Crossfire limitation

S

Slappi

Newcomer
I am not as tech savy as most of you here so does this sound like it is for real?

Max Crossfire resolution od 1600x1200@60Hz??

http://www.rage3d.com/index.php?cat=75#newsid33828812

Serious CrossFire Limitation
Today at 10:30 PM by Ratchet8 Comments
Earlier today I was given information regarding ATI’s upcoming Crossfire technology that, at first, I passed off as so ridiculous it couldn’t possibly be true. However, after having the information verified from several very reputable sources I’ve decided it would be a disservice to keep this information private.

As many are aware by now, ATI’s Crossfire technology uses an external link to connect the Master and Slave cards together (it's sort of like a 3-headed dongle with DVI connectors at the ends). What’s not generally known is that the backbone for this setup is a Silicon Image SiL 1161 chip which is installed on the X8-series Master cards. The SiL 1161 is there to receive output passed over the external link from the Slave card in the Crossfire setup and pass it on to the Master card.

Sounds decent on paper and everything, but if you check out the specs for the 1161 on this page you will see that it is limited to single-link TMDS @ 165MHz. This means that the max 3D resolution for any X8-series Crossfire setup is 1600x1200 @ 60Hz! That means no high-res Crossfire gaming beyond 1600x1200, no 1600x1200 at a flicker free refresh rate, and no widescreen 1920x1200!

How can a technology so clearly aimed at enthusiast gamers have a limitation like this? High-resolution flicker free gaming is one of the primary benefits a multi-graphics setup like Crossfire should offer entusiasts but, somehow, ATI managed to mess that up completely.
 
I was first told about this Sil 1161 chip 2 weeks ago. And I have been poking my nose around specifications myself. I also asked a few reviewers if was stll there. The limitation is true. At least from my understanding of it is that limitation is still there from what I have been told about the chips presence. But personally I felt it was worth waiting till a finished product before mentioning it. I figured its possible it could be changed from now till then.
 
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Oh, good grief. If that's true, scratch this generation of CrossFire as a serious competitor. And Maybe the R520 generation too if they didn't upgrade there. Ratchet isn't the nervous-nelly sort, but I sure hope he's wrong about this.
 
If that should be true than the 60Hz limitation affects mostly the few remaining CRT users out there. We are a dying breed ;)
 
Ailuros said:
If that should be true than the 60Hz limitation affects mostly the few remaining CRT users out there. We are a dying breed ;)
Click to expand...

I suppose the "Super AA" crowd with LCDs is still in play, but still, this would be a major blow at their ability to attract the tippity-top crowd that makes up a very large percentage of SLI users, as I understand it.
 
Interesting, I dont see how something that big could get past testing and on to a final product. What the hell would be the point of even going Crosffire with this limitation, all the high end cards have no problem doing 16x12 on anything right now.

But here's a question: Is it a bandwidth issue? How easy can this be fixed? How the hell did ATi let this pass? Sigh.
 
Skrying said:
Interesting, I dont see how something that big could get past testing and on to a final product. What the hell would be the point of even going Crosffire with this limitation, all the high end cards have no problem doing 16x12 on anything right now.

But here's a question: Is it a bandwidth issue? How easy can this be fixed? How the hell did ATi let this pass? Sigh.
Click to expand...

You presume an "oops". I don't see how it can be (if it exists at all).
 
Does that assume the cards are sending the full frame across the link or only the 50% that the card is actually working on? If its only sends 50% you'll get 1200x1600 at 120 Hz
 
I read Ratchet's post, and what I get out of his source checking is that this has been confirmed, even if he can't tell us who --but if he could, we'd accept it too.

Love to be wrong. Love to think that one of the reasons it is late is they were figuring a way around this issue. But I'm having a hard time convincing myself that might be it.
 
We do, of course, realise that Crossfire uses the DVI output of existing cards for the slave image, yes? Has anyone considered the limitations of what that is?
 
geo said:
I suppose the "Super AA" crowd with LCDs is still in play, but still, this would be a major blow at their ability to attract the tippity-top crowd that makes up a very large percentage of SLI users, as I understand it.
Click to expand...

It's too late for my budget that consider anything apart SLi for the future, since I'm "merely" lacking one GPU to complete it. I have a 21" CRT that can reach 2048*1536*32@75Hz, but as I explained before I don't gain that much beyond 1600*1200, since with anything beyond a 1200 height the monitor is stretching content (think of some sort of "oversampling"). It doesn't look bad at all, just not necessarily that much better than "real" 1600*1200.

An LCD user with a 1600 native resolution won't have a problem on a CF system if the above is true; the only other alternative would be the large LCD monitors from Apple for instance, which I'm personally not very fond of as an idea either since then the user is bound to an ultra high native resolution. Anything lower than that will look like crap and the more pressing question then is that how long exactly you'd be able to sustain an acceptable performance level in >19xx-whatever resolutions even on a dual-GPU system.
 
Heh, I guess it takes 3 months for info to filter down to Rage3d...:)

My old post is here. Yep, it's half frame transmitted, but after final compostion the output is still 60Hz limited by the output of SiI1162.

Edit: Apparently the slave image transmits a "full frame", WETM.
 
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From the looks of it. SLI tends to support 2048x1536 analog output. I know my dual Geforce 7800 GTX cards can do it at 75 hz. And systems with dual link output seems to have a limitation of 2560x1600 @ 60 Hz. Just for reference sake.
 
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So, we have a limitation that was known about in June (hell, I'm on that thread :smile: ), and now it is suddenly getting big play right before release? There wouldn't happen to be a poison pen. . err, "competitive analysis" email floating around now, would there? With suitable "but don't mention it came from us" instructions? Maybe some catchy wording in the slammies here and there?

Gad this business is slimy some times. Worse than the CIA in use of surrogates, cut-outs, and plausible deniability when there's "wet work" to be done. . . If you're gonna do it, take responsibility for it.
 
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Yeah, now that I think more about it, I really think that the problem is as bad as it sounds. Consider:
1. Crossfire is designed as a solution where one of the boards has no knowledge that it is working in tandem with another.
2. The compositing engine is separate from the core logic of the master board.

So, we can expect that Crossfire uses the normal output of rendering part of a frame in order to produce output. Thus, when using split-frame rendering or supertiling, it seems that there will indeed be a limit set at 1600x1200@60Hz.

I'm not really sure how alternate frame rendering fits into all this, however. Perhaps ATI's hardware can be told to run at lower refresh rates than 60Hz (say, 30Hz or 42.5Hz) for the recompositing, to enable up to 1600x1200@120Hz. But one would think that this could severely impact framerate if triple buffering is not used.

For ATI's sake, one would hope that this will be fixed by the time that Crossfire is actually released, but that still means that anybody with current ATI hardware can't realistically upgrade to a Crossfire solution and expect to run at the highest resolutions, from what I can see.
 
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