Tech Report: CrossFire DUAL SLAVE !

[Jawed]

http://www.techreport.com/onearticle.x/8390

Curiously, the first thing DFI showed us was what they described as a pair of slave cards running together cooperatively. The DVI output to the LCD display was only hooked to one of the two video cards, and the system was running 3DMark05. I asked how the cards were sharing data, and the gent pointed to the north bridge chip between the two cards.

Blimey. I presume this is running AFR.

Makes me wonder how much data is actually going through the dongle.

Jawed

 

[Geeforcer]

So, what exactly does the image composition engine do?

 

[digitalwanderer]

So, what exactly does the image composition engine do?

Composes the image.

 

[Jawed]

What's funny is that Firing Squad didn't notice that they were witnessing a dual-slave configuration:

http://www.firingsquad.com/features/computex_2005_day_one/page3.asp



Jawed

 

[Geeforcer]

So, what exactly does the image composition engine do?

Composes the image.

Or not... Since two slave cards seem to get along without one.

 

[digitalwanderer]

Or not... Since two slave cards seem to get along without one.

Unless they communicate along the PCIe and the composite engine renders the final image still.

 

[Dave Baumann]

I've come to the conclusion that the compositing engine is a performance optimisation. As I mentioned in our article, Super AA mode transfers the images via PCI Express, and some followup on that indicates that, right now (it is likely to change in the future, they just haven't had time yet) the composite engine is is more or less bypassed altogether for Super AA.

However, what this tells me is that the chips themselves are capable of the compositing (well, for Super AA they can certainly blend - I have seen two standard boards running before as well), but it would appear that to achieve this current boards need to get the input from the PCI Express bus (there is also the question of whether there is native hardware for this, or its actually running some kind of shader program), but this is not the optimal in terms of performance. The composite engine remove any reliance on the bus for the "performance" modes, also removes any necessity if the graphics core compositing has some overhead, and makes parallelisation a little easier.

We'll see how this changes once they have a seies of boards that were built with this in mind from the off.

 

[suryad]

Err...so the 3dmark scores are alike then? IIRC the SLI top of the line 6800 ultra setups get a similar score as well. The ATI's seems more flexible and yet it seems like it is more in beta as of yet. Nice job...come on now I want to see 4 top end R520s in the Crossfire config!!

 

[Blazkowicz]

they can only see each other frame with their dual slave AFR setup, that's useful only for 3dmark

BTW I think there was almost no communication between the chips in the ATI rage fury Maxx, right?

 

[Geeforcer]

If this works properly, it could provide an interesting option for X800/850 owners setting up Xfire: either getting a master card OR buying a second, identical card in SLI-like fashion.

Going back to the question Jawed originally asked, what exactly does the dongle do?

 

[digitalwanderer]

Going back to the question Jawed originally asked, what exactly does the dongle do?

From what Dave just posted I'd guess that the dongle is what relays the info from the slave to the master cards composition engine and it can NOT communicate to the comp engine via the PCIe.

Right?

 

[Brent]

Going back to the question Jawed originally asked, what exactly does the dongle do?

http://www.hardocp.com/article.html?art=Nzc4LDI=

Texture and geometry data will be passed to each card over the PCI-Express bus. The high speed cable transmits raw pixel data which is fed to the compositing engine for final display out.

Perhaps with two slave cards one does the final composition? Perhaps the one in the primary PCIe slot?

 

[hoom]

Ya know, there is a front page to B3d...
http://www.beyond3d.com/reviews/ati/mvp/

 

[digitalwanderer]

http://www.hardocp.com/article.html?art=Nzc4LDI=

Great article Brent, a very educating and fun read.

 

[Geeforcer]

Going back to the question Jawed originally asked, what exactly does the dongle do?

http://www.hardocp.com/article.html?art=Nzc4LDI=

Texture and geometry data will be passed to each card over the PCI-Express bus. The high speed cable transmits raw pixel data which is fed to the compositing engine for final display out.

How does that reconcile with this:

http://www.xbitlabs.com/articles/video/display/crossfire_3.html

In order to set the CrossFire work, users will need one RADEON X800 or X850 card and a RADEON X800 or X850 CrossFire Edition graphics card equipped with Compositing Engine. DVI-I output of a typical graphics card should be connected to DMS port of CrossFire Edition card using a special cable provided with CrossFire Edition graphics cards. The CrossFire reportedly does not transfer data between graphics cards using PCI Express bus, even though initially the company planned to use this ability.

 

[Blazkowicz]

simple, you send data to both cards at once.

 

[Geeforcer]

Yes, I see where I "read" wrong.

 

[Geo]

This might be a nice option for the 12-piper PRO folks.

Any word on the earliest CAT that supports Crossfire?

 

[Dave Baumann]

Going back to the question Jawed originally asked, what exactly does the dongle do?

Read my post above!

 

[Unknown Soldier]

The dude from DFI then swapped in a true CrossFire master card from ATI alongside one of the the X850 XT PE cards and proceeded to flash the slave card to what he said was a Radeon X800 BIOS, so it would match the CrossFire card. Both had dual-slot coolers that looked for all the world like X850 XT cards, but whatever. He then ran 3DMark for us again, this time with the video cables daisy chained as one would expect for a CrossFire config:

This master-slave configuration with slower cards produced a slightly lower score than the dual-slave X850 XTs, but it was still crazy fast. I noted, as 3DMark's Game 3 test ran, that there was some slight frame-to-frame jumpiness that seemed rather out of place, since everything else looked so very smooth and fast. Apparently, this setup still isn't working 100% as it should, but the performance promise is obvious.

http://www.techreport.com/onearticle.x/8390

Umm?? He had a X850XT Master card with a X800 Slave? Is that what is being said?

US