Pong Game on an FPGA with VGA Video and a Custom Board

Overview

This project is a Pong game I built on an FPGA in 2016. There is no processor or software: the whole game, from VGA video generation to the movement of the ball, runs as digital hardware described in VHDL on a Spartan-6. I also designed the FPGA board in Altium Designer, and the picture appears on an LCD display. The game screen shows the name and address of this website.

How the game works

The game has three screens, and a state machine moves between them:

• Start screen: waits for the Start button, with a flashing message.

• Play screen: a green ball moves around the screen and bounces off the top wall and the side walls. The player moves a red paddle at the bottom with the left and right buttons to send the ball back.

• Game-over screen: if the ball gets past the paddle the game ends, and the Start button begins it again.

The Reset button returns the game to the start screen at any time. The diagram below shows the parts inside the FPGA and the signal path.

VGA video generation

The picture is generated at 640×480 and 60 Hz. The 50 MHz board clock is divided to 25 MHz to make the pixel clock, and two counters, one for pixels and one for lines, produce the sync signals (H-Sync and V-Sync) and give every game part the coordinates of the current pixel. Each part compares those coordinates with its own shape and decides what color the pixel should be, so no frame memory is needed and everything is drawn on the fly. A 3-bit RGB output and the two sync signals go to the display.

Ball and paddle movement

The game updates once per frame, about every 16 ms. The paddle moves 6 pixels per frame and the ball 3 pixels in each direction. When the ball hits the top wall or the side walls, or the paddle, its direction reverses. If the ball falls below the paddle's height, the game goes to the game-over state.

Specifications

• FPGA: Xilinx Spartan-6, model XC6SLX9

• Code: VHDL, with the Xilinx ISE tools

• VGA output at 640×480 and 60 Hz, 3-bit color

• Inputs: four buttons (left, right, Start, Reset)

• Three screens: start, play, game over

• Main clock: 50 MHz

• Powered over USB

Hardware design

I designed the board under the FPGA myself. It has these parts:

• The XC6SLX9 FPGA in a TQG144 package and a 50 MHz oscillator

• An SPI flash memory that holds the configuration, so the FPGA starts by itself after every power-up

• An FT2232HL chip for the USB connection: FPGA programming over JTAG and a parallel data channel

• Two AMS1117 regulators, one for 3.3 V and one for 1.2 V, powered from the 5 V of USB

• Five switches: Reset, left, right, Start and a configuration switch

• LEDs for power and for the end of FPGA configuration

• An output header for VGA and a power terminal

The pictures below show the game running, the 3D view and the PCB layout, and the schematic.

Result

A complete game with live video that runs as digital hardware without any processor, together with the board that was designed and built for it.