VHDL Ping Pong Game on Cyclone IV EP4CE22 - Display Not Updating Correctly

Question

I'm trying to implement a Ping Pong game using VHDL on a Cyclone IV FPGA (EP4CE22) with ModelSim as my simulation tool. I have the basic game logic implemented, but I'm facing an issue with the display not updating correctly.

*Here's my VHDL code:

library IEEE;
use IEEE.STD_LOGIC_1164.ALL;
use IEEE.STD_LOGIC_ARITH.ALL;
use IEEE.STD_LOGIC_UNSIGNED.ALL;

-- entity start
entity PingPongGame is
    Port ( clk : in STD_LOGIC;
           reset : in STD_LOGIC;
           vga_hsync : out STD_LOGIC;
           vga_vsync : out STD_LOGIC;
           vga_red, vga_green, vga_blue : out STD_LOGIC_VECTOR(7 downto 0);
           paddle_up, paddle_down : in STD_LOGIC);
end PingPongGame;
-- entity end

--architecture start
architecture Behavioral of PingPongGame is
    signal h_counter : integer range 0 to 799 := 0;
    signal v_counter : integer range 0 to 524 := 0;
    signal row, col : integer range 0 to 639 := 0;
    signal ball_x, ball_y, paddle_y : integer range 0 to 479 := 0;
    signal ball_x_velocity, ball_y_velocity : integer := 1;
    signal ball_color, paddle_color, background_color : STD_LOGIC_VECTOR(7 downto 0);
    signal ball_visible, paddle_visible : STD_LOGIC := '0';
    
begin
    -- VGA timing process
    VGA_TIMING: process (clk, reset)
    begin
        if reset = '1' then
            h_counter <= 0;
            v_counter <= 0;
            row <= 0;
            col <= 0;
        elsif rising_edge(clk) then
            if h_counter < 799 then
                h_counter <= h_counter + 1;
            else
                h_counter <= 0;
                if v_counter < 524 then
                    v_counter <= v_counter + 1;
                else
                    v_counter <= 0;
                end if;
            end if;
        end if;
    end process;

    -- Synchronize VGA signals
    vga_hsync <= '1' when (h_counter < 96) else '0';
    vga_vsync <= '1' when (v_counter < 2) else '0';

    -- Calculate row and col positions
    row <= v_counter - 2;
    col <= h_counter - 96;

    -- Ball, paddle, and background colors
    ball_color <= "11110000"; -- Example color for the ball (adjust as needed)
    paddle_color <= "00001111"; -- Example color for the paddle (adjust as needed)
    background_color <= "00000000"; -- Example background color (adjust as needed)

    -- Game logic for ball movement and collision detection
    process (clk)
    begin
        if rising_edge(clk) then
            if row = ball_y and col = ball_x then
                ball_visible <= '1';
            else
                ball_visible <= '0';
            end if;
            
            if row >= paddle_y and row < paddle_y + 32 and col = 10 then
                paddle_visible <= '1';
            else
                paddle_visible <= '0';
            end if;
            
            if ball_visible = '1' then
                ball_x <= ball_x + ball_x_velocity;
                ball_y <= ball_y + ball_y_velocity;

                -- Collision detection with top and bottom boundaries
                if ball_y <= 0 or ball_y >= 472 then
                    ball_y_velocity <= -ball_y_velocity; -- Reverse vertical velocity
                end if;

                -- Collision detection with paddle
                if col = 10 and paddle_visible = '1' then
                    ball_x_velocity <= -ball_x_velocity; -- Reverse horizontal velocity
                end if;

                -- Scoring logic (ball goes out of bounds)
                if ball_x <= 0 or ball_x >= 632 then
                    ball_x <= 320;
                    ball_y <= 240;
                    ball_x_velocity <= 1; -- Reset velocity
                    ball_y_velocity <= 1; -- Reset velocity
                end if;
            end if;

            -- Paddle control
            if paddle_up = '1' and paddle_y > 0 then
                paddle_y <= paddle_y - 1;
            elsif paddle_down = '1' and paddle_y < 448 then
                paddle_y <= paddle_y + 1;
            end if;
        end if;
    end process;

    -- Output VGA colors based on game logic
    process (ball_visible, paddle_visible)
    begin
        if ball_visible = '1' then
            vga_red <= ball_color;
            vga_green <= ball_color;
            vga_blue <= ball_color;
        elsif paddle_visible = '1' then
            vga_red <= paddle_color;
            vga_green <= paddle_color;
            vga_blue <= paddle_color;
        else
            vga_red <= background_color;
            vga_green <= background_color;
            vga_blue <= background_color;
        end if;
    end process;
    
end Behavioral;
--architecture end

The problem I'm facing is that the ball and paddle are not updating their positions correctly on the display. They appear to be stuck or flickering. I suspect there might be an issue with the timing or the way I'm updating the display.

What I've Tried:

1. Checked the VGA timing signals, and they seem to be correct.
2. Verified the game logic for ball and paddle movement, and it appears to be working as expected.
3. Made sure that the VGA controller is correctly configured for the Cyclone IV FPGA.

Update: Issue Resolved

The issue with the display not updating correctly in my Ping Pong game on the Cyclone IV FPGA (EP4CE22) with ModelSim has been successfully resolved. After thorough investigation and troubleshooting, I discovered that the problem was related to the FPGA configuration and ModelSim simulation rather than the VHDL code itself.

Answer 1

Issue Resolved

The issue with the display not updating correctly in my Ping Pong game on the Cyclone IV FPGA (EP4CE22) with ModelSim has been successfully resolved. After thorough investigation and troubleshooting, I discovered that the problem was related to the FPGA configuration and ModelSim simulation rather than the VHDL code itself.