VGA_Sync_Porch.v

// The purpose of this module is to modify the input HSync and VSync signals to
// include some time for what is called the Front and Back porch.  The front
// and back porch of a VGA interface used to have more meaning when a monitor
// actually used a Cathode Ray Tube (CRT) to draw an image on the screen.  You
// can read more about the details of how old VGA monitors worked.  These
// days, the notion of a front and back porch is maintained, due more to
// convention than to the physics of the monitor.
// New standards like DVI and HDMI which are meant for digital signals have
// removed this notion of the front and back porches.  Remember that VGA is an
// analog interface.
// This module is designed for 640x480 with a 25 MHz input clock.

module VGA_Sync_Porch #(parameter VIDEO_WIDTH = 3,  // remember to 
                        parameter TOTAL_COLS  = 3,  // overwrite
                        parameter TOTAL_ROWS  = 3,  // these defaults
                        parameter ACTIVE_COLS = 2,
                        parameter ACTIVE_ROWS = 2)
  (input i_Clk,
   input i_HSync,
   input i_VSync,
   input [VIDEO_WIDTH-1:0] i_Red_Video,
   input [VIDEO_WIDTH-1:0] i_Grn_Video,
   input [VIDEO_WIDTH-1:0] i_Blu_Video,
   output reg o_HSync,
   output reg o_VSync,
   output reg [VIDEO_WIDTH-1:0] o_Red_Video,
   output reg [VIDEO_WIDTH-1:0] o_Grn_Video,
   output reg [VIDEO_WIDTH-1:0] o_Blu_Video
   );

  parameter c_FRONT_PORCH_HORZ = 18;
  parameter c_BACK_PORCH_HORZ  = 50;
  parameter c_FRONT_PORCH_VERT = 10;
  parameter c_BACK_PORCH_VERT  = 33;

  wire w_HSync;
  wire w_VSync;
  
  wire [9:0] w_Col_Count;
  wire [9:0] w_Row_Count;
  
  reg [VIDEO_WIDTH-1:0] r_Red_Video = 0;
  reg [VIDEO_WIDTH-1:0] r_Grn_Video = 0;
  reg [VIDEO_WIDTH-1:0] r_Blu_Video = 0;
  
  Sync_To_Count #(.TOTAL_COLS(TOTAL_COLS),
                  .TOTAL_ROWS(TOTAL_ROWS)) UUT 
  (.i_Clk      (i_Clk),
   .i_HSync    (i_HSync),
   .i_VSync    (i_VSync),
   .o_HSync    (w_HSync),
   .o_VSync    (w_VSync),
   .o_Col_Count(w_Col_Count),
   .o_Row_Count(w_Row_Count)
  );
	  
  // Purpose: Modifies the HSync and VSync signals to include Front/Back Porch
  always @(posedge i_Clk)
  begin
    if ((w_Col_Count < c_FRONT_PORCH_HORZ + ACTIVE_COLS) || 
        (w_Col_Count > TOTAL_COLS - c_BACK_PORCH_HORZ - 1))
      o_HSync <= 1'b1;
    else
      o_HSync <= w_HSync;
    
    if ((w_Row_Count < c_FRONT_PORCH_VERT + ACTIVE_ROWS) ||
        (w_Row_Count > TOTAL_ROWS - c_BACK_PORCH_VERT - 1))
      o_VSync <= 1'b1;
    else
      o_VSync <= w_VSync;
  end

  
  // Purpose: Align input video to modified Sync pulses.
  // Adds in 2 Clock Cycles of Delay
  always @(posedge i_Clk)
  begin
    r_Red_Video <= i_Red_Video;
    r_Grn_Video <= i_Grn_Video;
    r_Blu_Video <= i_Blu_Video;

    o_Red_Video <= r_Red_Video;
    o_Grn_Video <= r_Grn_Video;
    o_Blu_Video <= r_Blu_Video;
  end
  
endmodule