//////////////////////////////////////////////////////////////////////
////                                                              ////
//// i2cSlave.v                                                   ////
////                                                              ////
//// This file is part of the i2cSlave opencores effort.
//// <http://www.opencores.org/cores//>                           ////
////                                                              ////
//// Module Description:                                          ////
//// You will need to modify this file to implement your 
//// interface.
////                                                              ////
//// To Do:                                                       ////
//// 
////                                                              ////
//// Author(s):                                                   ////
//// - Steve Fielding, sfielding@base2designs.com                 ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
////                                                              ////
//// Copyright (C) 2008 Steve Fielding 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>                   ////
////                                                              ////
//////////////////////////////////////////////////////////////////////
//
`include "i2cSlave_define.v"


module i2cSlave (
  clk,
  rst,
  sda,
  scl,
  tb_readEn,
  tb_writeEn,
  tb_addr,
  tb_dataIn,
  tb_dataOut
);

input clk;
input rst;
inout sda;
input scl;

// tb interface
input tb_readEn;
input tb_writeEn;
input [15:0] tb_addr;
input [15:0] tb_dataIn;
output [15:0] tb_dataOut;

// local wires and regs
reg sdaDeb;
reg sclDeb;
reg [`DEB_I2C_LEN-1:0] sdaPipe;
reg [`DEB_I2C_LEN-1:0] sclPipe;

reg [`SCL_DEL_LEN-1:0] sclDelayed;
reg [`SDA_DEL_LEN-1:0] sdaDelayed;
reg [1:0] startStopDetState;
wire clearStartStopDet;
wire sdaOut;
wire sdaIn;
wire [15:0] regAddr;
wire [7:0] dataToRegIF;
wire writeEn;
wire [7:0] dataFromRegIF;
reg [1:0] rstPipe;
wire rstSyncToClk;
reg startEdgeDet;

assign sda = (sdaOut == 1'b0) ? 1'b0 : 1'bz;
assign sdaIn = sda;

// sync rst rsing edge to clk
always @(posedge clk) begin
  if (rst == 1'b1)
    rstPipe <= 2'b11;
  else
    rstPipe <= {rstPipe[0], 1'b0};
end

assign rstSyncToClk = rstPipe[1];

// debounce sda and scl
always @(posedge clk) begin
  if (rstSyncToClk == 1'b1) begin
    sdaPipe <= {`DEB_I2C_LEN{1'b1}};
    sdaDeb <= 1'b1;
    sclPipe <= {`DEB_I2C_LEN{1'b1}};
    sclDeb <= 1'b1;
  end
  else begin
    sdaPipe <= {sdaPipe[`DEB_I2C_LEN-2:0], sdaIn};
    sclPipe <= {sclPipe[`DEB_I2C_LEN-2:0], scl};
    if (&sclPipe[`DEB_I2C_LEN-1:1] == 1'b1)
      sclDeb <= 1'b1;
    else if (|sclPipe[`DEB_I2C_LEN-1:1] == 1'b0)
      sclDeb <= 1'b0;
    if (&sdaPipe[`DEB_I2C_LEN-1:1] == 1'b1)
      sdaDeb <= 1'b1;
    else if (|sdaPipe[`DEB_I2C_LEN-1:1] == 1'b0)
      sdaDeb <= 1'b0;
  end
end


// delay scl and sda
// sclDelayed is used as a delayed sampling clock
// sdaDelayed is only used for start stop detection
// Because sda hold time from scl falling is 0nS
// sda must be delayed with respect to scl to avoid incorrect
// detection of start/stop at scl falling edge. 
always @(posedge clk) begin
  if (rstSyncToClk == 1'b1) begin
    sclDelayed <= {`SCL_DEL_LEN{1'b1}};
    sdaDelayed <= {`SDA_DEL_LEN{1'b1}};
  end
  else begin
    sclDelayed <= {sclDelayed[`SCL_DEL_LEN-2:0], sclDeb};
    sdaDelayed <= {sdaDelayed[`SDA_DEL_LEN-2:0], sdaDeb};
  end
end

// start stop detection
always @(posedge clk) begin
  if (rstSyncToClk == 1'b1) begin
    startStopDetState <= `NULL_DET;
    startEdgeDet <= 1'b0;
  end
  else begin
    if (sclDeb == 1'b1 && sdaDelayed[`SDA_DEL_LEN-2] == 1'b0 && sdaDelayed[`SDA_DEL_LEN-1] == 1'b1)
      startEdgeDet <= 1'b1;
    else
      startEdgeDet <= 1'b0;
    if (clearStartStopDet == 1'b1)
      startStopDetState <= `NULL_DET;
    else if (sclDeb == 1'b1) begin
      if (sdaDelayed[`SDA_DEL_LEN-2] == 1'b1 && sdaDelayed[`SDA_DEL_LEN-1] == 1'b0) 
        startStopDetState <= `STOP_DET;
      else if (sdaDelayed[`SDA_DEL_LEN-2] == 1'b0 && sdaDelayed[`SDA_DEL_LEN-1] == 1'b1)
        startStopDetState <= `START_DET;
    end
  end
end


registerInterface u_registerInterface(
  .clk(clk),
  .addr(regAddr),
  .dataIn(dataToRegIF),
  .writeEn(writeEn),
  .dataOut(dataFromRegIF),
  .tb_readEn(tb_readEn),
  .tb_writeEn(tb_writeEn),
  .tb_addr(tb_addr),
  .tb_dataIn(tb_dataIn),
  .tb_dataOut(tb_dataOut)
);

serialInterface u_serialInterface (
  .clk(clk), 
  .rst(rstSyncToClk | startEdgeDet), 
  .dataIn(dataFromRegIF), 
  .dataOut(dataToRegIF), 
  .writeEn(writeEn),
  .regAddr(regAddr), 
  .scl(sclDelayed[`SCL_DEL_LEN-1]), 
  .sdaIn(sdaDeb), 
  .sdaOut(sdaOut), 
  .startStopDetState(startStopDetState),
  .clearStartStopDet(clearStartStopDet) 
);


endmodule