Silicon8 for Thumby

Silicon8 for Thumby is an interpreter for the CHIP-8, SCHIP and XO-CHIP programming languages. It allows you to run games made for those platforms on your Thumby.

CHIP-8 is an interpreted programming language, going back to the '70s. It was initially used on the COSMAC VIP and Telmac 1800 8-bit microcomputers and was made to allow video games to be more easily programmed for and shared among these computers. In 1990 CHIP-8 saw a revival in the form or SCHIP on HP-48 graphing calculators, and in more recent years the XO-CHIP extension has given it more colours, memory and better sound. Many people still write new software for this platform, not in the least at the yearly Octojam.

As such, there is an impressive library of programs and games available for CHIP-8 and friends. And we can now run almost all of them on Thumby too! 👾🕹

Note: Runs faster and with less flicker on hardware

Due to the limited computing power and low screen resolution of CHIP-8, I thought this is a great fit for the Thumby, and also a testament of how far computers have come. What was once the pinnacle of computer gaming for hobbyists now runs easily on a cheap keychain, with pixels and memory to spare 😄

(The original Silicon8 is written in Go, and targeted mainly at WebAssembly. It can be run in your web browser here. This version of it is a port to MicroPython for the Thumby playable keychain.)

Caveats and warnings

This is my first experiment with MicroPython and the Thumby, so it's probably an inefficient mess in the eyes of a "real" MicroPython developer. But this is a fun learning project for me 😄

There are a couple of small known issues, see below if you run into trouble.

Installation

Silicon8 is in the Thumby "Arcade". You can install it with a couple of clicks by going to arcade.thumby.us.

However, the arcade sometimes glitches out, in which case you follow the steps below to install Silicon8 manually on your device.

Get the MicroPython files from this Github repository if you know your way around git or download the ZIP file for the latest version on the releases page. Put the *.py files in /Games/Silicon8 on your Thumby using the Thumby Code Editor:

Connect your Thumby, wait for the file system tree to load
Right-click on "Games" in the file system tree and select "New folder"
Type in Silicon8 and press Enter
Click "Upload" at the bottom of the file system panel, select all the .py files from /Games/Silicon8 in this repository
Select /Games/Silicon8 as the destination path ("Final Path") on the Thumby and click "Ok"
Continue below to add some actual games

Getting CHIP-8 ROMs into Silicon8 for Thumby

CHIP-8 ROMs should be placed on your Tumby in the /Games/Silicon8/chip8 directory. To get you started, you can copy the games in this repository to your device:

Right-click on "Silicon8" in the file system tree and select "New folder"
Type in chip8 and press Enter
Click "Upload" at the bottom of the file system panel, select all the .ch8 and .ch8.json files from the /Games/Silicon8/chip8 folder in this repository
Select /Games/Silicon8/chip8 as the destination path ("Final Path") on the Thumby and click "Ok"
Disconnect and reboot your Thumby, you should now see "Silicon8" in the menu. Starting it should show you all the game ROMs you copied.
Select a ROM file and start playing!

You can quit a running CHIP-8 ROM and return to the Silicon8 menu at any time by holding down the key combination LEFT, A and B.

Adding more CHIP-8 ROMs

You can put any *.ch8 file in your CHIP-8 ROMs directory and it will be picked up by Silicon8. You can find many ROMs on the Internet and in particular on the CHIP-8 Archive. If you want to, or if you need to change the controls or interpreter type, you can add a JSON file with the same name but an added extension .json (so somegame.ch8 would become somegame.ch8.json) to configure your ROM.

The JSON config file accepts this structure:

{
  "name": "The Classic Game of Pong",
  "link": "https://a-link-to.some/info/if-available",
  "desc": "A short and clear description of the game and its controls",
  "type": "SCHIP",
  "keys": {
    "up": 1,
    "down": 4
  }
}

All fields are optional. Valid options for type are AUTO (default), VIP, SCHIP or XOCHIP. Valid options for the keys are up, down, left, right, a and b for all the buttons on the Thumby. The numeric values are the corresponding keys to be pressed on the CHIP-8 keypad (0 - 15).

Known issues

The interpretation of CHIP-8, SCHIP and XO-CHIP should be pretty close to the originals. However, there are a few issues to be aware of. If you find issues that are not described below, please file an issue.

Display limitations

Due to the small screen size and the limited colours of the Thumby, Silicon8 for Thumby is currently limited to lowres mode (64x32 pixels) in monochrome. If your ROM uses hires mode, the central 72x40 pixels will be shown and the rest discarded, which doesn't make for great gameplay. When using XO-CHIP's four colour mode, only plane 1 will be rendered to the screen.

I have some ideas on how to improve this in the future, but I will need to play with the physical hardware some more to see if those ideas are feasible.

Sound limitations

The Thumby has a very simple speaker. Silicon8 uses it for the CHIP-8 beeper sound. The full XO-CHIP audio capabilities are not (yet) supported though.

The current Thumby library does not expose the speaker in a more complicated way than setting a frequency and a duty cycle. You can, however, bypass the library and talk to the pin directly. Implementing XO-CHIP audio on this low a level will be a bit of a chore, that I have not yet felt like doing 😄🎶

Speed

This interpreter is not particularly fast in the Thumby emulator. It's a lot faster, and quite playable, on the actual hardware though. If you have any ideas or suggestions on how to boost the speed, please let me know. An issue or pull request on this repository will get my attention.

Type "AUTO"

Like the original Silicon8, Silicon8 for Thumby has a mode "AUTO" that tries to auto-detect the right interpreter type. This doesn't always correctly identify SCHIP and XO-CHIP programs when they do rely on quirks for those platforms, but don't use any of the features of those platforms. You can easily work around this issue by specifying the interpreter type explicitly in the JSON config file that corresponds to your wrongly detected ROM.