[nathanb]

Do you think this is because of difficulty in emulation or because the X-Box was so easy to hack? It was not super expensive to buy a used X-Box and mod it even back when new games were coming out for it, so maybe it just didn't seem like a worthwhile investment to spend time writing an emulator?

[Springtime]

I'd recommend reading this post [1] by the dev of an existing Xbox emulator. It's a summary of the issues inherent to the emulation of the original Xbox, highlighting some major hurdles and technical difficulties that would have to be overcome.

[1] http://www.neogaf.com/forum/showpost.php?p=48088464&postcoun...

[daeken]

Having spent a lot of time doing Xbox emulation, the biggest issue is simple: statically linked XDKs meant that doing high-level emulation was next to impossible. You had to find signatures for every XDK, which isn't viable considering that most of them weren't publicly released.

LLE/MME can work, but it's significantly more effort to pull it off; that's the approach I was taking, when I was still working in it.

[MichaelGG]

"The real problem is that any modern x86 processor including the Pentium III can execute multiple instructions at once. So it's not like emulating a Z80 doing one instruction at a time. The actual algorithm and how x86 does this is undocumented and still unknown. In short, the Xbox's CPU can be emulated, but not accurately."

How is that relevant? Is there any code compiled for the Xbox that actually relies on how the P3 handles microops and pipelines things and all that? Cause if your argument is "X=A+B+C+D" might have several different ways of happening, the answer is that it doesn't matter. So I'm not sure why the author bring this up.

The Wii chip is also OOO but Dolphin seems to do a fantastic job.

[DCKing]

Perhaps they know the PowerPC's algorithm for performing out of order execution? It might have been available for a long time, or have been shared to the public after IBM started opening up the Power architecture since 2004.

[MichaelGG]

Or most probably: it doesn't matter at all since compilers aren't generating code that depends on such details?

[maaku]

CPUs (x86 or PPC) only do out-of-order execution when it is provably the case that it doesn't matter. The result of running any given sequence of instructions in lock-step, or out-of-order should be exactly the same. If not, you found a CPU bug!

That said, timing matters in these tight inner loops, and that is where the details of the CPU pipeline matter, with respect to emulators. How many nanoseconds would it have taken for the emulated CPU to execute those instructions? That requires knowledge of how the CPU works. And sometimes, unfortunately, game code stupidly depends on these details.

[MichaelGG]

With newer-gen high-level consoles and emulators, is that really the case? Having cycle/instruction accurate emulation only seems to be an issue for older consoles (PS2 and before?) where programmers actually relied on all sorts of things to eek out every cycle's worth.

On the Xbox, is that really the case?

[herokusaki]

Why doesn't the developer's post address the possibility of visualizing the CPU rather than emulating it?

[Narishma]

I don't think you can get accurate emulation that way. You may end up with games running at different speeds depending on what CPU you have. Some may be too fast or too slow to be playable.