# vga driver code

module vga_driver
(
    input                   I_clk   , 
    input                   I_rst_n , 
    output   reg   [7:0]    O_red   ,
    output   reg   [7:0]    O_green , 
    output   reg   [7:0]    O_blue  , 
    output                  O_hs    , 
    output                  O_vs    , 
    output reg O_clk_25M,
    output reg O_blank_n,
    output reg O_sync_n
);

// 分辨率为640*480时行时序各个参数定义
parameter       C_H_SYNC_PULSE      =   96  , 
                C_H_BACK_PORCH      =   48  ,
                C_H_ACTIVE_TIME     =   640 ,
                C_H_FRONT_PORCH     =   16  ,
                C_H_LINE_PERIOD     =   800 ;

// 分辨率为640*480时场时序各个参数定义               
parameter       C_V_SYNC_PULSE      =   2   , 
                C_V_BACK_PORCH      =   33  ,
                C_V_ACTIVE_TIME     =   480 ,
                C_V_FRONT_PORCH     =   10  ,
                C_V_FRAME_PERIOD    =   525 ;
                
parameter       C_COLOR_BAR_WIDTH   =   C_H_ACTIVE_TIME / 8  ;  

reg [11:0]      R_h_cnt         ; 
reg [11:0]      R_v_cnt         ; 
reg             R_clk_25M       ;

wire            W_active_flag   ; 


always @(posedge I_clk or negedge I_rst_n)
begin
    if(!I_rst_n)
        R_clk_25M   <=  1'b0        ;
    else
        R_clk_25M   <=  ~R_clk_25M  ;     
end

//設定O_clk_25M  O_blank_n  O_sync_n
always@(*)begin
    O_clk_25M=R_clk_25M;
    O_blank_n=1'd1;
    O_sync_n=1'd0;
end
//
always @(posedge R_clk_25M or negedge I_rst_n)
begin
    if(!I_rst_n)
        R_h_cnt <=  12'd0   ;
    else if(R_h_cnt == C_H_LINE_PERIOD - 1'b1)
        R_h_cnt <=  12'd0   ;
    else
        R_h_cnt <=  R_h_cnt + 1'b1  ;                
end                

assign O_hs =   (R_h_cnt < C_H_SYNC_PULSE) ? 1'b0 : 1'b1    ; 


always @(posedge R_clk_25M or negedge I_rst_n)
begin
    if(!I_rst_n)
        R_v_cnt <=  12'd0   ;
    else if(R_v_cnt == C_V_FRAME_PERIOD - 1'b1)
        R_v_cnt <=  12'd0   ;
    else if(R_h_cnt == C_H_LINE_PERIOD - 1'b1)
        R_v_cnt <=  R_v_cnt + 1'b1  ;
    else
        R_v_cnt <=  R_v_cnt ;                        
end                

assign O_vs =   (R_v_cnt < C_V_SYNC_PULSE) ? 1'b0 : 1'b1    ; 
//////////////////////////////////////////////////////////////////  

assign W_active_flag =  (R_h_cnt >= (C_H_SYNC_PULSE + C_H_BACK_PORCH                  ))  &&
                        (R_h_cnt <= (C_H_SYNC_PULSE + C_H_BACK_PORCH + C_H_ACTIVE_TIME))  && 
                        (R_v_cnt >= (C_V_SYNC_PULSE + C_V_BACK_PORCH                  ))  &&
                        (R_v_cnt <= (C_V_SYNC_PULSE + C_V_BACK_PORCH + C_V_ACTIVE_TIME))  ;                     


always @(posedge R_clk_25M or negedge I_rst_n)
begin
    if(!I_rst_n) 
        begin
            O_red   <=  8'b0000_0000    ;
            O_green <=  8'b0000_0000   ;
            O_blue  <=  8'b0000_0000    ; 
        end
    else if(W_active_flag)     
        begin
            if(R_h_cnt < (C_H_SYNC_PULSE + C_H_BACK_PORCH + C_COLOR_BAR_WIDTH))
                begin
                    O_red   <=  8'b1111_1111    ; 
                    O_green <=  8'b0000_0000   ;
                    O_blue  <=  8'b0000_0000    ;
                end
            else if(R_h_cnt < (C_H_SYNC_PULSE + C_H_BACK_PORCH + C_COLOR_BAR_WIDTH*2))
                begin
                    O_red   <=  8'b0000_0000    ;
                    O_green <=  8'b1111_1111   ; 
                    O_blue  <=  8'b0000_0000    ;
                end 
            else if(R_h_cnt < (C_H_SYNC_PULSE + C_H_BACK_PORCH + C_COLOR_BAR_WIDTH*3)) 
                begin
                    O_red   <=  8'b0000_0000    ;
                    O_green <=  8'b0000_0000   ;
                    O_blue  <=  8'b1111_1111    ;
                end 
            else if(R_h_cnt < (C_H_SYNC_PULSE + C_H_BACK_PORCH + C_COLOR_BAR_WIDTH*4)) 
                begin
                    O_red   <=  8'b1111_1111    ; 
                    O_green <=  8'b1111_1111   ; 
                    O_blue  <=  8'b1111_1111    ;
                end 
            else if(R_h_cnt < (C_H_SYNC_PULSE + C_H_BACK_PORCH + C_COLOR_BAR_WIDTH*5)) 
                begin
                    O_red   <=  8'b0000_0000    ; 
                    O_green <=  8'b0000_0000   ;
                    O_blue  <=  8'b0000_0000    ;
                end 
            else if(R_h_cnt < (C_H_SYNC_PULSE + C_H_BACK_PORCH + C_COLOR_BAR_WIDTH*6)) 
                begin
                    O_red   <=  8'b1111_1111    ; 
                    O_green <=  8'b1111_1111   ;
                    O_blue  <=  8'b0000_0000    ; 
                end 
            else if(R_h_cnt < (C_H_SYNC_PULSE + C_H_BACK_PORCH + C_COLOR_BAR_WIDTH*7)) 
                begin
                    O_red   <=  8'b1111_1111    ; 
                    O_green <=  8'b0000_0000   ; 
                    O_blue  <=  8'b1111_1111    ; 
                end 
            else                             
                begin
                    O_red   <=  8'b0000_0000    ; 
                    O_green <=  8'b1111_1111   ; 
                    O_blue  <=  8'b1111_1111    ; 
                end                   
        end
    else
        begin
            O_red   <=  8'b0000_0000    ;
            O_green <=  8'b0000_0000   ;
            O_blue  <=  8'b0000_0000    ; 
        end           
end

endmodule