Yet Another (Super) Chip 8 Emulator

Table of Contents

1. What is it?
2. License
3. Compiling
4. Running
   1. Requirements
   2. Starting the Emulator
   3. Running a ROM
   4. Screen Scale
   5. Execution Delay
   6. Memory Size
   7. Colors
5. Customization
   1. Keys
   2. Debug Keys
6. ROM Compatibility
7. Third Party Licenses and Attributions
   1. JCommander
   2. Apache Commons IO

What is it?

This project is a Chip 8 emulator written in Java. There are two other versions of the emulator written in different languages:

• Chip8Python
• Chip8C

The original goal of these projects was to learn how to code a simple emulator.

In addition to supporting Chip 8 ROMs, the emulator also supports the Super Chip 8 instruction set. Note that no additional configuration is needed to run a Super Chip 8 ROM - simply run the ROM the same way you would run a normal Chip 8 ROM.

License

This project makes use of an MIT license. Please see the file called LICENSE for more information. Note that this project may make use of other software that has separate license terms. See the section called Third Party Licenses and Attributions below for more information on those software components.

Compiling

To compile the project, you will need a Java Development Kit (JDK) version 8 or greater installed. Recently, Oracle has changed their license agreement to make personal and developmental use of their JDK free. However, some other use cases may require a paid subscription. Oracle's version of the JDK can be downloaded here. Alternatively, if you prefer to use a JRE with an open-source license (GPL v2 with Classpath Exception), you may visit https://adoptopenjdk.net and install the latest Java Development Kit (JDK) for your system. Again, JDK version 8 or better will work correctly.

To build the project, switch to the root of the source directory, and type:

./gradlew build

On Windows, switch to the root of the source directory, and type:

gradlew.bat build

The compiled JAR file will be placed in the build/libs directory, as a file called emulator-1.0.1-all.jar.

Running

Requirements

You will need a copy of the Java Runtime Environment (JRE) version 8 or greater installed in order to run the compiled JAR file. For most systems, you can install Java 8 JRE by visiting http://java.com and installing the Oracle Java Runtime Environment for your platform. This version of the JRE is free for personal use but contains a custom binary license from Oracle. Alternatively, if you prefer to use a JRE with an open-source license (GPL v2 with Classpath Exception), you may visit https://adoptopenjdk.net and install the latest Java Development Kit (JDK) for your system, which will include an appropriate JRE.

Starting the Emulator

By default, the emulator can start up without a ROM loaded. Simply double click the JAR file, or run it with the following command line:

java -jar emulator-1.0.1-all.jar

Running a ROM

The command-line interface currently requires a single argument, which is the full path to a Chip 8 ROM:

java -jar emulator-1.0.1-all.jar /path/to/rom/filename

This will start the emulator with the specified ROM.

Screen Scale

The --scale switch will scale the size of the window (the original size at 1x scale is 64 x 32):

java -jar emulator-1.0.1-all.jar /path/to/rom/filename --scale 10

The command above will scale the window so that it is 10 times the normal size.

Execution Delay

You may also wish to experiment with the --delay switch, which instructs the emulator to add a delay to every operation that is executed. For example,

java -jar emulator-1.0.1-all.jar /path/to/rom/filename --delay 10

The command above will add a 10 ms delay to every opcode that is executed. This is useful for very fast computers (note that it is difficult to find information regarding opcode execution times, as such, I have not attempted any fancy timing mechanisms to ensure that instructions are executed in a set amount of time).

Memory Size

The original specification of the Chip8 language defined a 4K memory size for the interpreter. The addition of the XO Chip extensions require a 64K memory size for the interpreter. By default, the interpreter will start w ith a 64K memory size, but this behavior can be controlled with the --mem_size_4k flag, which will start the emulator with 4K.

Colors

The original Chip8 language specification called for pixels to be turned on or off. It did not specify what color the pixel states had to be. The emulator lets the user specify what colors they want to use when the emulator is running. Color values are specified by using HTML hex values such as AABBCC without the leading #. There are currently 4 color values that can be set:

• --color_0 specifies the background color. This defaults to 000000.
• --color_1 specifies bitplane 1 color. This defaults to FF33CC.
• --color_2 specifies bitplane 2 color. This defaults to 33CCFF.
• --color_3 specifies bitplane 1 and 2 overlap color. This defaults to FFFFFF.

For Chip8 and SuperChip 8 programs, only the background color color_0 (for pixels turned off) and the bitplane 1 color color_1 (for pixels turned on) are used. Only XO Chip programs will use color_2 and color_3 when the additional bitplanes are potentially used.

Customization

The file components/Keyboard.java contains several variables that can be changed to customize the operation of the emulator. The Chip 8 has 16 keys:

Keys

The original Chip 8 had a keypad with the numbered keys 0 - 9 and A - F (16 keys in total). The original key configuration was as follows:

1	2	3	C
4	5	6	D
7	8	9	E
A	0	B	F

The Chip8Java emulator maps them to the following keyboard keys by default:

1	2	3	4
Q	W	E	R
A	S	D	F
Z	X	C	V

Debug Keys

Pressing a debug key at any time will cause the emulator to enter into a different mode of operation. The debug keys are:

Keyboard Key	Effect
ESC	Quits the emulator

ROM Compatibility

Here are the list of public domain ROMs and their current status with the emulator, along with links to public domain repositories where applicable.

Chip 8 ROMs

ROM Name	Working	Flags
down8	✔️

Third Party Licenses and Attributions

JCommander

This links to the JCommander library, which is licensed under the Apache License, Version 2.0. The license can be downloaded from http://www.apache.org/licenses/LICENSE-2.0.html. The source code for this software is available from https://github.com/cbeust/jcommander

Apache Commons IO

This links to the Apache Commons IO, which is licensed under the Apache License, Version 2.0. The license can be downloaded from http://www.apache.org/licenses/LICENSE-2.0.html. The source code for this software is available from http://commons.apache.org/io