Exodus - A cycle-accurate Mega Drive/Genesis Emulator

http://www.assemblergames.com/forums/showthread.php?45726-Cycle-accurate-Mega-Drive-emulation-Exodus-coming-in-April!

by bane • 13 years ago

40 20 13 years ago

frozenport• 13 years ago

How is Exodus different than MAME?

techtalsky• 13 years ago

MAME is a project to emulate Arcade games. This is a project to emulate Sega Genesis/Megadrive games. Although many already exist, they use a lot of different tricks to help performance. Some of these hacks can cause game-breaking timing problems in some games. A cycle-accurate emulator takes a lot more processing power, but allows for the most accurate emulation of the games.

bane4• 13 years ago

Different goals it sounds like. MAME is intended to try and archive and emulate every arcade game known, the emulation doesn't have to be 100% so long as the experience of game is more or less playable. MAME likely contains code that replicates hundreds or even thousands of discrete architectures, probably sharing some common emulation cores, but lots and lots of custom code.

Exeodus appears to be more like a framework for describing different system architectures and enabling cycle accurate emulation (see BSNES/Higan [1]). As a test case, the author focused on the Mega Drive/Genesis...but it sounds like if you have a descriptor file of an architecture and the necessary components available, you could cycle-accurate pretty much anything, even systems that never existed!

I can imagine a community of authors that put together a library of different system descriptions that you load before loading a ROM or a disk image.

1 - http://byuu.org/higan/

Exodus is intended as a general purpose, cyc

Scaevolus3• 13 years ago

MAME prefers 100% accuracy over playability, and does cycle-accurate emulation.

The amount of custom code in each architecture is minimal-- it's mostly setting up memory maps and connecting the various chip emulations together.

bane4• 13 years ago

"This emulator is fundamentally different to every other emulator I know of, in several critical ways. I'll publish more about that towards the time of release, but most importantly, Exodus is not a Mega Drive emulator. Exodus is a generic emulation platform, which allows systems to be assembled from individual components at runtime. Nothing related to a particular system is hardcoded. Exodus constructs a system from a set of discrete components, manages the communication between those components, and keeps perfect timing accuracy between each component. Other systems can easily be modelled without modifying or rebuilding Exodus, it simply requires emulation cores for each device in that system to be available."

Woah...this could be extremely cool.

Scaevolus3• 13 years ago

MAME has been doing basically this for 15 years-- arcade cabinets are simulated by combining various common chips (CPUs, video drivers, sound chipsets, ROMs...) with a small amount of glue code.

Moving the glue code from a .c file to runtime makes it faster to tweak, but it's not a new idea.

Brashman• 13 years ago

The gem5 simulator (http://www.gem5.org/Main_Page) sounds like it works in a similar way to let you hook together different components and simulate different systems. Although gem5 is a research tool and not targeted to specifically emulate real devices.

pasquinelli• 13 years ago

"Exodus is also an extremely powerful debugging, development, and analysis environment, which I'm hoping will be able to serve as a very useful tool for communities involved in development, hacking, and reverse engineering, to be able to do more complex and thorough debugging and testing in software, where you can trust that if it runs properly in Exodus, it will run the same way on the real hardware, and vice versa."

this sounds cool. i'm not huge into the emu scene, but i haven't come across any emulator that has a debugger.

clobber• 13 years ago

> but i haven't come across any emulator that has a debugger

Mednafen, Stella, FCEUX just to name a few

jbit• 13 years ago

Indeed it's rare, but not unheard of. For example the "nocash" series of emulators has extensive debug support (breakpoints, memory viewers, disassemblers, hardware traps, etc)

http://nocash.emubase.de is the website if you want to check them out.

aidenn03• 13 years ago

""Most of the time, a timing problem is not going to occur. Given that assumption, I want to execute my devices unsynchronized for as long as possible. If something ends up happening in the wrong order, I want to roll back to the previous point, and repeat the operation, this time with fore-knowledge about the timing requirements". This is the execution model Exodus uses. By executing in parallel for as long as possible, we can make use of multiple cores. "

This is bad for an emulator; you want to minimize latency and jitter over throughput. It doesn't matter too much if your game is fast enough for 98% of the frames if the other 2% of the frames stutter.

Scaevolus3• 13 years ago

As long as each frame ends up being ready on time, having variable latency and jitter for segments of code is not a bad thing-- users can't tell.

aidenn03• 13 years ago

I am highly skeptical that consistent frame rates will be possible with this architecture; IIRC byuu considered and rejected such an architecture for bsnes for performance reasons. Granted hardware has advanced since then, but single-threaded performance hasn't advanced a whole lot in that time, and that's what you're going to run into a bottleneck with this.

lubujackson• 13 years ago

Sounds beautiful, can't wait to see it!

Exodus - A cycle-accurate Mega Drive/Genesis Emulator

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