Controlling a Pinball Machine Using Linux

Not everything in the pinball machine control system has to execute as frequently as the low-level hardware I/O operations. Game play itself—how the machine responds to switch detections, lighting different lamps and incrementing the player scores—operates just fine as an ordinary user process. In a sense, it is really a supervisory controller of the low-level I/O processing.

The kernel module should work for every game based on the AS2518 MPU. You can download the source code from the Pinball Machine Reverse-Engineering Kit Project on SourceForge.net and compile it for your kernel. It will then be up to you to write the supervisory control software to play the particular game you are hacking. Table 1 lists other source code files in this package.

You are free to modify the C program testbed.c I wrote for Evel Knievel. It uses the ncurses screen handling package to provide a console color display and user input. A diagnostic display shows the disposition of the switch matrix, the lamps and the most recently fired solenoid. It also shows the player scores, as well as run-time statistics such as the average cycle frequency and execution time of the kernel workqueue process. Keyboard commands can be entered to turn the continuous solenoid on or off, fire momentary solenoids, turn feature lamps on or off and adjust the workqueue delay. Figure 6 shows a game in progress. Note the closed switches; these are drop targets that have been struck.

Figure 6. Supervisory Program Diagnostic Display

The supervisory program receives events passed from the kernel module by reading /dev/pmrek, which it has opened using the system call open(), just like any other file. Commands are then sent back to the module by writing to it. I tried to make the main functions correspond to my impression of the key events in a game of pinball. They are listed in Table 2.

You should be able to adapt this code to your particular game by tweaking the functions game_switch_response() and game_lamp_update(). How do you write the program without peeking at the original manufacturer's source code? There are plenty of clues painted on the play field itself, telling you what each switch scores and so on. Of course, you also can create your own rules, perhaps improving on weaknesses in the original design.

The diagnostic display is great for testing, but the player scores are too small. By default, the console simulates the large digital displays on the original back box, as shown in Figure 7. You can get to the diagnostic display by pressing the Self Test switch inside the pinball machine coin door.

Figure 7. Back Board Score Display

We took the game to Pinball at the Zoo in Kalamazoo, Michigan in April 2005. Hundreds of people played the game, which collected statistical data that I used in my Master's thesis. After each game completes, a PHP program reads through the log file created by the game program. It generates an HTML document summarizing the event history of the game and statistics about its real-time performance. These results are then stored in a MySQL database to facilitate analysis of overall performance. Figure 8 is a block diagram of the setup. Figure 9 shows the game in action.

Figure 8. Computer System Block Diagram

Figure 9. Game in Action at Pinball at the Zoo