//////////////////////////////////////////////////////////////////////////////
//
//  Xilinx, Inc. 2008                 www.xilinx.com
//
//////////////////////////////////////////////////////////////////////////////
//
//  File name :       encode.v
//
//  Description :     TMDS encoder  
//
//  Date - revision : Jan. 2008 - v 1.0
//
//  Author :          Bob Feng
//
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//  Copyright © 2006 Xilinx, Inc.
//  All rights reserved
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//////////////////////////////////////////////////////////////////////////////  
// Modifications copyright (c) 2011, Andrew "bunnie" Huang
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//////////////////////////////////////////////////////////////////////////////
`timescale 1 ps / 1ps

module encoder (
  input            clkin,    // pixel clock input
  input            rstin,    // async. reset input (active high)
  input      [7:0] din,      // data inputs: expect registered
  input            c0,       // c0 input
  input            c1,       // c1 input
  input            de,       // de input
  output reg [9:0] dout,     // data outputs
  input            vid_gb    // video preamble encoding select
);

  ////////////////////////////////////////////////////////////
  // Counting number of 1s and 0s for each incoming pixel
  // component. Pipe line the result.
  // Register Data Input so it matches the pipe lined adder
  // output
  ////////////////////////////////////////////////////////////
  reg [3:0] n1d; //number of 1s in din
  reg [7:0] din_q;

  always @ (posedge clkin) begin
    n1d <=#1 din[0] + din[1] + din[2] + din[3] + din[4] + din[5] + din[6] + din[7];

    din_q <=#1 din;
  end

  ///////////////////////////////////////////////////////
  // Stage 1: 8 bit -> 9 bit
  // Refer to DVI 1.0 Specification, page 29, Figure 3-5
  ///////////////////////////////////////////////////////
  wire decision1;

  assign decision1 = (n1d > 4'h4) | ((n1d == 4'h4) & (din_q[0] == 1'b0));
/*
  reg [8:0] q_m;
  always @ (posedge clkin) begin
    q_m[0] <=#1 din_q[0];
    q_m[1] <=#1 (decision1) ? (q_m[0] ^~ din_q[1]) : (q_m[0] ^ din_q[1]);
    q_m[2] <=#1 (decision1) ? (q_m[1] ^~ din_q[2]) : (q_m[1] ^ din_q[2]);
    q_m[3] <=#1 (decision1) ? (q_m[2] ^~ din_q[3]) : (q_m[2] ^ din_q[3]);
    q_m[4] <=#1 (decision1) ? (q_m[3] ^~ din_q[4]) : (q_m[3] ^ din_q[4]);
    q_m[5] <=#1 (decision1) ? (q_m[4] ^~ din_q[5]) : (q_m[4] ^ din_q[5]);
    q_m[6] <=#1 (decision1) ? (q_m[5] ^~ din_q[6]) : (q_m[5] ^ din_q[6]);
    q_m[7] <=#1 (decision1) ? (q_m[6] ^~ din_q[7]) : (q_m[6] ^ din_q[7]);
    q_m[8] <=#1 (decision1) ? 1'b0 : 1'b1;
  end
*/
  wire [8:0] q_m;
  assign q_m[0] = din_q[0];
  assign q_m[1] = (decision1) ? (q_m[0] ^~ din_q[1]) : (q_m[0] ^ din_q[1]);
  assign q_m[2] = (decision1) ? (q_m[1] ^~ din_q[2]) : (q_m[1] ^ din_q[2]);
  assign q_m[3] = (decision1) ? (q_m[2] ^~ din_q[3]) : (q_m[2] ^ din_q[3]);
  assign q_m[4] = (decision1) ? (q_m[3] ^~ din_q[4]) : (q_m[3] ^ din_q[4]);
  assign q_m[5] = (decision1) ? (q_m[4] ^~ din_q[5]) : (q_m[4] ^ din_q[5]);
  assign q_m[6] = (decision1) ? (q_m[5] ^~ din_q[6]) : (q_m[5] ^ din_q[6]);
  assign q_m[7] = (decision1) ? (q_m[6] ^~ din_q[7]) : (q_m[6] ^ din_q[7]);
  assign q_m[8] = (decision1) ? 1'b0 : 1'b1;

