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+/////////////////////////////////////////////////////////////////////
+////                                                             ////
+////  WISHBONE revB.2 compliant I2C Master controller Top-level  ////
+////                                                             ////
+////                                                             ////
+////  Author: Richard Herveille                                  ////
+////          richard@asics.ws                                   ////
+////          www.asics.ws                                       ////
+////                                                             ////
+////  Downloaded from: http://www.opencores.org/projects/i2c/    ////
+////                                                             ////
+/////////////////////////////////////////////////////////////////////
+////                                                             ////
+//// Copyright (C) 2001 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.                                 ////
+////                                                             ////
+/////////////////////////////////////////////////////////////////////
+
+//  CVS Log
+//
+//  $Id: i2c_master_top.v,v 1.12 2009-01-19 20:29:26 rherveille Exp $
+//
+//  $Date: 2009-01-19 20:29:26 $
+//  $Revision: 1.12 $
+//  $Author: rherveille $
+//  $Locker:  $
+//  $State: Exp $
+//
+// Change History:
+//               Revision 1.11  2005/02/27 09:26:24  rherveille
+//               Fixed register overwrite issue.
+//               Removed full_case pragma, replaced it by a default statement.
+//
+//               Revision 1.10  2003/09/01 10:34:38  rherveille
+//               Fix a blocking vs. non-blocking error in the wb_dat output mux.
+//
+//               Revision 1.9  2003/01/09 16:44:45  rherveille
+//               Fixed a bug in the Command Register declaration.
+//
+//               Revision 1.8  2002/12/26 16:05:12  rherveille
+//               Small code simplifications
+//
+//               Revision 1.7  2002/12/26 15:02:32  rherveille
+//               Core is now a Multimaster I2C controller
+//
+//               Revision 1.6  2002/11/30 22:24:40  rherveille
+//               Cleaned up code
+//
+//               Revision 1.5  2001/11/10 10:52:55  rherveille
+//               Changed PRER reset value from 0x0000 to 0xffff, conform specs.
+//
+
+// synopsys translate_off
+`include "timescale.v"
+// synopsys translate_on
+
+`include "i2c_master_defines.v"
+
+module i2c_master_top(
+	wb_clk_i, wb_rst_i, arst_i, wb_adr_i, wb_dat_i, wb_dat_o,
+	wb_we_i, wb_stb_i, wb_cyc_i, wb_ack_o, wb_inta_o,
+	scl_pad_i, scl_pad_o, scl_padoen_o, sda_pad_i, sda_pad_o, sda_padoen_o );
+
+	// parameters
+	parameter ARST_LVL = 1'b0; // asynchronous reset level
+
+	//
+	// inputs & outputs
+	//
+
+	// wishbone signals
+	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  [7:0] wb_dat_i;     // databus input
+	output [7:0] wb_dat_o;     // databus output
+	input        wb_we_i;      // write enable input
+	input        wb_stb_i;     // stobe/core select signal
+	input        wb_cyc_i;     // valid bus cycle input
+	output       wb_ack_o;     // bus cycle acknowledge output
+	output       wb_inta_o;    // interrupt request signal output
+
+	reg [7:0] wb_dat_o;
+	reg wb_ack_o;
+	reg wb_inta_o;
+
+	// I2C signals
+	// i2c clock line
+	input  scl_pad_i;       // SCL-line input
+	output scl_pad_o;       // SCL-line output (always 1'b0)
+	output scl_padoen_o;    // SCL-line output enable (active low)
+
+	// i2c data line
+	input  sda_pad_i;       // SDA-line input
+	output sda_pad_o;       // SDA-line output (always 1'b0)
+	output sda_padoen_o;    // SDA-line output enable (active low)
+
+
+	//
+	// variable declarations
+	//
+
+	// registers
+	reg  [15:0] prer; // clock prescale register
+	reg  [ 7:0] ctr;  // control register
+	reg  [ 7:0] txr;  // transmit register
+	wire [ 7:0] rxr;  // receive register
+	reg  [ 7:0] cr;   // command register
+	wire [ 7:0] sr;   // status register
+
+	// done signal: command completed, clear command register
+	wire done;
+
+	// core enable signal
+	wire core_en;
+	wire ien;
+
+	// status register signals
+	wire irxack;
+	reg  rxack;       // received aknowledge from slave
+	reg  tip;         // transfer in progress
