module vga_ctrl(
    input  wire             clk_25      ,
    input  wire             vga_rst_n   ,
    input  wire  [15: 0]    rgb_data    ,
    output wire             hsync       ,
    output wire             vsync       ,
    output wire  [9: 0]     pixel_x     ,
    output wire  [9: 0]     pixel_y     ,
    output wire  [15: 0]    vga_data    
);
//行
parameter  H_SYNC  = 10'd96  ,
           H_BACK  = 10'd40  ,
           H_LEFT  = 10'd8   ,
           H_AREA  = 10'd640 ,
           H_RIGHT = 10'd8   ,
           H_FRONT = 10'd8   ,
           H_TOTAL = 10'd800 ;
//列
parameter  V_SYNC   = 10'd2  ,
           V_BACK   = 10'd25 ,
           V_TOP    = 10'd8  ,
           V_AREA   = 10'd480,
           V_BUTTON = 10'd8  ,
           V_FRONT  = 10'd2  ,
           V_TOTAL  = 10'd525;
//像素计数
reg [9: 0] cnt_pixel;
wire       add_cnt_pixel;
wire       end_cnt_pixel;
//行计数
reg [9: 0] cnt_row;
wire       add_cnt_row;
wire       end_cnt_row;

wire       area_vld;
wire       vld_req ;
always @(posedge clk_25 or negedge vga_rst_n) begin
    if(!vga_rst_n)begin
        cnt_pixel <= 10'd0;
    end 
    else if(add_cnt_pixel)begin
        if(end_cnt_pixel)begin
            cnt_pixel <= 10'd0;
        end 
        else begin
            cnt_pixel <= cnt_pixel + 1'd1;
        end 
    end 
    else begin
        cnt_pixel <= cnt_pixel;
    end 
end
assign add_cnt_pixel = 1'b1;
assign end_cnt_pixel = add_cnt_pixel && cnt_pixel == (H_TOTAL - 1'd1);

always @(posedge clk_25 or negedge vga_rst_n)begin
    if(!vga_rst_n)begin
        cnt_row <= 10'd0;
    end 
    else if(add_cnt_row)begin
        if(end_cnt_row)begin
            cnt_row <= 10'd0;
        end 
        else begin
            cnt_row <= cnt_row + 1'd1;
        end 
    end 
    else begin
        cnt_row <= cnt_row;
    end 
end   
assign add_cnt_row = end_cnt_pixel;
assign end_cnt_row = add_cnt_row && cnt_row == V_TOTAL - 1'd1;  
assign hsync = (cnt_pixel <= H_SYNC - 1'd1) ? 1'b1: 1'b0; 
assign vsync = (cnt_row <= V_SYNC - 1'd1) ? 1'b1: 1'b0;
assign area_vld = (cnt_pixel >= (H_SYNC + H_BACK + H_LEFT)) && 
                  (cnt_pixel < (H_SYNC + H_BACK + H_LEFT + H_AREA)) &&
                  (cnt_row >= (V_SYNC + V_BACK + V_TOP)) &&
                  (cnt_row < (V_SYNC + V_BACK + V_TOP + V_AREA));
assign vld_req = (cnt_pixel >= (H_SYNC + H_BACK + H_LEFT - 1'd1)) && 
                 (cnt_pixel < (H_SYNC + H_BACK + H_LEFT + H_AREA - 1'd1)) &&
                 (cnt_row >= (V_SYNC + V_BACK + V_TOP)) &&
                 (cnt_row < (V_SYNC + V_BACK + V_TOP + V_AREA));
//超前一个时钟周期，目的是为了时序对齐
assign pixel_x = (vld_req == 1'b1) ? (cnt_pixel - (H_SYNC + H_BACK + H_LEFT - 1'b1)): 10'h3ff;
assign pixel_y = (vld_req == 1'b1) ? (cnt_row - (V_SYNC + V_BACK + V_TOP)): 10'h3ff;
assign vga_data = (area_vld == 1'b1) ? rgb_data: 16'h0000;
endmodule