conditions are met:

//     * Redistributions of source code must retain the above copyright

//       notice, this list of conditions and the following disclaimer.

//     * Redistributions in binary form must reproduce the above copyright

//       notice, this list of conditions and the following disclaimer in the

//       documentation and/or other materials provided with the distribution.

//     * Neither the name of the <organization> nor the

//       names of its contributors may be used to endorse or promote products

//       derived from this software without specific prior written permission.

//

// THIS SOFTWARE IS PROVIDED BY Robert Hayes ''AS IS'' AND ANY

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

// WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE

// DISCLAIMED. IN NO EVENT SHALL Robert Hayes 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.

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

// 45678901234567890123456789012345678901234567890123456789012345678901234567890

module pit_wb_bus #(parameter ARST_LVL = 1'b0,    // asynchronous reset level

                    parameter DWIDTH = 16,

                    parameter SINGLE_CYCLE = 1'b0)

  (

  // Wishbone Signals

  output reg  [DWIDTH-1:0] wb_dat_o,     // databus output - Pseudo Register

  output                   wb_ack_o,     // bus cycle acknowledge output

  input                    wb_clk_i,     // master clock input

  input                    wb_rst_i,     // synchronous active high reset

  input                    arst_i,       // asynchronous reset

  input             [ 2:0] wb_adr_i,     // lower address bits

  input       [DWIDTH-1:0] wb_dat_i,     // databus input

  input                    wb_we_i,      // write enable input

  input                    wb_stb_i,     // stobe/core select signal

  input                    wb_cyc_i,     // valid bus cycle input

  input              [1:0] wb_sel_i,     // Select byte in word bus transaction

  // PIT Control Signals

  output reg        [ 3:0] write_regs,   // Decode write control register

  output                   async_rst_b,  //

  output                   sync_reset,   //

  input                    irq_source,   //

  input             [47:0] read_regs     // status register bits

  );

  // registers

  reg        bus_wait_state;  // Holdoff wb_ack_o for one clock to add wait state

  reg  [2:0] addr_latch;      // Capture WISHBONE Address 

  // Wires

  wire       eight_bit_bus;

  wire       module_sel;      // This module is selected for bus transaction

  wire       wb_wacc;         // WISHBONE Write Strobe

  wire       wb_racc;         // WISHBONE Read Access (Clock gating signal)

  wire [2:0] address;         // Select either direct or latched address

  //

  // module body

  //

  // generate internal resets

  assign eight_bit_bus = (DWIDTH == 8);

  assign async_rst_b = arst_i ^ ARST_LVL;

  assign sync_reset = wb_rst_i;

  // generate wishbone signals

  assign module_sel = wb_cyc_i && wb_stb_i;

  assign wb_wacc    = module_sel && wb_we_i && (wb_ack_o || SINGLE_CYCLE);

  assign wb_racc    = module_sel && !wb_we_i;

  assign wb_ack_o   = SINGLE_CYCLE ? module_sel : (bus_wait_state && module_sel);

  assign address    = SINGLE_CYCLE ? wb_adr_i : addr_latch;

  // generate acknowledge output signal, By using register all accesses takes two cycles.

  //  Accesses in back to back clock cycles are not possable.

  always @(posedge wb_clk_i or negedge async_rst_b)

    if (!async_rst_b)

      bus_wait_state <=  1'b0;

    else if (sync_reset)

      bus_wait_state <=  1'b0;

    else

      bus_wait_state <=  module_sel && !bus_wait_state;

  // Capture address in first cycle of WISHBONE Bus tranaction

  //  Only used when Wait states are enabled

  always @(posedge wb_clk_i)

    if ( module_sel )                  // Clock gate for power saving

      addr_latch <= wb_adr_i;

  // WISHBONE Read Data Mux

  always @*

      case ({eight_bit_bus, address}) // synopsys parallel_case

      // 8 bit Bus, 8 bit Granularity

      4'b1_000: wb_dat_o = read_regs[ 7: 0];  // 8 bit read address 0

      4'b1_001: wb_dat_o = read_regs[15: 8];  // 8 bit read address 1

      4'b1_010: wb_dat_o = read_regs[23:16];  // 8 bit read address 2

      4'b1_011: wb_dat_o = read_regs[31:24];  // 8 bit read address 3

      4'b1_100: wb_dat_o = read_regs[39:32];  // 8 bit read address 4

      4'b1_101: wb_dat_o = read_regs[47:40];  // 8 bit read address 5

      // 16 bit Bus, 16 bit Granularity

      4'b0_000: wb_dat_o = read_regs[15: 0];  // 16 bit read access address 0

      4'b0_001: wb_dat_o = read_regs[31:16];

      4'b0_010: wb_dat_o = read_regs[47:32];

    endcase

  // generate wishbone write register strobes -- one hot if 8 bit bus

  always @*

    begin

      write_regs = 0;

      if (wb_wacc)

        case ({eight_bit_bus, address}) // synopsys parallel_case

           // 8 bit Bus, 8 bit Granularity

           4'b1_000 : write_regs = 4'b0001;

           4'b1_001 : write_regs = 4'b0010;

           4'b1_010 : write_regs = 4'b0100;

           4'b1_011 : write_regs = 4'b1000;

           // 16 bit Bus, 16 bit Granularity

           4'b0_000 : write_regs = 4'b0011;

           4'b0_001 : write_regs = 4'b1100;

           default: ;

        endcase

    end

endmodule  // pit_wb_bus