jemu

Multi-system emulator written in Java.

Supported systems

System	CLI identifier	Status
CHIP-8	chip8	✅ Supported
STRICT CHIP-8	strict-chip8	✅ Supported
CHIP-8X	chip8x	✅ Supported
CHIP-48	chip48	✅ Supported
SUPER-CHIP 1.0	schip10	✅ Supported
SUPER-CHIP 1.1	schip11	✅ Supported
SUPER-CHIP MODERN	schip-modern	✅ Supported
XO-CHIP	xochip	✅ Supported
MEGA-CHIP	megachip	✅ Supported
HyperWaveCHIP-64	hyperwave-chip64	✅ Supported
VIP CHIP-8	vip-chip8	✅ Supported
VIP CHIP-8X	vip-chip8x	✅ Supported
COSMAC VIP	cosmac-vip	✅ Supported
RCA Studio II	rca-studioii	✅ Supported
Game Boy (DMG)	gameboy	✅ Supported
Game Boy Color (CGB)	gameboy-color	✅ Supported
Nintendo Entertainment System	nes	✅ Supported
Atari 2600	atari-2600	✅ Supported
Commodore 64	c64	✅ Supported
Apple II	—	🗓 Planned
Space Invaders arcade cabinet	—	🗓 Planned
Sega Master System	—	🗓 Planned
ZX Spectrum	—	🗓 Planned
Sega Genesis	—	🗓 Planned
Super Nintendo Entertainment System	—	🗓 Planned

Keybindings

CHIP-8 / STRICT CHIP-8 / CHIP-8X / CHIP-48 / SUPER-CHIP 1.0 / SUPER-CHIP 1.1 / SUPER-CHIP MODERN / XO-CHIP / MEGA-CHIP / HyperWaveCHIP-64 / COSMAC VIP / VIP CHIP-8 / VIP CHIP-8X

Keypad key	Keyboard key
1 2 3 C	1 2 3 4
4 5 6 D	Q W E R
7 8 9 E	A S D F
A 0 B F	Z X C V

RCA Studio II

Keypad A	Keyboard key
1 2 3	1 2 3
4 5 6	Q W E
7 8 9	A S D
- 0 -	- X -

Keypad B	Numpad key	Keyboard key
1 2 3	7 8 9	7 8 9
4 5 6	4 5 6	U I O
7 8 9	1 2 3	J K L
- 0 -	- 0 -	- , -

Game Boy / Game Boy Color / Nintendo Entertainment System

Action	Key
D-Pad Up	W
D-Pad Down	S
D-Pad Left	A
D-Pad Right	D
A	J
B	K
Start	Enter
Select	Backspace

Atari 2600

Action	Key
Game Select	E
Game Reset	R
Left Joystick Up	W
Left Joystick Down	S
Left Joystick Left	A
Left Joystick Right	D
Left Joystick Fire	F
Right Joystick Up	I
Right Joystick Down	K
Right Joystick Left	J
Right Joystick Right	L
Right Joystick Fire	;

Commodore 64

The Commodore 64 core uses symbolic keybindings for the built-in keyboard.

Action	Key
A-Z	A-Z
0-9	0-9
Left Arrow	`
£	~ (Shift+`)
!	! (Shift+1)
@	@ (Shift+2)
#	# (Shift+3)
$	$ (Shift+4)
%	% (Shift+5)
Up Arrow	^ (Shift+6)
&	& (Shift+7)
*	* (Shift+8)
(	( (Shift+9)
)	) (Shift+0)
-	-
=	=
+	+ (Shift+=)
Commodore	TAB
CLR/HOME	\
Shift Lock	Caps Lock
:	: (Shift+;)
[ (Shift+:)	[
;	;
] (Shift+;)	]
Return	Enter
`	'
" (Shift+2)	" (Shift+')
Left Shift	Left Shift
Right Shift	Right Shift
,	,
< (Shift+,)	< (Shift+,)
.	.
> (Shift+.)	> (Shift+.)
/	/
? (Shift+/)	? (Shift+/)
Ctrl	Ctrl
F1	F1
F2 (Shift+F1)	F2
F3	F3
F4 (Shift+F3)	F4
F5	F5
F6 (Shift+F5)	F6
F7	F7
F8 (Shift+F7)	F8
RUN/STOP	ESC
RESTORE	F12
Up (Shift+CRSR UP/DOWN)	Up
Down (CRSR UP/DOWN)	Down
Left (Shift+CRSR LEFT/RIGHT)	Left
Right (CRSR LEFT/RIGHT)	Right
Space	Space

Peripherals:

Action	Key
Joystick 1 Up	Numpad 8
Joystick 1 Down	Numpad 5
Joystick 1 Left	Numpad 4
Joystick 1 Right	Numpad 6
Joystick 1 Fire	Numpad 0

Datasette:

Action	Key
Play	Home
Stop	End

Command-line usage

If you launch jemu from the CLI, you can optionally pass arguments.

Usage:

jemu [-hV] -r=<romPath> [-s=<system>]

Argument	Description	Default
-r, --rom <path>	Path to the ROM file.	—
-s, --system <identifier>	Launch with the specified system selected, or omit to use the saved setting or system detected from ROM file extension, if specified. See supported systems for valid identifiers.	—
-h, --help	Show the help message and exit.	—
-V, --version	Print version information and exit.	—

On startup jemu will attempt to perform a power-cycle with the provided, detected, or saved system and specified ROM file, if any.

Dev Builds

The repository has a Github Actions workflow that runs on every push to the dev branch and contains native app image artifacts for Windows, MacOS and Linux, which will stay available for 90 days afterwards: https://github.com/ArkoSammy12/jemu/actions/workflows/dev-build.yml

These builds are not well tested and may have bugs.

Building

A Java Development Kit targeting Java 25 or later is required to build this project.

This repository contains git submodules. When cloning, use the --recurse-submodules flag to ensure they are all downloaded correctly.

Once cloned, run the following from the top-level directory:

Windows:

.\mvnw clean package

macOS/Linux:

./mvnw clean package

An executable .jar file will be generated at target/jemu-x.y.z.jar.

To skip the automated unit tests, append -DskipTests to the build command.

License

This project is licensed under the MIT License.

Special thanks

• Steffen "gulrak" Schümann: Significant help during my CHIP-8 emulation journey, serving as my primary guide and advisor. He has also generously lent me his STRICT-CHIP-8 implementation. Also of great help during the development and debugging of my Commodore 64 core.
• Mathew "theklap" Sutton: Significant accuracy improvements to the NES core.
• dtabacaru: Providing audio filtering logic to system's audio processing units.
• Shawn (L. Spiro) Wilcoxen: Provide accurate audio filtering classes useful for quality NES APU output, and the amazing Ricoh 2A03 instruction reference.
• Andrew "ajoneil" O'Neil: Significant accuracy improvements to the DMG/CGB cores.
• The Stella Team: Implementation of the Atari 2600's audio LFSR mechanism.
• sidera: Aided in the implementation of the Commodore 64 SID.