Vs. DualSystem support

Do any emulators support Vs. DualSystem games? I imagine this would have to tie into netplay if supported.

As far as I know, only MAME.

The wiki does not go into a lot of detail about the Vs. DualSystem. What makes it difficult to emulate?

Nothing much? It's just two 2A03s and two RGB PPUs all running off the same clock. The shared memory and IRQ handshaking is the only weird thing, and that's probably only hard with emulators that use catch-up optimizations.

If I had to guess why it's so rarely emulated? There's only six Dualsystem-requiring games according to Nocash and Wrecking Crew is probably the only one that's compelling to western audiences...

In fact, since the two PPUs are running off the same clock, and /RESET for everything is tied together, and it's the RGB PPU, there's no missing pixel, so the two PPUs should stay genlocked forever, too.

Why does it use 2 CPUs and 2 PPUs? Does it show the games from 2 different perspectives (e.g. camera centered around player 1 on one screen and around player 2 on the other)?

Two screens is what makes it a dual system? Two screens requires two PPUs. And two sets of controls.

DualSystem cabinets had two CRTs, and it would have been stupid to make the arcade manager not use one whole set when they wanted to rotate out games... so two CPUs running entirely separate code.

Vs. Balloon Fight does have one player on each screen. Vs. Wrecking Crew seems to have a 2v2 setup, one team on each screen.

Speaking of this, it would be nice to get the frame timing confirmed for the RGB PPU. Likewise, would be nice to be able to fill in the missing information at http://wiki.nesdev.com/w/index.php/Clock_rate

Do we have anybody in here with a system with a 2C03/2C04/2C05 PPU that can run custom test ROMs?

(If the timings have been confirmed before: source?)

How are 2 CPUs wired up to the same memory?

What's unclear about the wiki?