Pong on the Mojo Revisited

Pong on the Mojo Revisited

In my previous post, I briefly discussed the implementation of a pseudo-pong game on my Mojo FPGA developer board.

I was able to implement the VHDL version that I linked to later in the post and it works much better.

The biggest challenge I had with it was converting the two-button input to a potentiometer input. It turns out all I had to do was convert an array to an integer as input to the paddle's left position.

Here is a link to the article describing the implementation that I used:

FPGA Pong From FPGACenter.com.

The VHDL was a big challenge for me because I had to learn it as I went along. It works just like Verilog, but the syntax is so different.

Also, I modified my User Constraints File to make the RGB an array for compatibility with this particular implementation.

Here are the new custom constraints:

NET "rgb<2>" LOC = P41 | IOSTANDARD = LVTTL;
NET "rgb<1>" LOC = P40 | IOSTANDARD = LVTTL;
NET "rgb<0>" LOC = P35 | IOSTANDARD = LVTTL;

Here is the code containing my changes (in the vga_control and img_gen modules):


library IEEE;

entity vga_control is
     Port ( clk : in STD_LOGIC;
                start : in STD_LOGIC;
                reset : in STD_LOGIC;
                paddle : IN STD_LOGIC_VECTOR(9 downto 0);
                rgb : out STD_LOGIC_VECTOR (2 downto 0);
                h_s : out STD_LOGIC;
                v_s : out STD_LOGIC);
end vga_control;

architecture Behavioral of vga_control is

       PORT( clk : IN std_logic;
                     x_control : IN std_logic_vector(9 downto 0);
                     paddle : IN std_logic_vector(9 downto 0);
                     y_control : IN std_logic_vector(9 downto 0);
                     video_on : IN std_logic; 
                     rgb : OUT std_logic_vector(2 downto 0) );

COMPONENT sync_mod
       PORT( clk : IN std_logic;
                     reset : IN std_logic;
                     start : IN std_logic; 
                     y_control : OUT std_logic_vector(9 downto 0);
                     x_control : OUT std_logic_vector(9 downto 0);
                     h_s : OUT std_logic;
                     v_s : OUT std_logic;
                     video_on : OUT std_logic );

signal x,y:std_logic_vector(9 downto 0);
signal video:std_logic;

          U1: img_gen PORT MAP( clk =>clk , x_control => x, paddle => paddle , 
                                                         y_control => y, video_on =>video , rgb => rgb );

           U2: sync_mod PORT MAP( clk => clk, reset => reset, start => start, y_control => y, x_control =>x ,
                                                             h_s => h_s , v_s => v_s, video_on =>video );
end Behavioral;

My changes are on lines 9, 20, and 41. This sends the output from the potentiometer hooked up to the ADC on the Mojo to the img_gen module where it's converted to position data for the paddle control.

Here's the modified img_gen code:

library IEEE;

entity img_gen is
     Port ( clk : in STD_LOGIC;
                x_control : in STD_LOGIC_VECTOR(9 downto 0);
                paddle : in STD_LOGIC_VECTOR(9 downto 0);
                y_control : in STD_LOGIC_VECTOR(9 downto 0);
                video_on : in STD_LOGIC;
                rgb : out STD_LOGIC_VECTOR(2 downto 0));
end img_gen;

architecture Behavioral of img_gen is

constant wall_l:integer :=10;--the distance between wall and left side of screen
constant wall_t:integer :=10;--the distance between wall and top side of screen
constant wall_k:integer :=10;--wall thickness
signal wall_on:std_logic; 
signal rgb_wall:std_logic_vector(2 downto 0); 

signal bar_l, bar_l_next: integer:=100;
constant bar_t:integer :=420;--the distance between bar and top side of screen
constant bar_k:integer :=10;--bar thickness
constant bar_w:integer:=120;--bar width
constant bar_v:integer:=10;--velocity of the bar
signal bar_on:std_logic;
signal rgb_bar:std_logic_vector(2 downto 0); 

signal ball_l,ball_l_next:integer :=100;--the distance between ball and left side of screen
signal ball_t,ball_t_next:integer :=100; --the distance between ball and top side of screen
constant ball_w:integer :=20;--ball Height
constant ball_u:integer :=20;--ball width
constant x_v,y_v:integer:=3;-- horizontal and vertical speeds of the ball 
signal ball_on:std_logic;
signal rgb_ball:std_logic_vector(2 downto 0); 

signal refresh_reg,refresh_next:integer;
constant refresh_constant:integer:=830000;
signal refresh_tick:std_logic;

--ball animation
signal xv_reg,xv_next:integer:=3;--variable of the horizontal speed
signal yv_reg,yv_next:integer:=3;--variable of the vertical speed

--x,y pixel cursor
signal x,y:integer range 0 to 650;

signal vdbt:std_logic_vector(3 downto 0);

signal rgb_reg,rgb_next:std_logic_vector(2 downto 0);


--x,y pixel cursor
x <= conv_integer(x_control); y <="conv_integer(y_control" ); --refreshing process(clk) begin if clk'event and clk="1" then refresh_reg<="refresh_next;" end if; process; refresh_next when refresh_reg="refresh_constant" else refresh_reg+1; refresh_tick '0'; --register part ball_l ball_t xv_reg yv_reg bar_l --bar animation process(refresh_tick,paddle) bar_l_next --ball process(refresh_tick,ball_l,ball_t,xv_reg,yv_reg) ball_l_next ball_t_next xv_next yv_next> 400 and ball_l > (bar_l -ball_u) and ball_l < (bar_l +120) then --the ball hits the bar
           yv_next <= 10 35 -y_v ; elsif ball_t < then--the ball hits the wall yv_next end if; if ball_l then --the left side of screen xv_next> 600 then 
          xv_next <= -x_v ; --the ball hits the right side of screen end if; ball_l_next <="ball_l" + xv_reg; ball_t_next yv_reg; process; --wall object wall_on when x> wall_l and x < (640-wall_l) and y> wall_t and y < (wall_t+ wall_k) else
rgb_wall <= "000";--black --bar object bar_on <="1" when x> bar_l and x < (bar_l+bar_w) and y> bar_t and y < (bar_t+ bar_k) else
rgb_bar <= "001";--blue --ball object ball_on <="1" when x> ball_l and x < (ball_l+ball_u) and y> ball_t and y < (ball_t+ ball_w) else
rgb_ball <= "010"; --green --buffer process(clk) begin if clk'event and clk="1" then rgb_reg <="rgb_next;" end if; process; --mux vdbt<="video_on" & wall_on bar_on &ball_on; with vdbt select rgb_next when "1000",--background of the screen is red rgb_wall "1100", "1101", rgb_bar "1010", "1011", rgb_ball "1001", "000" others; --output rgb behavioral;< code>

My changes are on lines 10 and 95 to make the potentiometer control the paddle.