Verilog手绘FVH信号

`timescale 1ns / 1ps
//////////////////////////////////////////////////////////////////////////////////
// Company: 
// Engineer: chensimin
// 
// Create Date: 2018/09/17 13:20:06
// Design Name: 
// Module Name: ntsc_fvh
// Project Name: 
// Target Devices: 
// Tool Versions: 
// Description: 
// 
// Dependencies: 
// 
// Revision:
// Revision 0.01 - File Created
// Additional Comments:
// 
//////////////////////////////////////////////////////////////////////////////////


module ntsc_fvh(

    input wire  clk,       //27MHz
    input wire  rst,
    input wire  enable,

    output wire  hsout,
    output wire  vsout,
    output wire  oeout

    );


parameter THSOUT = 65;     //2.4us
parameter H_TOTAL = 1716;   //64us
parameter V_TOTAL = 525;


wire hsout_falling;

//-------------------------------------------------

reg [15:0]hsout_cnt = 0;
always @(posedge clk or  posedge rst)
begin
    if(rst)
        hsout_cnt <= 0;

    else if(enable)
    begin
        if(hsout_cnt == H_TOTAL)
            hsout_cnt <= 1;
        else 
            hsout_cnt <= hsout_cnt + 1'b1;
    end

    else 
        hsout_cnt <= 0;

end

//-------------------------------------------------

reg hsout_reg = 1'b1 ;
always @(posedge clk or  posedge rst)
begin
    if(rst)
        hsout_reg <= 1'b1;

    else if(enable)
    begin
        if(hsout_cnt <= THSOUT - 1 || hsout_cnt == H_TOTAL)
            hsout_reg <= 1'b0;
        else if(hsout_cnt >= THSOUT && hsout_cnt <= H_TOTAL - 1)
            hsout_reg <= 1'b1;
    end

    else 
        hsout_reg <= 1'b1;
end

//-------------------------------------------------

reg hsout_reg_delay = 1'b1;
always @(posedge clk or  posedge rst)
begin
    if(rst)
        hsout_reg_delay <= 1'b1;

    else if(enable)
         hsout_reg_delay <= hsout_reg;

    else 
        hsout_reg_delay <= 1'b1;

end

//-------------------------------------------------

reg [15:0] hsout_falling_cnt = 0;
always @(posedge clk or  posedge rst)
begin
    if(rst)
        hsout_falling_cnt <= 0;

    else if(enable)
    begin

        if(hsout_falling_cnt == V_TOTAL)
        begin
            hsout_falling_cnt <= V_TOTAL;
            if(hsout_falling)
                hsout_falling_cnt <= 1;
        end

        else if(hsout_falling)
            hsout_falling_cnt <= hsout_falling_cnt + 1'b1;
    end

    else 
        hsout_falling_cnt <= 1'b0;

end

//-------------------------------------------------

reg vsout_reg = 1'b1;
reg oeout_reg = 1'b0;
always @(posedge clk or  posedge rst)
begin
    if(rst)
    begin
        vsout_reg <= 1'b1;
        oeout_reg <= 1'b0;
    end

    else if(enable)
    begin

        if(hsout_falling_cnt < 4 || (hsout_falling_cnt == 4 && hsout_cnt < 871 && hsout_cnt >1))
        begin
            vsout_reg <= 1'b1;
            oeout_reg <= 1'b0;
        end

        else if(hsout_falling_cnt == 4 && hsout_cnt == 871)
        begin
            vsout_reg <= 1'b0;
            oeout_reg <= 1'b1;
        end

        else if(hsout_falling_cnt == 7 && hsout_cnt == 871)
            vsout_reg <= 1'b1;

        else if(hsout_falling_cnt == 267 && hsout_cnt == 13)
        begin
            vsout_reg <= 1'b0;
            oeout_reg <= 1'b0;
        end

        else if(hsout_falling_cnt == 270 && hsout_cnt == 13)
            vsout_reg <= 1'b1;

        else 
        begin
            vsout_reg <= vsout_reg;
            oeout_reg <= oeout_reg;
        end
    end
end

//-------------------------------------------------

assign hsout_falling = hsout_reg_delay && (!hsout_reg);
assign hsout = hsout_reg;
assign vsout = vsout_reg;
assign oeout = oeout_reg;


endmodule


/*

add_force {/ntsc_fvh/clk} -radix hex {1 0ns} {0 25000ps} -repeat_every 50000ps
add_force {/ntsc_fvh/rst} -radix hex {1 0ns} {0 100ns}
add_force {/ntsc_fvh/enable} -radix hex {1 0ns}

*/