Pong on VGA/FPGA
Hannah Tandang, Jiaxing Wang, Jianzheng Ruan, Joseph Sorkin
https://www.youtube.com/watch?v=c240JOul-l0
We will be recreating Pong using Verilog programming to the VGA as our Fall 2024 EC311 final project. It is a two player pong game where players can control the paddles motion by using the switches on an FPGA board to deflect the ball off. Any missed collision with the paddle is a score for the opposing player. The score is displayed on a 7 segment display on the FPGA. The game also contains two buttons "reset" and "start".
- Download the source code as a .zip file and unzip the compressed folder.
- In 0-all-project-files, open ec311project.xpr using Vivado 2024.1 or later.
The following describes the code structure of several relevant main modules:
- vga_top.v: This is the top module of our program. It describes on a high level how each module interacts with eachother via wires and various clock signals, manages the overall state of the game (such as allowing it to start and end). In addition, it contains the highest level VGA code, signaling how each pixel should be displayed. It's also vital to describing how each module conenects to the peripherals (buttons, 7 Segment display), as those are defined as inputs and outputs to this module.
- vga_controller.v: This module manages most of the VGA signal. It scans across the VGA window size, followed by a region of hsync and vsync to abide by the VGA protocol. As it draws, it interacts with the rectangle.v module to decide whether or not a game object is contained in the current pixel being drawn. It runs off of a 25MHz clock divided in vga_top.v
- ball.v: The ball module is responsible for updating and declaring the ball's position at a given state with the corresponding velocity. The module sets the initial ball position at the center of the canvas, and once the "start" button is pressed on the FPGA board, it checks the condition with the clock signal to update the ball's position using 2's complement addition. While the ball's position is being captured and updated every second, we have loops nested with if statements to check for collisions. There are three collisions we took into consideration. One is the top and bottom of the screen, which will cause the ball to just bounce off, then we check collision with the paddles if the paddle collision is detected, then we inverse the velocity and add to the ball position at that instance, lastly, we check for ball collision with the right and left edges, if those collisions are detected, an internal reset flag is being triggered, causing only the ball's position to reset to the beginning, and the opposing player score will go up by one. There is also a reset button that clears out the whole game memory and sets it to the very beginning state, with ball and player scores to be zero. Velocity also varies depending on the section of the paddle collision is being detected. Finally, it outputs the ball position to other modules and feeds into the VGA top.
- ball_collision.v: Whenever the ball collides with a paddle, it will change velocity. Currently, the x-velocity is reversed and then sped up by one unit (to make the game more intense), and the y-velocity changes depending on where the ball hit the paddle. When a reset flag is triggered, the ball speed resets to 2, and its default direction changes whenever the player with the lowest score changes.
- score.v: This module communicates with the top module, registers within ball.v, and keeps track of the score for each left and right player and displays it on the FPGA 7 segment display. Within ball.v, top score is limited to 4. As Lscore and Rscore and integers of the number of times the ball collides with the opposing wall (does not hit the paddle), and is also an input to other modules. It then takes these inputs and turns it ino a number in the thousands. This number is then divided by tens to display each integer as the different anodes are activate and deactivated really fast. The integers are then converted into the corresponding 7 segment 7 bit numbers as defined in the case statement at the bottom. In the end, the score is displayed on the left most 4 numbers as: (Left score)00(Right score).
- rectangle.v: This module generates rectangles to be drawn by vga_controller.v. It takes in the current pixel being drawn, as well as the position and dimensions of the rectangle. It outputs whether or not the current pixel being drawn is contained in the rectangle, allowing the screen to display it at its relevant position.
- paddle.v: This paddle module is instantiated twice to create two different paddle objects. Each paddle will be initialized to have a velocity of 2 and an initial y-position of 240 (middle height). Whenever the switch input is up, the paddle position increases by the given velocity (2). When the switch input is down, the paddle decreases by the given velocity.
- game_clk_divider.v: Game clock divider slows down the speed of the game, allowing it to run at around 13MHz, providing more precision with integer velocities.
- clk_divider.v: Clock divider slows down the internal 100MHz clock to 25MHz to provide the VGA with a more proper clock speed