+	reg  irq_flag;    // interrupt pending flag
+	wire i2c_busy;    // bus busy (start signal detected)
+	wire i2c_al;      // i2c bus arbitration lost
+	reg  al;          // status register arbitration lost bit
+
+	//
+	// module body
+	//
+
+	// generate internal reset
+	wire rst_i = arst_i ^ ARST_LVL;
+
+	// generate wishbone signals
+	wire wb_wacc = wb_we_i & wb_ack_o;
+
+	// generate acknowledge output signal
+	always @(posedge wb_clk_i)
+	  wb_ack_o <= wb_cyc_i & wb_stb_i & ~wb_ack_o; // because timing is always honored
+
+	// assign DAT_O
+	always @(posedge wb_clk_i)
+	begin
+	  case (wb_adr_i) // synopsys parallel_case
+	    3'b000: wb_dat_o <= prer[ 7:0];
+	    3'b001: wb_dat_o <= prer[15:8];
+	    3'b010: wb_dat_o <= ctr;
+	    3'b011: wb_dat_o <= rxr; // write is transmit register (txr)
+	    3'b100: wb_dat_o <= sr;  // write is command register (cr)
+	    3'b101: wb_dat_o <= txr;
+	    3'b110: wb_dat_o <= cr;
+	    3'b111: wb_dat_o <= 0;   // reserved
+	    default: wb_dat_o <= 16'bx;
+	  endcase
+	end
+
+	// generate registers
+	always @(posedge wb_clk_i or negedge rst_i)
+	  if (!rst_i)
+	    begin
+	        prer <= 16'hffff;
+	        ctr  <=  8'h0;
+	        txr  <=  8'h0;
+	    end
+	  else if (wb_rst_i)
+	    begin
+	        prer <= 16'hffff;
+	        ctr  <=  8'h0;
+	        txr  <=  8'h0;
+	    end
+	  else
+	    if (wb_wacc)
+	      case (wb_adr_i) // synopsys parallel_case
+	         3'b000 : prer [ 7:0] <= wb_dat_i;
+	         3'b001 : prer [15:8] <= wb_dat_i;
+	         3'b010 : ctr         <= wb_dat_i;
+	         3'b011 : txr         <= wb_dat_i;
+	         default: ;
+	      endcase
+
+	// generate command register (special case)
+	always @(posedge wb_clk_i or negedge rst_i)
+	  if (!rst_i)
+	    cr <= 8'h0;
+	  else if (wb_rst_i)
+	    cr <= 8'h0;
+	  else if (wb_wacc)
+	    begin
+	        if (core_en & (wb_adr_i == 3'b100) )
+	          cr <= wb_dat_i;
+	    end
+	  else
+	    begin
+	        if (done | i2c_al)
+	          cr[7:4] <= 4'h0;           // clear command bits when done
+	                                        // or when aribitration lost
+	        cr[2:1] <= 2'b0;             // reserved bits
+	        cr[0]   <= 1'b0;             // clear IRQ_ACK bit
+	    end
+
+
+	// decode command register
+	wire sta  = cr[7];
+	wire sto  = cr[6];
+	wire rd   = cr[5];
+	wire wr   = cr[4];
+	wire ack  = cr[3];
+	wire iack = cr[0];
+
+	// decode control register
+	assign core_en = ctr[7];
+	assign ien = ctr[6];
+
+	// hookup byte controller block
+	i2c_master_byte_ctrl byte_controller (
+		.clk      ( wb_clk_i     ),
+		.rst      ( wb_rst_i     ),
+		.nReset   ( rst_i        ),
+		.ena      ( core_en      ),
+		.clk_cnt  ( prer         ),
+		.start    ( sta          ),
+		.stop     ( sto          ),
+		.read     ( rd           ),
+		.write    ( wr           ),
+		.ack_in   ( ack          ),
+		.din      ( txr          ),
+		.cmd_ack  ( done         ),
+		.ack_out  ( irxack       ),
+		.dout     ( rxr          ),
+		.i2c_busy ( i2c_busy     ),
+		.i2c_al   ( i2c_al       ),
+		.scl_i    ( scl_pad_i    ),
+		.scl_o    ( scl_pad_o    ),
+		.scl_oen  ( scl_padoen_o ),
+		.sda_i    ( sda_pad_i    ),
+		.sda_o    ( sda_pad_o    ),
+		.sda_oen  ( sda_padoen_o )
+	);
+
+	// status register block + interrupt request signal
+	always @(posedge wb_clk_i or negedge rst_i)
+	  if (!rst_i)
+	    begin
+	        al       <= 1'b0;
+	        rxack    <= 1'b0;
+	        tip      <= 1'b0;
+	        irq_flag <= 1'b0;
+	    end
+	  else if (wb_rst_i)
+	    begin
+	        al       <= 1'b0;
+	        rxack    <= 1'b0;
+	        tip      <= 1'b0;
+	        irq_flag <= 1'b0;
+	    end
+	  else
+	    begin
+	        al       <= i2c_al | (al & ~sta);
+	        rxack    <= irxack;
+	        tip      <= (rd | wr);
+	        irq_flag <= (done | i2c_al | irq_flag) & ~iack; // interrupt request flag is always generated
+	    end
+
+	// generate interrupt request signals
+	always @(posedge wb_clk_i or negedge rst_i)
+	  if (!rst_i)
+	    wb_inta_o <= 1'b0;
+	  else if (wb_rst_i)
+	    wb_inta_o <= 1'b0;
+	  else
+	    wb_inta_o <= irq_flag && ien; // interrupt signal is only generated when IEN (interrupt enable bit is set)
+
+	// assign status register bits
+	assign sr[7]   = rxack;
+	assign sr[6]   = i2c_busy;
+	assign sr[5]   = al;
+	assign sr[4:2] = 3'h0; // reserved
+	assign sr[1]   = tip;
+	assign sr[0]   = irq_flag;
+
+endmodule