  /////////////////////////////////////////////////////////
  // Stage 2: 9 bit -> 10 bit
  // Refer to DVI 1.0 Specification, page 29, Figure 3-5
  /////////////////////////////////////////////////////////
  reg [3:0] n1q_m, n0q_m; // number of 1s and 0s for q_m
  always @ (posedge clkin) begin
    n1q_m  <=#1 q_m[0] + q_m[1] + q_m[2] + q_m[3] + q_m[4] + q_m[5] + q_m[6] + q_m[7];
    n0q_m  <=#1 4'h8 - (q_m[0] + q_m[1] + q_m[2] + q_m[3] + q_m[4] + q_m[5] + q_m[6] + q_m[7]);
  end

  parameter CTRLTOKEN0 = 10'b1101010100;
  parameter CTRLTOKEN1 = 10'b0010101011;
  parameter CTRLTOKEN2 = 10'b0101010100;
  parameter CTRLTOKEN3 = 10'b1010101011;

   parameter CTLBLUGB = 10'b1011001100;
   parameter CTLGRNGB = 10'b0100110011;
   parameter CTLREDGB = 10'b1011001100;

  reg [4:0] cnt; //disparity counter, MSB is the sign bit
  wire decision2, decision3;

  assign decision2 = (cnt == 5'h0) | (n1q_m == n0q_m);
  /////////////////////////////////////////////////////////////////////////
  // [(cnt > 0) and (N1q_m > N0q_m)] or [(cnt < 0) and (N0q_m > N1q_m)]
  /////////////////////////////////////////////////////////////////////////
  assign decision3 = (~cnt[4] & (n1q_m > n0q_m)) | (cnt[4] & (n0q_m > n1q_m));

  ////////////////////////////////////
  // pipe line alignment
  ////////////////////////////////////
  reg       de_q, de_reg;
  reg       c0_q, c1_q;
  reg       c0_reg, c1_reg;
  reg [8:0] q_m_reg;
  reg 	    vid_gb_q, vid_gb_reg;
   

  always @ (posedge clkin) begin
    de_q    <=#1 de;
    de_reg  <=#1 de_q;
    
    c0_q    <=#1 c0;
    c0_reg  <=#1 c0_q;
    c1_q    <=#1 c1;
    c1_reg  <=#1 c1_q;

    q_m_reg <=#1 q_m;

     vid_gb_q <=#1 vid_gb;
     vid_gb_reg <=#1 vid_gb_q;
  end

  ///////////////////////////////
  // 10-bit out
  // disparity counter
  ///////////////////////////////
   always @ (posedge clkin or posedge rstin) begin
      if(rstin) begin
	 dout <= 10'h0;
	 cnt <= 5'h0;
      end else begin
	 if(vid_gb_reg) begin
	     // video preamble coding
	    dout[9:0] <= CTLREDGB;
	 end else begin
	    if (de_reg) begin
               if(decision2) begin
		  dout[9]   <=#1 ~q_m_reg[8]; 
		  dout[8]   <=#1 q_m_reg[8]; 
		  dout[7:0] <=#1 (q_m_reg[8]) ? q_m_reg[7:0] : ~q_m_reg[7:0];
		  
		  cnt <=#1 (~q_m_reg[8]) ? (cnt + n0q_m - n1q_m) : (cnt + n1q_m - n0q_m);
               end else begin
		  if(decision3) begin
		     dout[9]   <=#1 1'b1;
		     dout[8]   <=#1 q_m_reg[8];
		     dout[7:0] <=#1 ~q_m_reg[7:0];
		     
		     cnt <=#1 cnt + {q_m_reg[8], 1'b0} + (n0q_m - n1q_m);
		  end else begin
		     dout[9]   <=#1 1'b0;
		     dout[8]   <=#1 q_m_reg[8];
		     dout[7:0] <=#1 q_m_reg[7:0];
		     
		     cnt <=#1 cnt - {~q_m_reg[8], 1'b0} + (n1q_m - n0q_m);
		  end
               end
	    end else begin
               case ({c1_reg, c0_reg})
		 2'b00:   dout <=#1 CTRLTOKEN0;
		 2'b01:   dout <=#1 CTRLTOKEN1;
		 2'b10:   dout <=#1 CTRLTOKEN2;
		 default: dout <=#1 CTRLTOKEN3;
               endcase
	       
               cnt <=#1 5'h0;
	    end // else: !if(de_reg)
	 end // if (vid_gb)
      end // else: !if(rstin)
   end // always @ (posedge clkin or posedge rstin)
   
   
endmodule